Breathable Walls

Jay asked me to do a book review on George Swanson’s “Breathable Walls” that includes the envelope (walls, foundations, roof, floors). Out of respect for George I’m not going to reveal all that is in his book. I will however for the sake of the natural building community and in an attempt to correct the way some think share some key concepts for discussions. Although the book does challenge plastic barriers used in mainstream construction popular in some countries, I don’t want to turn this into a debate on it, rather stay focused on what is in the book. George has reached out to a large network of experienced educated professionals that are listed in the book he refers to as “Building Biologist” from all around the world including Germany and American “Building Scientist”.

Myself included have been misled by debatable r-values, permeability ratings, and ventilation rates, derived out of the manufacturing industries. When it comes to breathable walls there is a lot more that needs to be understood and it can get complex dynamically, those metrics do not accurately measure.

So I’ll start with some basic principles the book offers for discussions. If you are not sure ask question, or, have been trained by mainstream it would be best to ask questions rather than make comments that may be inaccurate or not applicable to breathable walls. I’ll look through the book and try and answer any questions. I am learning too. This area of a building from what I have gathered is highly controversial and misunderstood even by the “Pro Building Scientist” many of the more popular ones have contributed to this book and are noted throughout.

“Thermal Mass” is another term often used. Since it is dynamic r-value and perm ratings alone can be misleading. In my opinion “Breathable Mass” or “Hygrothermal Mass” would be more appropriate especially with regard to natural materials that exhibit these superior properties, whereas a lot of plastic based manufactured materials do not. Seems to me by not coming up with more accurate metrics and understanding keeps the confusion level up and the debates ongoing, employing the mainstream building scientist and “greenwashed” websites. Many of them, including American code, are just not interested in what George and other Natural or Building Biologist have to say and eliminating the confusion.

Studies have shown that buildings need to dry within 24-48 hours before mold develops, that is the window in general. “Hygrothermal Mass” needs to satisfy three conditions to accomplish this: 1. Permeability and diffusion. 2. Hygroscopic absorption & adsorption. 3. Capillary absorption & adsorption.

1. Vapor “permeability" is rate of movement of water molecules H20 through or within materials usually small from infiltration. “Infiltration” is between materials by air and higher movement. Permeability does not play a profound role in some building materials allowing moisture to escape before mold sets in. The physical process responsible for perm is called diffusion.

Attached are some perm rating of materials to compare.

Diffusion of moisture in air involves movement of water molecules as well as the molecules of oxygen, nitrogen, and minor components such as carbon dioxide. Net diffusion is driven by a gradient of airborne water vapor concentration or H2O partial pressure. Water molecules dissolved in the vapor phase are spontaneously transported from volumes of higher concentration to those of lower concentration affected by pressure and temperature.

I'll stop there since it only gets more complex for any questions and comments

Thanks Terry, that's a great resource and very interesting!

It also eases my conscience as I use a lot of drywall in my restoration work because of speed and ease of installation. I have always felt a little uneasy about it though because it is not a material available to the original builders and because I was unsure if it would change the vapor dynamics of a well functioning lime plastered wall assembly. Now I see that the drywall is more permeable than even the rock wool insulation that I use!

I am a home inspector/energy auditor and home restoration/renovation contractor, so I have seen what works and what doesn't first hand. Over and over I see the same mold/rot problems with the same materials, listed high on your list since they are not able to dry effectively. Many of the breathable older homes have had serious degradation to them due to being sprayed with a heavy coat of latex paint. These homes worked well, until some well meaning but undereducated contractor remuddles the place with concrete, plastic, rubber and fiberglass; then ruin is only a few decades away.

Bill, thanks for participating....I wish more did. We are just getting started. The book states that besides permeability and it's means of operation "diffusion" through a material, to make a material "hygrothermal" building scientist have found that the other two physical properties it needs to have to transport moisture are 2. "hygroscopic" absorption/adsorption and "capillary" absorption/adsorption. I think you will see the problem with drywall in the later two I will get to after we finish with permeability and diffusion.

More to chew on below... there is a little more I will write up tomorrow on perm and diffusion then we can look at the other two. You know, when I use to look at perm rating's on material data sheets and that is all that was being discussed I always said there is moisture content (MC), the surface behavior which is being referred to as "adsorption" that has to effect perm rating's. Capillary action I never made the tie to perm and MC. More interesting stuff to come, the book does an excellent job putting it all in perspective. Very technical, I am having to read it several times to get it to sink in since it changes the way I think.

I'm going to move through this fast so feel free to jump in and help figure this out...

-In a realistic building rendering of building moisture a mixing of pure gases occurs to an equilibrium in stages. Only about 2% of the molecules in water vapor saturated indoor air (100% RH @ 68F) are actually H2O. Depending on the temperature, outdoor air at @ 100% RH contains anywhere from 1 % H2O (@ 0 F) to about 5% H20 @ (95% F). Under realistic conditions at least 95% of the molecules are oxygen and nitrogen.

-The rate of diffusion is determined by pore structure and is significantly hindered at pore diameters of less than .05 microns, which is less than one hundred the diameter of a human hair. Still about 100 water molecules will fit in the diameter of a .05 diameter pore. Progressively slower diffusion occurs at orifices less than .002 microns.

-The movement of water should not be confused with the flow of air. The two are not even necessary in the same direction. Water movement is often from inside out due to showers, hot water heaters, respiration of occupants, etc….Air pressure, on the other hand, results from wind and temperature changes that vary throughout the building depending on wind direction and related factors. Mechanical ventilation, if used, can produce negative indoor pressure.

-As a practical matter, vapor permeability due to H2O diffusion through breathable walls plays only a very minor role in supplying fresh outdoor air to make a building comfortable and healthy. More on natural ventilation later.

I'm going to be building a small cabin this summer in northern new england. The cabin is around 350sqft on slab. heat will be with RMH. ventilation will be either exhaust only or passive with windows, or a combination of that.

My goal is for a fairly tight envelope that doesn't trap moisture inside the wall, significant passive solar gain, and high interior thermal mass.

My question is about a walls ability to dry to the interior. the assembly that I'm planning is below:

from interior to exterior:

-wood finish
-2x4 wall frame with dense pack cellulose
-zip system wall sheathing - taped
-4" rigid foam
-3/4" air space/rain screen/strapping
-wood siding, probably vertical board/board or board/batten

curious what peoples thoughts are about this choice.

Dale Walker wrote:

I'm going to be building a small cabin this summer in northern new england. The cabin is around 350sqft on slab. heat will be with RMH. ventilation will be either exhaust only or passive with windows, or a combination of that.

My goal is for a fairly tight envelope that doesn't trap moisture inside the wall, significant passive solar gain, and high interior thermal mass.

My question is about a walls ability to dry to the interior. the assembly that I'm planning is below:

from interior to exterior:

-wood finish
-2x4 wall frame with dense pack cellulose
-zip system wall sheathing - taped
-4" rigid foam
-3/4" air space/rain screen/strapping
-wood siding, probably vertical board/board or board/batten

curious what peoples thoughts are about this choice.

Dale, this is a typical popular mainstream wall assembly that is highly misunderstood since it has not passed the test of time. Alot of folks speculate on walls focusing on whether they will dry a certain direction, many are mislead. It's not only keeping a wall "dry" that is important, dry needs to be broken down as we are in this thread, it means a lot of things. The question that needs to be asked is "will my wall assembly produce fungi and rot?" or "does it have food, temperature, moisture to grow fungi/mold" and rot my structure, materials, health?

So instead of just looking at stacked up perm rating's, air seals, take a look at the chemical make-up of materials that you are putting together and ask yourself if they are compatible?

Hurber "ZIP" like all plastic/wood "engineered" boards has not been around long and the manufactures doe not provide enough data on compatibility with other materials, health risk, nor life cycle test on tapes, glues, resigns, etc, that in your harsh climate zone especially probably will not last. If you look outside of ZIP, at many adhesives there is plenty of data that points to a short life cycle, ZIP will be no different. Look for "fatigue testing" you will not find @ Hurber from thermal and pressure cycles of there ambient temp cured peel and stick tapes, factory cured boards.

Take a look at the MSDS and known toxins: http://www.huberwood.com/assets/user/library/ZIP_R-Sheathing_MSDS1.pdf

1. MDI resign
2. Formaldehyde
3. Blowing agents
4. Fire retardants

All food for mold. We definitely cannot say they are a natural fungicide or insecticide like lime, clay, MGO, etc. Take a look at your foam manufacture. All walls will see moisture in it's life it is proven so plan for it, some more than others. The second source of fungi growth besides food that, if the drying is slow less than 24-48 hours, and the temperature is right, depending on the spore.....ZIP has no data on drying speed. Your going to have to regulate your indoor humidity to keep it out of the wall drying inward 24/7, and make sure none gets in through the exterior. Good luck! You'll find a lot of people say without knowing what there wall humidity levels are say they will keep indoor @ 40-50%, guessing! ZIP and your foam choice, use their r-zip if you are going to go with this route.

Take a look at the stability of the products you stack, "materials to avoid, decomposition" in the MSDS....and if you do not understand do not design with them.

This wall assemble is not a natural "breathable wall" by any stretch of the imagination, if is full of toxins and moisture and heat traps so, I am not going to spend any more time on it. Lets stay focused on natural material choices that perform much better at self regulating mold growth and indoor humidity. Wood does not provide alot of "hygrothermal Mass" indoors or for solar passive or humidity control that lowers cooling loads. There are better choices, it also conducts heat, so you have to be careful it does not thermally bridge indoor air to outdoor and visa-versa...the answer for alot of folks is foam or Sips wraps, they ignore the toxic blowing agents and fire retardants and hope a dew point moves to foam when the material cannot manage moisture if it does, like clay renders for example.

Trust me Dale you don't want to know "peoples thoughts" that probably don't even look at the data or know. At a minimum you should provide perm rating's, moisture contents, chemicals, for people to even begin to know what they are talking about. There are plenty of wrong opinions out there on mainstream sites. Also, the MSDS only list what is hazardous to workers, they are not required to list life cycle hazards to homeowners, in America anyway.

Follow this thread and I think you will see for yourself what makes a breathable healthy wall.

Thanks Terry, I appreciate your insights. Coming from a world of modern "traditional" building, I don't have much experience with natural wall assemblies, though I am very intrigued to learn more. Would you feel comfortable suggesting any assemblies that you would use in my climate zone?

I'm looking forward to following this one

Dale, there is a lot to deciding what materials, means, and methods to use in a climate zone. You also have to consider the skill sets of the trade’s available, local materials, machinery, banks, real estate and insurance agents, building codes, cost, etc, depending on needs. As a builder I have a lot to consider. I’m am still looking for a way after years of research myself, now to not go too far away from the trades I have at hand, use some of mainstream construction labor we currently have but, with more natural materials for now. It will easier to get past all the red tape, then slowly more to other natural builds (rammed earth, hemp, clay-slip, etc). You have a lot of wood and natural builder in your state I do not. Magnesium board and cements have my interest the books looks at later. The best approach is to find ones that work for you based on a wide array of knowledge and local research or hire an architect or builder if you can find one that knows all this, rare. I’m probably heading to pay the author a visit soon since he has done all this. I wanted to read his book first to at least be able to communicate well with him when we do meet. Yestermoore in VT might be able to hook you up with a mentor.

Back to Breathable Walls…So to recap, according to studies noted in the book “only 2% of moisture “walks” through the breathable wall. Not much but enough to allow moisture that does enter find its way out. The main point here in applying the principles of permeability and diffusion is that breathable walls defy commonly accepted logic in modern building’s practices. This is because they allow moisture to move into and then out of a wall without causing mold growth or structural damage. At the same time they provide the one thing you would not expect from a porous, low density wall structure, excellent thermal performance. The latter is possible because unlike infiltration (between and through materials) diffusion is slow and therefore so is the rate of heat transfer especially in thick mass walls (lag time, also referred to as heat capacitance (more later) that dry moisture out. Also, aside from moisture, diffusion also plays a role in improving indoor air quality via the slow outgassing, dissemination and removal of volatile organic compounds (VOC). Nevertheless, it should be understood that VOC’s are often unable to pass through moisture-permeable materials and must be removed by ventilation. It is preferred that they be eliminated by not applying them in the first place.

Next, “Hygroscopic Adsorption/Absorption”. This is where it starts to get interesting….

2. Hygroscopic absorption/desorption

Most experts consider hygroscopicity to be the hallmark of breathability. The fundamental chemical property is adsorption (not to be confused with absorption) a physical mixing of materials. Adsorption has to do with behavior at the surface of a material, we focus on one of two, “chemisorption” as described in text by “adsorption” often very weak. Physisorption involves the formation of multiple layers of molecules on a solid surface due to even weaker physical forces, without chemical bonding. Hygroscopicity has to do with chemical bonding so the focus is on it.

In adsorption a gas molecule such as H20(an adsorbate) forms a chemical bond with a solid surface. The absorbate becomes an integral part of that solid, losing it’s own identity (no longer H20). Ideally this has to occur without “wetness” for mold growth no matter how much H20 is aDsorbed. A “hydrogen bond” is formed by the hydrogen in water and oxygen on the solid material that is the weakest of chemical bonds and readily reversible(the reversal or breaking of the chemical bond and release of water is called desorption)

The chemical nature of materials “surfaces” varies alot from one material to another. For H20 molecules to from hydrogen bonds, one needs suitable atomic structures on the surface to which they can bond. The most attractive structure for hydrogen bonding is what is known as the hydroxyl group (-OH), which is chemically very similar to H20. Surfaces such as unfired clay have many hydroxyl groups and are hydrophilic (water loving), whereas others, such as most plastics, have few -OH groups and are therefore hygrophobic (water repelling).

More food for thought. Next three conditions needed to satisfy hygroscopic materials….

Terry, great to look at this scientifically.

One thing not mentioned is that all of these processes are kinetically driven; meaning that they increase with temp and pressure. Basically, when temps are higher, more moisture will drive through a wall assembly than when cooler.

The thing that I get asked about most is condensation of water vapor as it travels through an assembly and the interstitial moisture left there. This is the reason for vapor barriers in cold climates. From my experience, this is effectively reduced by sintering the plasters used in order to reduce pore/grain size and reducing capillary adsorption/desorption. Once the surface of a natural plaster is saturated, then no more water vapor can be adsorbed. The plaster then diffuses from the saturated surface to the inner wall and as RH decreases, to the air. As you alluded to earlier, it is moisture content that is controlling the process and heat(kinetic energy) is driving it. So long as RH doesn't remain high for extended periods, vapor is not driven through the wall, but returned to the air.

So, back to my defending drywall as an acceptable building product when coated in a sintered mineral plaster. Often in my work, I am building insulated walls, covering them in drywall and connecting them to lath and plaster walls. Typically the lime plaster base coat is coated with a layer of gypsum and then lime washed/plastered. To match, I plaster the drywall with lime/gypsum and then finish with straight lime, no sand. The finish lime is heavily sintered/burnished to reduce capillarity and grain size which results in a polished look that reflects light well. Most people can't tell the difference between walls at this point.

I don't think we want much water vapor to walk through the walls, but we do want to hold it up and let it back into the home in order to maintain proper indoor RH.

Bill, yes the scientific reads are difficult for me to get my head around. I looked at the credentials of the three authors this morning. George has been all around the world building many natural homes, BS in Industrial Tech, and very experienced consultant today. Same with the other two, one of which is PHD in chemistry. Most of what I am sharing is not theirs persay, but they pulled in a lot of others with high credentials and test data. I’ll try and respond to your comments best I can based on what has been covered thus far but, do not take it as gospel I am still learning. It is good to have you that can relate the info into practical experiences.

I’ll refrain for now on how temperature alone affects vapor diffusion since “thermal mass” is upcoming and also Capillary adsorption/absorption which is noted as a grey area. Having read it changed the way I think or raised questions. In the labs I have worked in, we develop heat "flux" loads in a load cell based on inertia, yes an exchange of potential and kinetic energy is the physics part. There are several thermal and fluid dynamic formulas that apply here but it gets very complex. I, and I'll assume most, want a basic understanding. George warned me the beginning of the book was very technical to prove that natural breathable walls defy commonly accepted logic in modern building’s practices

Here is what I believe is stated about your comments,

“Diffusion of moisture in air involves movement of water molecules as well as the molecules of oxygen, nitrogen, minor CO2. Net diffusion is driven by a gradient of airborne water vapor concentration or H2O partial pressure. Water molecules dissolved in the vapor phase are spontaneously transported from volumes of higher concentration to those of lower concentration, until the concentration is uniform. This slow process is affected by both pressure and temperature. “ (There are some cartoon pics of this in the book to better illustrate the phase molecular stages).

So basically what I gather from that is the underlying processes is fluid dynamics based on concentrations, which is “affected” by thermodynamics. I took both courses 30 years ago in college and can not remember diddle squat!

Further,

According to studies noted in the book “only 2% of moisture “walks” through the breathable wall. Not much but enough to allow moisture that does enter find its way out. This is because they allow moisture to move into and then out of a wall without causing mold growth or structural damage. At the same time they provide the one thing you would not expect from a porous, low density wall structure, excellent thermal performance. The latter is possible because unlike infiltration (between and through materials) diffusion is slow and therefore so is the rate of heat transfer especially in thick mass walls (lag time, referred to as heat capacitance) that dry moisture out.

“The thing that I get asked about most is condensation of water vapor as it travels through an assembly and the interstitial moisture left there”

This will not occur in a properly designed breathable wall as noted above. There will be no " interstitial moisture left there" or in the wall since it will dry out from heat capacitance based on "lag time" or move out of the wall. Your comments on RH and moisture regulations or coupling between the inner wall and interior conditioned air that depend on relative humidity agree with the authors, however, materials such as clay will have a higher adsorption or regulatory function since the pore structure is larger compared to drywall or a material the has smaller pore structure or micron sizes less than .002 like plastic.

“I don't think we want much water vapor to walk through the walls, but we do want to hold it up and let it back into the home in order to maintain proper indoor RH.”

Correct, as noted above very little “walks through" (less than 2%) and the amount that does gets dried out or leaves the wall if the design is correct.

There are some charts and graphs that include lime and gypsum plasters I’ll post soon that will clear all this up.

Thanks again for the comments, it makes me go back over the material so I can get it

Another thing to keep in mind is this book focuses on mass not stick built, batts or loose filled wall cavities with drywall and sheathing, where multi-dimensional convective air loops and temperature fluxes are fast to react, or r-values are degraded by moisture. Mass walls and natural materials are less understood , moisture does not degrade some mass walls thermal properties, hence the focus of this book.

Today's lessons ....Bill take note "EMC is more dependent on RH, less on temp" .... If your adobe clay brick is unfired it is looking good!

I'll look at Durisol closer next and then how adsorption and hygroscopicity applies to the building envelope.

I find it interesting how clay surpasses materials in EMC and how the manufacturing industry does not provide EMC in their data sheets or adsorption speeds. Now take a look at strawbale/plaster assemblies that have these properties and need no plastic or "barriers" ....

Here is some strawbale research by John Straube for another perspective on what has been discussed thus far...http://www.ecobuildnetwork.org/images/PDFfiles/Straw_Bale_Test_Downloads/moisture-properties_of_plaster_and_stucco_for_strawbale_buildings_straube_2003.pdf

Some extracts on permeability/diffusion, hygroscopic adsorption/absorption.....capillary is discussed and upcoming.

Surfaces in contact with water vapour molecules have the tendency to capture and hold water molecules because of the polar nature of the water molecule; this process is called adsorption. Most building materials are porous and have very large internal surface areas. For example, brick typically has an internal surface area of from 1 to 10 m2 /g, cement paste from 10 to 100 m2 /g, and wood, straw, or cellulose can have even larger surface areas. Therefore, as water vapour molecules adsorb to the internal surfaces of these materials, the materials' water content increases significantly, and the materials are then described as hygroscopic . Materials such as plastic and steel do not have internal pores and therefore are not hygroscopic -- they do not pick up moisture from water vapour in the air.

As the relative humidity increases, the moisture content of porous materials increases because more of the vapor in the air adheres to the materials’ pore walls. When the RH exceeds about 80 to 90%, liquid water begins to form in the smallest pores, and eventually in the larger pores.

The relationship of air relative humidity to moisture content is called the sorption isotherm and is unique for each material (Figure 1.1). It may take weeks or months for a thick solid material to reach equilibrium with its relative humidity environment.

When a material has adsorbed all the vapor it can from the air (e.g., the moisture that a material will adsorb when left in a 100%RH room for long enough), further moisture will be stored in the pores and cracks within the material by capillary suction, or by absorption. Only when all pores are filled with water is a material capillary saturated. For example, wood (and likely straw) will adsorb vapour from the air up to approximately 25% moisture content at 98% relative humidity, but fully capillary saturated wood may hold two to four times this amount of water. Once a material is capillary saturated it will generally not be able to store any more moisture. Hence, when this moisture content is exceeded, a material is called over-saturated, and drainage, if possible, will begin to remove the excess moisture.

(Dale, so it appears wood is good internal mass from a moisture standpoint if it has a way to dry out fast)

Graph 1 below: You can see the number of tick marks increase at the end of curve indicates saturation in the graph below.

"The capillary transport properties of strawbale have also not been measured. While the walls of the stalks will wick liquid water (because of the nature of the small cellulosic walls), the bale itself is composed of mostly large pores which will not wick water. Therefore, the water uptake of a strawbale will be slow, and should quickly reach equilibrium with drying. In general, liquid transfer of the straw has no practical importance since liquid water should not be allowed to contact strawbales. "

The way I interpret that as related to what has been discussed so far is due to slow movement of heat through the assemble/mass of the bale as a whole (not the straws themselves) and their ability to store such high levels of moisture safely, capillary(wicking) uptake will dry itself out before reaching a saturation issue. We still do what we can to keep bales from contacting water, but small cold condensations on cold concrete or rubble trench do not need a barrier like alot of folks are using for wood sill plates, sheathing, etc.

This validates the low impact of temperature on EMC....See graph #2.

2.1.3 Moisture Storage
The moisture storage (sorption isotherm) of grasses and straws is of some interest to agricultural engineers. It has been studied by many. Plots of some
of the data from Lamond and Graham [1993] are presented in Figure 2.1. It can be seen that the sorption isothem is little affected by temperature (hence
the term isotherm) and that the curve is similar to that of wood. That the response of straw, grass, and wood are similar is expected because of their
similar cellulose and lignin microstructure.

You can read about renders or skins in the test results, graph 3 below, and the large increase in permeability by adding lime (less portland cement) yields "the highest permeability" as well as the high perm of untreated earth plasters is interesting.....We want high perm of skins so moisture can access the large pore "storage" structure of clay, straw, type materials, and dry fast. Linseed oils and lime washes on earth plasters drops the permeability, linseed oil more 20%, lime wash 3-5% unless 5 coats where applied then equal to untreated earth, also adding 10-50% lime does not lower perm rating of untreated earth plaster.

Capillary (wicking) of stuccos shows earth plasters to be less absorbent and have a higher ability to manage wetting (adsorption, EMC) than less-porous cements or roughen, sanded troweled surfaces as Bill renders are less absorbent from wicking..Siloxane (polymer surface sealer) reduced absorption the most, coats of lime plasters next (keeping in mind that lime washes also increased permeability). Adding lime to earth plaster increases water absorption, Perhaps the addition of several coats of lime wash would reduce the absorption.

Conclusions of interest...

1. Earth plasters are generally more permeable than even lime plasters. The addition of straw increases the permeability further. A 38 mm (1.5”) thick
earth plaster can have a permeance of over 1200 metric perms (over 20 US Perms), in the same order as building papers and housewraps.

2. Applying an oil paint to a moderately permeable 1:1:6 stucco will provide a permeance of less than 60 metric perms (1 US perms) and thus meet the
code requirements of a vapour barrier. ( in most cases natural materials do not need a barrier)

3. Earth plasters were not found to have significantly different water absorption than cement and lime stuccos. The earth plasters, regardless of
density and straw content, resisted 24 hour of constant wetting easily, although the topmost 1/8” of surface became quite “muddy”. In a real
rainstorm this behavior may cause erosion. (hence the need for a good drainage plan).

4. Lime washes appear to be somewhat useful for reducing water absorption while not reducing vapor permeance. The lime wash over earth plaster did
not dramatically lower water absorption but will increase the mechanical strength of the plaster after wetting, i.e., they will increase the resistance to
rain erosion.

5.Based on Minke’s and Straube’s earlier tests, siloxane appears to have little or no effect on the vapor permeance of cement, cement:lime, lime, and earth plasters while almost eliminating water absorption. The use of siloxane can be recommended based on these earlier tests. (better than lime per report..they make low VOC)

6. Linseed oil at 2% in an earth plaster mix is not a very effective water repellent and does act to restrict vapor permeance somewhat. It may add
some strength to an earth plaster in the wet state. Heavy applications of linseed oil to the surface of finished earth plaster will, based on Minke’s
tests, reduce the water absorption to almost zero, but will markedly decrease vapor permeance. (not good for breathable walls)... I wonder about wood?

7. The test methods described here appear to provide repeatable results, and in general compare well to previous tests on different samples by both the
same (Straube) and different researchers (Minke). (I have worked in test labs before, this test looks legit for some basic design guidelines)

More data.....

Awesome info Terry!

It will take me a while to digest all of this, but I wanted to share this clay plaster photo. We were out of town with a young lady watching our place who watered the plants a little too much. She must have seen the streak on the wall where the water had soaked in and wiped it up with a towel, taking the hand-dug micaceous clay plaster with it.

I've been experimenting with mixtures of clay, lime and gypsum to shore up the shortcomings of each.

Yes, I agree with this logic as the ultimate in wall assemblies.

1) utilize highly permeable materials
2) reduce capillary absorption with permeable skins that have a reduced capillarity either by treatment (siloxane or lime wash) or by mechanical burnishing/sintering
3) use materials that can hold a lot of moisture without damage, have a high EMC
4) this one I am adding myself, use materials that get stronger with time or at least age gracefully

I have a thermal imager, so I got it out at my house to show thermal drive and temperature profile across a thermal mass wall.

The wet fingerprints were 2 different sets since I took too long getting out the imager and the first ones had dried out already.

Then here's a close-up of the adobe wall; you can see there is a small gap between each wythe.

Then lastly a lime skin. This coating is highly permeable, but will slow the adsorption of water vapor from the air by nature of the closed off pore structure that has been accomplished through heavy burnishing and in this case, a small amount of natural soap. Even so, there are areas that have larger pores and therefor higher capillarity, these are the areas with less shine.

BTW Terry, you are the recipient of my very first apple.

Bill, I'm guessing the thing to do when clay plaster gets wet is let sorption do it's thing. I struggle finding a sealer that makes earth (plaster, rammed earth, etc) less friable in the US, there all over in Europe. I tried a spray lime wash like 7-8 coats through an agriculture spray pump at 50-50 lime/water ratio on rammed earth to a point where I could brush coat it thicker...Did ok until I hit it with vacuum, or a kid beating on walls would not be good. You can pigment it but loose the beauty of the rammed earth striations. I tried an acrylic sealer that went on white and dried clear to a satin natural look, also available in semi and gloss....better....I wonder if that Siloxane do the trick? It is very low voc, 100 % permeable, few choices of products on the market, and siloxane sounds great it gets the surface pores to manage liquid water and allows the wall to breath.

How are you burnishing the lime? I talked to some lime manufacture chemist when I was developing a hemp binder that told me gypsum is used as a filler to cut cost, does nothing chemically to the calcium and/or magnesium oxides in lime. What is the gypsum doing in your mix? You say you put it down first as a base then a burnished lime finish?

Nice seeing first had the pics of different natural pore sizes, great stuff!

Thanks for the apple btw

Terry Ruth wrote:Bill, I'm guessing the thing to do when clay plaster gets wet is let sorption do it's thing.

Yeah, the downside of clay is that it turns back to clay when wet. When I took out the upper half of that wall, I threw the bricks outside; 2 rainstorms later they were a pile of mud! The upside is I have some leftover clay that I dried into little bricks for patching; wet it and it replasters, super easy.

Terry Ruth wrote:I struggle finding a sealer that makes earth (plaster, rammed earth, etc) less friable in the US, there all over in Europe.

European architecture has always been a couple of steps ahead of American architecture. Especially in the field of historic restoration, which can be completely undone by a lack of breathability like the many historic masonry homes around here that receive a full spray latexing. So, sealer is probably the wrong word here, maybe consolidant? If you look closely at the adobe photo, you can see little bits of lime. The plaster skin on earthen architecture plays a very important role in eliminating shear stress during earthquakes. You can see that the guys who built my place used a good inch of lime render, on wire lath on the edges and corners only, same with the outside. This place has withstood 2 major earthquakes already!

Terry Ruth wrote: I tried a spray lime wash like 7-8 coats through an agriculture spray pump at 50-50 lime/water ratio on rammed earth to a point where I could brush coat it thicker...Did ok until I hit it with vacuum, or a kid beating on walls would not be good. You can pigment it but loose the beauty of the rammed earth striations. I tried an acrylic sealer that went on white and dried clear to a satin natural look, also available in semi and gloss....better....I wonder if that Siloxane do the trick? It is very low voc, 100 % permeable, few choices of products on the market, and siloxane sounds great it gets the surface pores to manage liquid water and allows the wall to breath.

Once lime fully carbonates, it is quite durable and because of the refractive nature of the crystalline structure, it radiates a faint glow around it. I don't know anything about it, but Siloxane doesn't sound long term to me.

Terry Ruth wrote:How are you burnishing the lime?

Typically with a steel trowel and then finishing the carbonation process by rubbing with a wet grout sponge.

Terry Ruth wrote:I talked to some lime manufacture chemist when I was developing a hemp binder that told me gypsum is used as a filler to cut cost, does nothing chemically to the calcium and/or magnesium oxides in lime. What is the gypsum doing in your mix?

The gypsum allows for a set, so I don't have to keep wetting and rubbing the surface of the plaster. If you don't "babysit" lime, it won't carbonate and the surface will craze and powder, this often takes longer than the actual plastering.
I guess I also use it as an aggregate for finer finishes like inside a fancy house. A setting aggregate that supports the CaOH as it transforms back into CaCo3. Gypsum typically has less embodied energy than lime, since it is fired at 350F for a few hours vice lime 1300F for 24 and clay is not fired at all. I think the best plaster is a mix of mineral plasters, pozzolans, fibers and aggregates appropriate to your own bioregion and sourced as locally as possible.

Terry Ruth wrote:You say you put it down first as a base then a burnished lime finish?

I do this because I have a lot of wall to cover and gypsum is sandable and sets quickly. I think it's too soft by itself, so I cover it with lime wash or veneer plaster, but you could use a natural paint at this point. This was common practice for 100 years here in the west; other places, I don't really know.

Terry Ruth wrote:Nice seeing first hand the pics of different natural pore sizes, great stuff!

Thanks, here's a photo from our B&B restoration; kind of hard to see the glow in photos, but trust me, it's real.

Bill, I tried to burnish lime with a wood trowel to get a feel from what you are talking about, very interesting how it changed the surface.

Back to breathable walls book.

A recap: There are many view points on the topic of breathable walls. This book defines them as having to meet three physical requirements to produce healthy construction,

1. Permeability and diffusion (discussed). Main point: Defy's commonly accepted logic & modern building techniques which use only permeability as a metric (or "perm rating", or Class of vapor barrier-retarder depending on perm rating). This is because moisture is allowed in small amounts to move in and out of the wall without causing rot and at the same time excellent thermal performance (slow moving heat transfer dries out moisture) by use of thick massive walls that also remove vocs (best to not introduce).

2. Hygroscopic desorption/adsorption (discussed). Here adsorption or EMC (Equilibrium Moisture Content) is a property of regulating moisture content at the surface and a drying speed (< 48 hours to prevent mold, large pore capacity clay being high in H2O or EMC adsorption capacity). EMC is primarily dependent on relative humidity (RH), not temperature, which challenges a common myth that only cold condensation creates mold. If you look at the table above Durisol (cement-bonded wood-fibre ICF boards) performed well over a wide range of RH, brick performed poorly until it reached 90% so it would not be characterized as a hygroscopic. Lime and cement plaster not much better-modest. Buildings are typically in the 50-85% RH range. Speed of adsorption is critical, although cements (portland based ) have moderate EMC that are very slow to adsorb and dry causing mold.....un-fired clay very fast. Likewise, spruce fast along the end grain, slow across. Modern building's fail to consider this property. Key point is some materials can regulate relative humidity better than others, from the environment, cooking, showers, etc, indoors and weather outdoors. Studies have shown that 50% +/- 5 RH can be regulated without the use of air conditioning. Some modern methods that dry inward rely on cooling, whole house dehumidifiers.

3. Capillary adsorption/absorption (not discussed)

We also seen surface finishes such as linseed oil take water absorption almost down to zero like a plastic barrier does but, drastically reduce permeability we want high for breathable walls. I’ll assume the same for woods, oils block pores good for water proofing, bad for EMC or adsorption. Linseed oil at 2% "in" an earth plaster mix is not a very effective water repellent and does act to restrict vapor permeance somewhat. It may add some strength to an earth plaster in the wet state. Heavy applications of linseed oil to the surface of finished earth plaster will, based on Minke’s tests, reduce the water absorption to almost zero, but will markedly decrease vapor permeance.

So what we see at the surface with the naked eye does not necessarily equal what is happening at the pore structure chemically.

Siloxane on earth plaster performed well both as a water barrier that did not reduce adsorption or permeability.

Water and moisture management are two different things, air yet another. Some materials manage them all better than others. The smaller the pore size the better as a water barrier, larger moisture regulator, except the exceptional materials such as clay, wood, durisol, siloxane, that do both. The new term is moisture “regulator” not to be confused with barrier like plastic provides. The key is not having food, moisture, and temperature for fungi growth.

Lime washes appear to be somewhat useful for reducing water absorption while not reducing vapor permeability. The lime wash over earth plaster did not dramatically lower water absorption but will increase the mechanical strength of the plaster after wetting, i.e., they will increase the resistance to rain erosion.

Lime washes on plasters may work well, but rammed earth a white wash hides striations Siloxane clear coat may be better. Burnishing lime provides more surface durability without affecting absorption/adsorption.

Closer look at Durisol next.

http://durisolbuild.com/insulated-concrete-forms.shtml/

Durisol does not burn or melt. This is not the case with Styrofoam and other ICF products. The smallest Durisol wall has a 4 hour fire rating, zero flame spread, smoke spread of 11 and no black smoke or toxic fumes created in the event of a fire.

Durisol is more energy efficient. The insulating thermal mass/dynamic effects are better with Durisol than other ICF systems because with Durisol, the insulation is placed primarily on the exterior of the concrete mass. Polystyrene ICF foam blocks put 50% of the total insulation on the interior, which actually prevents the transfer of heat/energy between the concrete mass and the interior conditioned space. With Durisol, all insulation inserts are positioned towards the exterior, where it should be, to maximize any thermal mass gains.

Durisol facilitates improved indoor air quality. The Durisol material is a hygroscopic material – which means that it has a very large capacity to store and release moisture as required, depending on the environmental conditions. This storage capacity refers to storing moisture in the form of water vapor and increased material moisture content – not liquid water. Also, the Durisol material and wall system is extremely vapor permeable. It does not act as a vapor barrier, but acts as a vapor regulator and keeps indoor RH (Relative Humidity) levels at a healthy and comfortable level. We have conducted full scale wall tests and have proven that Durisol does not allow condensation within the wall cavity when used without a vapor barrier, and maintains RH levels below RH 65-70 naturally.

Durisol promotes healthy indoor environment and inhibits mold growth. Firstly, because the material is hygroscopic and vapor permeable, RH levels are kept low enough such that it is not possible to reach the level of RH where mold can start to grow (typically 70% RH). Combined with the high pH (alkaline) environment resulting from the cement content, this means that the wall system actually helps to inhibit mold growth.

http://durisolbuild.com/iaq.shtml/
This Durisol paper has data that supports what the book presents. Note the health related issues and percentages by the EPA. The importance of regulating indoor IAQ, RH and PH (< 10). Also, drywall paper a mold food source. Remember mold can always be seen.
Looking at the graph above Durisol adsorbs to ~70 % RE than slows down, others have little to none adsorption until 60-90% then slow down adsorbing little. One could expect strawbales that are high perm and hygroscopic to perform the same.

This is interesting,

“Exclusion is the third principle of good IAQ design. Radon control, for example, requires an airtight floor and/or basement system. Exclusion of radon from the interior environment must be a serious design consideration because of the serious consequences of exposure. Ventilation of living areas (i.e., removal) does aid radon control, but it is imperative to first design and build the ground floor or basement as airtight as possible to avoid penetration into the building.Exclusion of outdoor particulates requires an airtight above-grade building envelope. If the air barrier system is applied to the interior side it can control off-gasing, particulates, and mold spores from within the enclosure system. “

And this,

The Systems Approach
None of these principles can provide indoor air quality on their own: a holistic approach is necessary. Avoiding materials which offgas is a useful and necessary approach, but ventilation, air barriers, humidity control, and high surface temperatures working together can provide much better IAQ than either approach used independently.

And this summary of perm and hygroscopic…can anyone pronounce ” Atmungsfaehig” ?

” Atmungsfaehig” or Breathable Walls

” Breathing” walls are often recommended by designers of healthy housing, especially by those who study and practice Baubiologie, but the term itself is used in an imprecise manner in the English language. A review of the lay literature shows that there is considerable confusion about what constitutes a “breathing” wall, and how they work to improve IAQ. Although “breathing” implies airflow, this is not necessarily the case. In much of the scientific literature, the term simply means that a material or assembly is both open to vapour diffusion and hygroscopic. In essence, this combination of properties allows a significant amount of water vapour (and other gases) to be adsorbed and released quickly, thereby regulating the room climate and hence indoor air quality.

Although other gases will also diffuse through walls (exchanging CO2 and oxygen for example), water vapour is one of the primary determinants of a healthy room climate and, as such, is often the primary gas that breathing walls are designed to adsorb. In most healthy houses built using the principles of Baubiologie, the design of the enclosure and interior partitions is based on ensuring water vapour breathability (Krusche et al 1982, Kuenzel 1980).

Interesting position on allowing air to pass through walls,


” Air open” or “dynamic” walls that allow slow and controlled airflow through them are considered by some to be the ideal breathable wall. Research, however, does not support this contention (Kuenzel 1980). While several dynamic wall houses have been built in Canada (Timusk 1987), and Sweden (Levon 1986) such houses require special design and all successful dynamic wall homes have used mechanical means to provide the required level of ventilation flow control. The design goal of these houses is usually a reduction in conductive and exfiltration energy loss (which they can achieve). They do not necessarily improve IAQ, other than by ensuring good ventilation (Taylor et al 1997).

Thermal performance about that of well-designed clay-slip,
Durisol with a dry density of 500 kg/m3 (30 pcf) has a thermal resistance is about RSI7.0 per m, (R1.75 per inch).

This is real interesting charting below, look how poorly slow painted drywall and modern walls perform. Note how well and fast Durisol and strawbales perform, and some believe strawbales do not perform that well when subjected to water and moisture.

Dynamic Hygric Response ( a new term I rarely see being discussed) I like it!

A recent multi-year study concluded that short-term RH peaks of a buildingís air can support fungal growth, even though the average conditions are well below the threshold for fungal growth, e.g., 70 to 80% RH (Adan 1994). For example, the simple act of boiling water for cooking creates a significant short-term rise in humidity near the kitchen. After the interior RH has dropped, the fungi can continue to grow for some time using moisture stored within the fungi.

The speed with which a wall surface can absorb moisture is important for avoiding surface condensation and surface relative humidities required to support fungal growth. Materials with a combination of the properties of vapour permeability and high hygroscopicity allow that material to quickly moderate humidity variations by storing or releasing significant quantities of water vapour. A vapour tight finish on walls allows the surface relative humidity to climb to the level where fungal growth can be sustained.
If a material can quickly adsorb moisture from the air, this material will maintain the RH at its surface at a lower and more stable level while also moderating short-term interior air humidity variations. The dynamic hygric response of several wall systems was studied with the aid of computer modelling and field measurements. The results are presented below.

Modelling Hygric Response

Using a sophisticated computerised finite element package (developed by Kuenzel, 1997) the amount of moisture released into a room by several different wall systems was calculated. The program is one of the most advanced in the world (it considers different moisture diffusivities for suction and redistribution, surface diffusion, capillarity, vapour diffusion, etc.).

Each of the assemblies modelled comprised a 200 mm layer of material. Some of the walls were finished with lime plaster, others with gypsum drywall and various paints. Material properties were taken from manufacturerís data and various sources (ASHRAE 1997, IEA 1997). The simulation considered a wall and room initially at 30%RH followed by an instantaneous rise in room air moisture content to 80%RH. Over the period of a week the simulation calculated the water vapour balance every 15 minutes.

Figure 3 plots the moisture adsorption of four walls for the first 24 hours. All of the systems responded in a similar manner, but the speed of response differed considerably. The initial response was fast, followed by a slow exponentially decaying period. Because the shape of the response curves are similar, the results can be usefully summarised and wall systems approximately ranked: see Table 1.

Table 1 shows that there is a large difference between the behaviour of some common wall systems. The plastered Durisol insulated concrete form system and strawbale wall provide about 8 times more vapour control to the indoor environment than the walls used in a typical modern home, and 25 times that of a modern motel room with vinyl wall paper. While the above results do not attempt to exhaustively rate each assembly (the more complex discussions and calculations necessary for this are beyond the scope of this paper), it does provide a relative ranking which clearly shows the problems associated with the use of the most common modern building systems.

The simulation results also showed the clear superiority of lime-based plasters over pure cement-based plaster. The hygroscopic and highly vapour permeable nature of lime plaster provides a very fast response (i.e., several minutes) to changes in the vapour content of the interior air. Substrates like Durisol, strawbales, and brick provide much more moisture storage, storage which participates at longer time scales (i.e., several hours). The worst possible finish is a high-grade vinyl wall, which not only off-gases VOCís but also returns vapour adsorption values of less than about 10.

This explains why modern building materials and ventilation alone fails, Field study next this stuff is mind boggling but I'm glad I am learning it

Thanks for breaking this all down here for us Terry!

Some really good stuff here.

I started a thread about usingnatural plaster instead of polyethylene to keep a wofati/psp type building dry. Check it out, see if you have anything to say on that subject.

The affect of temperature on materials seems to be a confusing topic so I thought I'd have a closer look:

Moisture sorption isotherm – a curve giving the functional relationship between humidity and equilibrium water content of a material for a constant temperature.

This graph below shows how little effect temperature (-10c/14f-50c/122f) has on moisture storage in a wall material such as cellulose, wood, grass, perhaps explaining why we cannot control this storage rapidly by turning the heater or AC on. Note the increased fast spike in storage between 90-100% relative humidity (RH). That has to do with a combination of storage and capillary saturation. Once the materials pores, cracks, are saturated it will drain if it can to remove excess moisture.

Some that subscribe to walls and ceilings with an outer moisture vapor barriers such as plastic or water and ice(W&I) shield on a roof with low permeability and ability to store attempt to “dry inward” need to control indoor humidity with mechanical devices such as whole building dehumidifiers like the ultra-air SD12: http://www.ultra-aire.com/products/dehumidifiers/ultra-aire-sd12. The problem with this theory is the humidifier is not smart enough to understand the material properties such as moisture storage capacity of the wall, drying speed, EMC, permeability, capillary action, saturation, etc, and that control is in the hands of the occupants.

Vaulted SIPS with a water and ice barrier on decking, cladded with a metal roof would be an example, or, ZIP sheathing system of sheathing and taped seams that create a non-insulated outer barrier that can cold condense (not to be confused with a moisture storage or regulating material surface that is mainly dependent on relative humidity as show in the graph, not temperature) which a barrier like W&I, ZIP, or house wrap does not provide. If ZIP tapped system, W&I, house wrap, were added to the graph the MC would be very low and flat (horizontal) over the RH range. Then if you added temperature and graphed the effect you would see MC rise especially due to cold condensation. That is why it is reliant on an insulation and temperature control more than a hygroscopic material such as wood, clay and lime renders because these small pore materials lack MC or a molecular structure that can store large amount of water vapor. Add to that the food they carry for fungi (fire retardants, UV additives, resigns, oils, ) and it will not take long once moisture condenses on these materials to create fungi. That is why we see this battle between ZIP and Dupont house wrap: pdf download

“Wall system drying: To meet minimum vapor permeable WRB requirements, the WRB must have a vapor permeance of at least 5 perms, as tested per ASTM E96 B (desiccant method). Third-party laboratory testing of the vapor permeability of ZIP System® wall sheathing shows that it has vapor permeability less than 1 perm, under both wet and dry cup measurement conditions. Because ZIP System® wall sheathing requires all seams to be sealed with tape, installed ZIP System® wall sheathing constitutes an exterior, non-insulated vapor barrier. As such, it can be subject to condensation during cold weather. An exterior vapor barrier significantly reduces drying capability of the wall system if moisture enters through any mechanism. In contrast, current DuPont™ Tyvek® WRBs have permeability ratings ranging from 20 to 60 perms. This high permeability allows the wall system to maintain a higher drying capability than wall systems utilizing ZIP System® wall sheathing. “

If you ever read the wet and dry cup perm test (50-100% RH) you see it is very limited testing and what these companies are fighting over, it does not test for the other two requirements for hygroscopicity (EMC, drying speeds, saturation) and capillary adsorption/absorption. It does not focus on 75-100% RH and drying speeds to outside air of moderate humidity 75% under normal conditions of interest. Interesting how these manufactures do not promote how they meet the criteria of being “hygroscopic” like simple all natural clay and wood you find in your back yard that store, regulate moisture, better, not condense it at it's surface.

Anyone see it differently please explain.

Edited by moderator to fix link

A different yet same application with wood. It's drying direction is quite complex. Today's solution glue it down and call it "Engineered Wood"


About Moisture and Wood

The durability of wood is often a function of water, but that doesn't mean wood can never get wet. Quite the contrary, wood and water usually live happily together. Wood is a hygroscopic material, which means it naturally takes on and give off water to balance out with its surrounding environment. Wood can safely absorb large quantities of water before reaching moisture content levels that will be inviting for decay fungi.

Moisture content (MC) is a measure of how much water is in a piece of wood relative to the wood itself. MC is expressed as a percentage and is calculated by dividing the weight of the water in the wood by the weight of that wood if it were oven dry. For example, 200% MC means a piece of wood has twice as much of its weight due to water than to wood. Two important MC numbers to remember are 19% and 28%. We tend to call a piece of wood dry if it is at 19% or less moisture content. Fiber saturation averages around 28%.

Fiber saturation is an important benchmark for both shrinkage and for decay. The fibers of wood (the cells that run the length of the tree) are shaped like tapered drinking straws. When fibers absorb water, it first is held in the cell walls themselves. When the cell walls are full, any additional water absorbed by the wood will now go to fill up the cavities of these tubular cells. Fiber saturation is the level of moisture content where the cell walls are holding as much water as they can. Water held in the cell walls is called bound water, while water in the cell cavities is called free water. As the name implies, the free water is relatively accessible, and an accessible source of water is one necessity for decay fungi to start growing. Therefore, decay can generally only get started if the moisture content of the wood is above fiber saturation. The fiber saturation point is also the limit for wood shrinkage. Wood shrinks or swells as its moisture content changes, but only when water is taken up or given off from the cell walls. Any change in water content in the cell cavity will have no effect on the dimension of the wood. Therefore, wood only shrinks and swells when it changes moisture content below the point of fiber saturation.
Like other hygroscopic materials, wood placed in an environment with stable temperature and relative humidity will eventually reach a moisture content that yields no vapor pressure difference between the wood and the surrounding air. In other words, its moisture content will stabilize at a point called the equilibrium moisture content (EMC). Wood used indoors will eventually stabilize at 8-14% moisture content; outdoors at 12-18%. Hygroscopicity isn't necessarily a bad thing - this allows wood to function as a natural humidity controller in our homes. When the indoor air is very dry, wood will release moisture. When the indoor air is too humid, wood will absorb moisture.

Wood shrinks/swells when it loses/gains moisture below its fiber saturation point. This natural behaviour of wood is responsible for some of the problems sometimes encountered when wood dries. For example, special cracks called checks can result from stresses induced in a piece of wood that is drying. As the piece dries, it develops a moisture gradient across its section (dry on the outside, wet on the inside). The dry outer shell wants to shrink as it dries below fiber saturation, however, the wetter core constrains the shell. This can cause checks to form on the surface. The shell is now set in its dimension, although the core is still drying and will in turn want to shrink. But the fixed shell constrains the core and checks can thus form in the core. Another problem associated with drying is warp. A piece of wood can deviate from its expected shape as it dries due to the fact that wood shrinks different amounts in different directions. It shrinks the most in the direction tangential to the rings, about half as much in the direction perpendicular to the rings, and hardly at all along the length of the tree. Where in the log a piece was cut will be a factor in how it changes shape as it shrinks. One advantage of using dry lumber is that most of the shrinkage has been achieved prior to purchase. Dry lumber is lumber with a moisture content no greater than 19%; wood does most of its shrinking as it drops from 28-19%. Dry lumber will have already shown its drying defects, if any. It will also lead to less surprises in a finished building, as the product will stay more or less at the dimension it was upon installation. Dry lumber will be stamped with the letters S-DRY (for surfaced dry) or KD (for kiln dry).

Another way to avoid shrinkage and warp is to use composite wood products, also called engineered wood products. These are the products that are assembled from smaller pieces of wood glued together - for example, plywood, OSB, finger-jointed studs and I-joists. Composite products have a mix of log orientations within a single piece, so one part constrains the movement of another. For example, plywood achieves this crossbanding form of self-constraint. In other products, movements are limited to very small areas and tend to average out in the whole piece, as with finger-jointed studs.

http://www.globalwood.org/tech/tech_moisture.htm

It's not clear to me how finishes affect hygoscopicity and drying of wood. Here is a quote from Jay,

Jay C. White Cloud wrote: I have Douglas Fir and White Pine both that has been outside for 8 years...Its as yellow as the day it came out of the shop. Then again, we use traditional treatments of pine rosin, beeswax, flax oil, tung oil, citrus oil and a little UV stabilizer that seems to all work great...Food grade on most of the materials we use. All are classified as naturally and safe...including the fire retardant we sometime have to apply for frames that are in "high risk flash zones."

Seems to me no finish if the interior walls had clay plaster as in a post and beam and strawbale wrap, or other similar type of material that keeps wood below fiber saturation. The outside timbers one of Jays secret potions?

http://www.greenbuildingadvisor.com/blogs/dept/qa-spotlight/why-it-so-humid-here

Here is an example of a recent SIPs constructed home where the foam and assuming taped impermeable joints, along with a barrier under the slab have vapor locked moisture into this home and the home owner can not understand why it is so humid and uncomfortable. The "experts" conclude that construction humidity is the culprit " wait a year, use a dehumidifier to dry it out". Wow! In less that 48 hours studies have shown that mold and fungi can develop to a point of no return and they want to wait a year? SIP alone has enough food for fungi (fire retardants, blowing agents, etc).

They also think the concrete will eventually dry out and solve the issue. We seen by the studies above that concrete has low permeability and diffusion (ability to dry, transport moisture, and it is not free draining). Even if it could dry to the dry ground it can not due to the barrier underneath the slap and footing. Drying to the inside is dependent on indoor RH and very slow as seen by the graph they posted. The proper material under the slap would satisfy the three transport conditions we discussed, diffusion, hygroscopic (ability to regulate), and drainage (capillary) plastic barrier do not provide. A limecrete would satisfy this, or rock. If the indoor RH stays high due to wall, roof, barriers, which is this case, the dehumidifier will still be required for the life of the building since this design has no way to dry out, only in.

The SIP walls and roof: EPS or any foam is impermeable, OSB low perm, slow draining, and the orientation of the panels can trap moisture in between joints.

Had better materials been used and the walls/roof/building were capable of a vapor and air xchange every ~50 hours(walls), (building 1 ACH, Air Changes/hour) or so along with a natural ventilation plan this would not be the case. The ERV (active air xchanger) can potentially exchange more humid outdoor air making it worse unless if can dehumidify alone (unlikely, especially in high humidly climates)...The ERV and the dehumidifier need to understand the wall RH humidity content and dry it out fast! (unlikely).

What amazes me is John Straube these experts look to for advice for one, author of this book (George Swanson) has data to support this we have been looking at above, they ignore, or, have no idea it exist (unlikely). I guess clay plaster and stucco, lime, Durisol, does not bring in the bacon Selling dehumidifiers, ERVs, barriers, toxic SIPs are more profitable to sick building's that can cause injury.

Durisol or MGO SIP would perform better.

Capillary Absorption/desorption: Defined as the physical process involved with the flow of water through pores within a material. The degree of capillarity is determined by the balance between forces of surface tension, adhesion, gravity, and pressure. The rise can be tens of feet to miles, molecular attraction between solid and liquid molecules can be very strong. A tree would be an example, likewise, in buildings from the water table through soil through the foundation into the home (book gets into foundations later).
“Capillary breaks” stops the uptake (which does not have to be up it can be any direction like a sponge). Traditionally, courses of copper, tin or lead, or solid slate. Today, lots of coating’s and foam products that are impermeable to stop it dead in its tracks.

Materials that drain well are also said to be “capillary open” due to large pore sizes. Pore sizes have to be larger than that needed for vapor transport since this is liquid state, so water has to be present for it to occur. Voids (cracks) in homogenous materials are also a good path. Ventilation gaps behind cladding and sheathing are considered a capillary break since air flow counteracts the action or causes evaporation or drainage, but, they are designed in gaps by designer’s not material properties.

There is little data on the uptake of water by wetting or “water absorption coefficient” available. John Straube has some data in this strawbale doc: Measuring it, there is no standard, also obscure. No rules on whether we want high or low. http://www.ecobuildnetwork.org/images/PDFfiles/Straw_Bale_Test_Downloads/moisture-properties_of_plaster_and_stucco_for_strawbale_buildings_straube_2003.pdf Also, Neil May of Natural Building Tech, UK. CANADA M&H Corp.

See below: The materials towards the top that free drain are preferred since they drain fast and evaporate for vapor diffusion we discussed earlier.

In buildings the main source is rain water. To control it from being trapped within a homogenous materials there are four strategies. See below.

Like hygroscopic adsorption, capillary absorption is reversible but, adsorption and desorption may occur at significantly different rates. Two examples are, construction materials get wet and are not allowed to dry, or, materials are mated that do not allow drying. If capillary is small, when it gets wet it may be too slow to dry, and visa-versa. Therefore, breathable walls prefer (but not always) the first two approaches, using materials having high degree of capillarity or ones that are free draining. (Note: Portland cement is high but not recommended). Large masses of concrete are slow to dry since it starts out with completely liquid saturated, slow even when cured, pores hold onto water.

Straube’s Data below, the results of the uptake tests were not very consistent or repeatable in the case of the lime and cement stuccos. The earth plasters were remarkably consistent, exhibiting a coefficient of variation of only 3 to 6%. The earth plaster samples were remarkably consistent, and low absorption. Minke found his earth plasters to be twice as absorptive (0.152) although this range of material property must be considered normal in earthen materials. There was a slight trend toward lower absorption with increasing earth plaster density.

Surface finish…troweled for example produces more closed pores so absorption is lower, especially the lime and cements. It was observed that the earth plaster samples developed a wet, muddy, skin soon after contacting the water (within 30 minutes). The samples were remarkably tolerant of wetting however. The lime washed earth plasters remained firm even after 24 hours in contact with water. The lime plaster samples were by far the most absorbent.

In general, none of the coatings reduce water absorption to the remarkable degree that siloxane did in both Straube and Minke’s previous test. The best results were achieved by samples with coats of lime wash (which also exhibited high vapor permeance).

Lime washes appear to be somewhat useful for reducing water absorption while not reducing vapor permeance. The lime wash over earth plaster did not dramatically lower water absorption but will increase the mechanical strength of the plaster after wetting, i.e., they will increase the resistance to rain erosion. Based on Minke’s and Straube’s earlier tests, siloxane appears to have little or no effect on the vapor permeance of cement, cement:lime, lime, and earth plasters while almost eliminating water absorption. The use of siloxane can be recommended based on these earlier tests.

So here is proof that lime washes and siloxane can stop water uptake but allow vapor difusion, rendering “vapor barriers and retarders” (house and plastic wraps, petro-coating’s, etc) useless.
Straube’s Test Results: "It can be seen that the curves do not always exhibit a well defined slope as is typical of most porous materials. This is especially true of some of the lime and cement samples. This is likely because of the different surface treatments, e.g., a trowel smooth surface has a low absorption coefficient because the surface has closed cells."

Limecrete (rock, perlite, scoria, or other rock insulation) as a sub-slab vs plastic: Apply additional coats of lime wash and then burnishing or bull float the surface as Bill suggest makes it less absorbing to wicking water while also allowing high permeability for vapor diffusion and desorption for drainage. Applying lime to the sub-soil won’t make it less water absorbing but will strengthen its wetting strength just like it does earth plasters. That should help hold the lime surface together so that cracks do not develop in a lime/slab that wicking uptake will not occur. The compression strength and insulation r-value, coupled with the hygroscopic properties of lime-to-soil, vs plastic-to-foam-to-soil is far exceeding. Foam is 5psi compression at zero deflection and proper safety factor knock down with r-~1/inch . Limecrete 60-100 psi compression with r-1.5/inch depending on mix ratio. I’d start with 70% lime binder, 30% rock and sand. But, there is an added benefit for the lime due to one it does not contain any fungi food, two it is hygroscopic in managing water and vapor keeping it out of the slab. This way a wet slab can dry both directions, from gravity down when the ground is dry, or from ground pressure up wicking up to a storage area in the lime, not the concrete. From what I have seen a minimum of 2” thick lime, if close to a water table or wet lands make it 4”. The same will work for strawbale footings, or any footing or sub-slab. NHL 2.5 or Type SA(Aerated) lime.

That about concludes the discussion on the three methods of water and vapor transportation. I hope all following has learned as much as I have. There is a lot more coming up, I’ll keep posting. …thermal mass, radiant heat, radio frequencies, MGO, construction details (walls, foundations, roofs)…Excellent book so far I recommend highly!

Thanks again Terry for sharing this rare and extremely valuable information!

The only thing I would like to see is a full lime plaster assembly instead of just the 1:3 second coat.

Typically we embed the lath with a 1:2 coat, then straighten with a 1:3 coat and then apply a thin color coat with no sand, only pumice as an aggregate.

The difference in absorption is huge. I can just pour water into that 1 lime to 3 sand coat, but once the external 1 lime to 1 pumice coat gets wet, it will close up and shed water. This doesn't really come across in the lab, but it's readily apparent in the field.

Bill, yes very interesting informative book and you know what just baffles me is I have been told that "no measurable data exist" and these methods are controversial. There is all kinds of data that results from measurements above. So the next time someone claims that we can point them to this thread

The clay data seems consistent, lime varies with surface finish. 1:2, 1:3, them pumice/lime sounds great as insulating and water proofing with high perm. If the surface is burnished to close structure more of a water barrier is created if that what one wants, with the smaller the pore size. What mix of lime and pumice and what type lime are you using?

Where do I get pumice? Scoria" or other insulating rock that drains well? I know I can get perlite at Walmart in spring but it's a little expensive around here and large quantities, small bags to a job site does not seem very appealing.

Dursiol, has me a little confused. They have a very open pore, permeable, ICF form with excellent properties it appears but they support an exterior petro barrier and have no test results on the burnishing of lime you mentioned with their product, or other test results of natural barriers. From what I can tell at this time anyway by the data, that closed pore surface finish will produce a barrier and allow high permeability we want under slabs, exterior walls...or option 3 or 4 above. Durisol suggest a "parge coat" of portland cement/sand to close pores for stucco's on their product, cladding with vent gaps behind it. I need to call again and talk to an Engineer not sales....the book has more on Durisol later, which, if you wanted to take the manufactured product route for fast ease of construction looks to be one of the better ones. Far better than most SIPs. Don't let the lower r-value fool you, another myth discussed soon. What I figure is as George said (full breathable walls is not always desired) in some cases such as Durisol where the material has a high ability to store vapor on the interior side and prevent diffusion it to the concrete or to exterior barrier that does not have an ability to absorb or dry fast, then get trapped by an exterior barrier I question. My concern is if the warm humid inner wall saturates to the exterior barrier that does not allow drying to the outside if it is dry, purhaps their studies have shown indoor humidty drive at 100% this will never happen. Think I wall call them today. Air barriers (completely different than vapor, or some such as plastics can do both) they say can be anywhere, air transports heat/cold through the walls making up a critical part of breathable walls to exchange air in small amounts/hour...more on thermal mass soon

I was doing some research on Durisol yesterday since they said they “mineralize” their wood chips and bond with 20-30% portland cement. When I goggle mineralized wood petrified wood comes up that seems to last forever. http://creationwiki.org/Petrified_wood

Here are some quotes:

“Wood decomposes extremely fast in environments where trees typically grow. This happens because wood is composed of sugar (cellulose), which is the preferred food for microorganisms such as bacteria and fungi. Even modern pressure-treated woods can not escape decomposition.”

“The speed at which decomposition takes place is determined by the temperature, moisture, availability of oxygen, and the type of wood. Under normal forest growth conditions, most trees decompose completely in only a few decades. Even the species of trees that are slowest to decompose, such as the western red cedar, will disappear completely in under 150 years “

"Uniformitarian geologists frequently tout that fossilization requires millions of years, but there are many modern examples where organisms or artifacts have become fossilized rapidly. Wood can become quickly mineralized if buried or submerged in a highly concentrated salt solution where carbonates are precipitating. There is even a U.S. patent whereby wood can be treated with a silicate solution rendering the characteristics of petrified wood. US Patent for Petrified Wood Patent No. 4,612,050: “A mineralized sodium silicate solution for the application to wood has a composition causing it to penetrate the wood and jell within the wood so as to give the wood the non-burning characteristics of petrified wood.” [2]. Researchers at the Pacific Northwest National Laboratory found a method to create petrified wood in just a few days. "

So perhaps we preserve our wood with a spray application of mineralized sodium silicate?

I've done a short book summary/'where to get it' of this book HERE
Please add any more videos, etc. to that thread that seem appropriate or pass them on to me and I can add them .
....and we need some reviews with ACORNS

Terry Ruth wrote:Bill, yes very interesting informative book and you know what just baffles me is I have been told that "no measurable data exist" and these methods are controversial. There is all kinds of data that results from measurements above. So the next time someone claims that we can point them to this thread

Definitely, as this data and interpretations of are quite hard to find; it seems purposely obscured!

Terry Ruth wrote:
The clay data seems consistent, lime varies with surface finish. 1:2, 1:3, them pumice/lime sounds great as insulating and water proofing with high perm. If the surface is burnished to close structure more of a water barrier is created if that what one wants, with the smaller the pore size. What mix of lime and pumice and what type lime are you using?

I am using 1:1 type s hydrated lime to local pumice/ash mix.

Terry Ruth wrote:
Where do I get pumice? Scoria" or other insulating rock that drains well? I know I can get perlite at Walmart in spring but it's a little expensive around here and large quantities, small bags to a job site does not seem very appealing.

Well, I just picked up my first 2000 lb superbag from the Limestrong plant. They are a new start-up that produces an exact replica of Roman concrete(pozzolanic lime this is the Holy Grail to me). Little bags are 1000 lb and sell for $350. They have asked me to distribute, so send me a pm if you want a bag. This pumice is within 1-2% in all chemical analyses of Vesuvius, where the Roman builders got their pumice/ash.

Terry Ruth wrote:
Dursiol, has me a little confused. They have a very open pore, permeable, ICF form with excellent properties it appears but they support an exterior petro barrier and have no test results on the burnishing of lime you mentioned with their product, or other test results of natural barriers. From what I can tell at this time anyway by the data, that closed pore surface finish will produce a barrier and allow high permeability we want under slabs, exterior walls...or option 3 or 4 above. Durisol suggest a "parge coat" of portland cement/sand to close pores for stucco's on their product, cladding with vent gaps behind it. I need to call again and talk to an Engineer not sales....the book has more on Durisol later, which, if you wanted to take the manufactured product route for fast ease of construction looks to be one of the better ones. Far better than most SIPs. Don't let the lower r-value fool you, another myth discussed soon. What I figure is as George said (full breathable walls is not always desired) in some cases such as Durisol where the material has a high ability to store vapor on the interior side and prevent diffusion it to the concrete or to exterior barrier that does not have an ability to absorb or dry fast, then get trapped by an exterior barrier I question. My concern is if the warm humid inner wall saturates to the exterior barrier that does not allow drying to the outside if it is dry, purhaps their studies have shown indoor humidty drive at 100% this will never happen. Think I wall call them today. Air barriers (completely different than vapor, or some such as plastics can do both) they say can be anywhere, air transports heat/cold through the walls making up a critical part of breathable walls to exchange air in small amounts/hour...more on thermal mass soon

I like the product, but I don't want a OPC foundation in any form.
I agree with George that you don't want a fully breathable wall system. What we want is a wall that is breathable as possible on the inside and has resistance to breathability on the outer skin. I think the trditional 3 coat lime plaster inside and out, with a highly breathable interior like adobe or cob is the ultimate wall assembly. I say that after living in one for over 20 years.

Bill, thanks as soon as I get closer to a build I’ll be in touch. I use hydrated S too, I’d probably go with SA under a slab, but I’d have to order it.
Here are some good sources for lime types and applications: Our hydrated types in the USA are similar to hydraulic in Europe or NHL 2, 3.5, 5, the lower have less cement/strength or MGO like high calcium we use.

http://lime.org/about-us/faqs/

http://www.masonrysystems.org/pdf/Choosing-the-Right-Mortar-for-the-Job.pdf

Here is a convenient property table: Care has to be taken since what is best in one climate or time of year may not be in another, or mortar may differ than plaster/stucco depending on desired properties.

Thermal Mass: A confusing topic in how if differs from walls that are highly insulated, and how they both differ in their ability to manage moisture and dry.
Defined by the USA National Bureau of Standards as: “The mass effect relates to the phenomenon in which heat transfer through walls of a building is delayed by the high heat (retention) capacity of the wall mass….also referred to as “thermal capacitance” or time lag – the resistance of the material….over time to allow change in temperature to from one side to the other”

Mass walls that are known by low R-values are deceptive. Conventional wood framed walls of higher R-values on average only hold on to heat/cold for 10 mins. Mass walls radiate for up to 12 hours. The effects of on site lite wood stud thermal bridging alone can take an R-value of 20 down to a whole R-value of 13, and moisture diffusion that knock down R-values are not accounted for in-situ, breathable massive walls are not affect by.

The phenomenon: As cold winter air eventually migrates its way to the inside of any of these breathable, thick walls, 70-90% of the temperature gradient between the outside air and indoor air disappears by the time the air reaches the inner surface, up to 10-12 hours later. This happens because the inner one third of the walls that is roughly the same as the indoor air. As outdoor air slowly diffuses through this last (inner) one third of the wall, it gradually warms as it moves through. Therefore at least several hundredths of a room air exchanged per hour is possible on the passive basis without significant thermal loss, provided you also use what is consider to be “breathable” interior and exterior finishes.
The key is the slowness of the migration of air and the fact that it mixes with pockets towards the inner part of the wall containing warmer air in the winter and cooler in the summer. Compare this to faster cold air infiltration (not slow diffusion) entering a wood frame wall from outside in all the ways builders have come to loath: between adjacent studs, around windows and electrical outlets, or between insulation in a cavity, penetrations, etc.

NOW YOU CAN SEE WHY A BREATHABLE, THICK WALL, WITH ITS ABILITY TO DRY OUT AND TO SLIGHTLY REFRESH AND EXHANGE INDOOR AIR WITH OUTDOORS IS NOT A HINDERANCE TO SUPERIOR THERMAL PERFORMANCE.

A “flywheel effect” is created by the combination of temperature modulation and thermal lag in thick wall construction. The wall temperature will defer hour to hour as the conditions within the inner one third of the wall shift in response to the hourly change in temperature in either side of the wall. This provides a self-regulating mechanism. For example, the book refers to proven examples, and there are many others I have seen, that the outside wall is reversing direction taking on temperature when outdoor heat is high, releasing when it when low, that has not effecting indoor air temperatures. Even if the diurnal temperature swings are not large enough to cause a reversal of direction, there is always a delay. This delay often saves money in the case of cooling loads when electric cost may be lower. Smaller AC cost offsets higher building cost, if any.

Here is another study Clemson University did that shows the surface of brick acting independently with no thermal bridging to the interior from a hot 100+F exterior days. Scroll down to the video and “Thermal Mass” section: http://hopeforarchitecture.com/blog/

Under conditions of predominantly cooling, this heat flow reversal results in a substantially smaller heat gain by the overall structure because some of the heat initially absorbed by the outside wall surface NEVER reaches the inside surface (see graph). Rather this portion of the heat is released back to the outside later in the day or at night and that much less air conditioning is needed. Moisture regulation of indoor air also reduces cooling loads. Natural ventilation may now be all that is need, vs mechanical devices like ERV/HRV’s (heat and moisture recovery units). In climates where cooling loads and peak usage are high like commercial buildings, the shift can reduce cost.

Experimentally quantifying the thermal mass effect in the field is hampered by the practical difficulties of matching all building materials by R-value and identifying environmental operating protocols in wood-frame and massive construction. R-value can be very misleading.

Lots of other benefits to mass, power outages, cold-hot spots, etc, noted. The book also discusses another method of “outsulation” by placing insulation behind an interior mass material like clay, lime, or wood, so it isolates the interior from the exterior for thinner walls, and the inner walls become a “whole building” system. Foam, as in ICF interior would not allow the mass to have beneficial effects as noted above. Insulation as a center core with mass like concrete would be a good example, Orlando National Labs has conducted test on it compared to conventional studded walls and assigned a benefit (Dynamic Mass Benefit Value) to mass walls in an attempt to quantify it you can find on their site They also have an on-line calculator that compares for ten USA climate zones.

More on Radiant Heat Transfer next.

I wont go into all the human biology or anatomy the book goes into to proof this conclusion but how many agree that radiant heat is more comfortable than hot forced air that needs to cycle more often due to high insulation and low mass designs? I find the later very uncomfortable especially with hot and cold spots throughout the home. How many when they do their HVAC loads calculations take into account human factors that drop or increase the load? The second statement below I find absolutely true. The way the sun heats on a cold day with fresh air outside would be a good example of this.

So, does this really matter?

I believe breathability and the control thereof is the single biggest improvement that you can make to a home!

This is how important it is to me.

Terry Ruth wrote:Here are some good sources for lime types and applications: Our hydrated types in the USA are similar to hydraulic in Europe or NHL 2, 3.5, 5, the lower have less cement/strength or MGO like high calcium we use.

I am in Europe and could not understand why I could always read "lime" without precision!
I have hydraulic NHL 3.5

Are you interrested that I post pics of wall/ceiling that was wetted and dried a few times?
I am quite interrogative with the resulting "designs" from white to grey!
I begin to understand that the white might come frm the carbonation process... Right?
What is under the lime plaster is different from place to place, from cement to bricks, and stone.

I arrive to this post because I need to stop this water leeking through the cliff, 10m above.

Bill, nice job, you got that right, but how do you convince clients?

Xisca, I put a response on your thread, do not worry about color, look at the MGO and Calcium pure contents by percentages, or the guide lines and usage the manufacture suggest. We in the US classify our lime differently that is the only difference, and some market battles between us that have to do with purity and quality. The ones you have to watch out for are AHL, or ALs, "Artificial" that have other ingredients like portland cement, slag, pozzolans, gypsum fillers from power plant kilns, to cut cost that are less natural sometimes referred to as industrialized junk lime. Do not buy anything that is listed as "proprietary blend" it could have junk fillers in it.

Here is the process: Kinda interesting, http://lime.org/lime-basics/how-lime-is-made/

Your best shot at sealing a limestone rock is start with NHL 5, add portland cement until it seals.