WOFATI with cob instead of plastic?

In this post and the couple around it, the idea of replacing the plastic used to keep the water out of the wofati with natural plaster was introduced. I think this might be a good idea and would like to discuss it further.

By replacing the first layer of plastic that wraps the wooden structure with natural plaster, a couple things happen.

First the draft that comes from between the logs exposed to the outside would be eliminated. Paul mentions it here, but in his drawing only the cracks between logs are filled and then the plastic is still wrapping the structure. I am suggesting plastering not just between the cracks, but over all the wood on the exterior where the dirt will be filled in. This should repel any moisture which happens to make it down to this layer right?

Secondly I think using the cob method would allow for better moisture/humidity control in the building. Reading this thread on breathable walls is very informative. It seems that if you have plastic directly against the logs with dirt on the other side, there could be a moisture problem with the humidity coming from the inside of the building and not being able to escape due to the plastic barrier. With the natural plaster approach, it seems as if this trapping of moisture against the barrier is solved. Thoughts on this?

Now what if we went and replaced the second layer of plastic that acts as the umbrella with a natural plaster as well? This should allow for the building to breathe even better right? Here Bill mentions a natural plaster/stone shingle idea with a layer of gravel/stone, covered in filter cloth, between the plaster and rest of the back fill. I guess the gravel layer would allow the water which makes it through the top layer of dirt to flow easily down the plaster umbrella to the ground. If there was no gravel layer between plaster and dirt would the plaster just turn back into mush clay with over saturation? Would this happen even with the gravel layer?

I understand this would be considerably more work than just using plastic, but it would also be way less imported material. It might also be longer lasting. What do you guys think? Would this work or not?

That is a very interesting idea, here's what i think:

Replacing the bottom layer of plastic with plaster will result in inner moisture going into the roof and getting trapped there by the upper layer.

Plaster as the umbrella layer will deteriorate sooner rather than later i suspect due to water damage it will go in at a much higher rate than it'll have a chance to dry.

I wonder if in the green roof situation, if the roots are gonna become a problem for the umbrella plaster even if the water damage problem can be solved.

A lot depends on how moist your climate and soil are.

Our buildings here are buried in the earth on the north side, and we didn't use any plastic. Just a stone wall, backfilled with the tighter of the various soils available within arm's reach, and then natural plaster on the interior wall. BUTTTT our climate is totally arid, there is no precipitation to speak of (at least not every year, and the rare events soak in only a couple of inches at most), and the soil is bone dry except where irrigated or along stream sides.

That's a big BUT. What's the soil moisture like in your environment?

And if you are never going to heat the Wofati so it stays cool, not much warmer than the soil, there might not be much condensation. But if you're going to add heat and moisture in there (burning wood or anything, humans breathing, cooking...) then there will be a difference in the relative humidity of the air in the living space and the soil, which may lead to condensation.

Voy Grabiec wrote:
Replacing the bottom layer of plastic with plaster will result in inner moisture going into the roof and getting trapped there by the upper layer.

It seems like it might eh? The insulating layer between might get all wet then. Hard to say. I suppose it also depends on the amount of moisture/humidity being generated and trapped in the building with no place to go but out through the plaster.

Voy Grabiec wrote:
Plaster as the umbrella layer will deteriorate sooner rather than later i suspect due to water damage it will go in at a much higher rate than it'll have a chance to dry.

This also seems like a very real problem. I think this is where the idea of the stones as shingles plastered in and then the layer of gravel to help the water run out comes into play. But... I'm not even sure that is possible.

Voy Grabiec wrote:
I wonder if in the green roof situation, if the roots are gonna become a problem for the umbrella plaster even if the water damage problem can be solved.

Maybe, but I guess you would want to stick with plants that have shallow root systems. I'm not sure they would puncture the poly even if they did get down there though. In the case of the plaster instead of poly, there might be a bigger problem if the plaster starts turning back to clay.

Rebecca Norman wrote:A lot depends on how moist your climate and soil are.

Our buildings here are buried in the earth on the north side, and we didn't use any plastic. Just a stone wall, backfilled with the tighter of the various soils available within arm's reach, and then natural plaster on the interior wall. BUTTTT our climate is totally arid, there is no precipitation to speak of (at least not every year, and the rare events soak in only a couple of inches at most), and the soil is bone dry except where irrigated or along stream sides.

That's a big BUT. What's the soil moisture like in your environment?

That's dry! Where I am receives 30 - 35 inches of rain per year. Quite wet.

Rebecca Norman wrote:
And if you are never going to heat the Wofati so it stays cool, not much warmer than the soil, there might not be much condensation. But if you're going to add heat and moisture in there (burning wood or anything, humans breathing, cooking...) then there will be a difference in the relative humidity of the air in the living space and the soil, which may lead to condensation.

I would also want to heat it, as I don't think it can go without a heat source all winter long. RMH for sure.

It all does really depend on the climate and levels of moisture/humidity I suppose. The plaster idea might work very well in your climate with such little moisture.

Simon Johnson wrote:
It seems like it might eh? The insulating layer between might get all wet then. Hard to say. I suppose it also depends on the amount of moisture/humidity being generated and trapped in the building with no place to go but out through the plaster.

The molecular weight of water (H2O) is significantly smaller than that of the air. Water vapors (or humid air) have the tendency to go up because of that. The ceiling would be first to suffer i think.

Simon Johnson wrote:
This also seems like a very real problem. I think this is where the idea of the stones as shingles plastered in and then the layer of gravel to help the water run out comes into play. But... I'm not even sure that is possible.

It may work with enough shingle layers, overlap and pitch. Not all the rain water would actually get through the top dirt/plant layer i imagine. The challenge would be designing the shingle/ gravel layers so water could drain where it wouldn't hurt the structure.

Simon Johnson wrote:


Maybe, but I guess you would want to stick with plants that have shallow root systems. I'm not sure they would puncture the poly even if they did get down there though. In the case of the plaster instead of poly, there might be a bigger problem if the plaster starts turning back to clay.

Given enough time roots will find their way anywhere and go through anything i believe but even if they never reach the plaster there may be another issue worth looking at: The roots could eventually get into the gravel layer, rot, deteriorate and turn into soil which could clog the gravel layer.

Could that be managed by creating a thick enough top dirt layer with shallow root plants or would a root stopping layer on top of the gravel be necessary? Could that be another layer of stone shingles on top of the gravel layer?

So maybe there is a certain annual precipitation, or relative humidity, level over which the natural plaster method would not work out and the poly method would work out better, but the natural plaster method could work out very nicely in climates with a low annual rainfall?

In a climate with a high annual rainfall, might it be better to use a more heavy duty plastic material, like the pond liner stuff? Less chance of making a hole in it and should stand the test of time better in general. Should also be better able to keep water out when/if the top 2' layer of dirt/soil becomes saturated in spring time.

In terms of the moisture that accumulates from the inside of the building from activities like cooking and bathing, maybe those living in the wetter climates need to be diligent about keeping that humidity level in the house down. I would think that burning a rocket mass heater or wood stove would help to keep the humidity down, both with the heat being generated and the sucking in of fresh air by the stove. So maybe burning wood when necessary and opening/closing the windows when appropriate is going to be key to avoiding problems?

It seems that in the temperate climate with high annual rainfall, you have two moisture problems to deal with, the one coming from the sky to soak in through the earthen roof, and the one coming from the humidity generated from the inside of the building. How to stay dry from both?

Another dilemma i see is always moist (green) and sometimes wet/saturated roof vs dry celling.

One of the solutions that comes to mind would be a vented attic. I'm not sure if that would be a WOFATI anymore. But it could work .

Another one could be a system of ducks just below the stone shingles through which exhausts from the rocket stove could run and keep the moisture away fro the plaster.



Those are just brainstorming idea but i am interested in the green roof without plastic idea and i'd like to hear other opinions.

Maybe we can clear up a couple of common misconceptions here;
1) water vapor does not rise, warm air rises and carries more water vapor than the colder air that could be stratified below it, giving that illusion
2) Lime/clay plaster will not degrade from wetting - water is actually the medium that builds up the carbonation/lithification process
3) in order for vapor to condense, there must be a condensing plane at 100% RH - plastic is perfect for this
4) vapor drives through a structure in the direction of warmer to cooler, eventually finding equilibrium unless #3 happens, then water accumulates on the surface of the condensing plane.

I was out walking the other day and took these pictures of soil spontaneously carbonating, creating a truly natural plaster layer. This was created on the side of a stream where repeated wettings have started the lithification process. If you can get a bit more control than this, I don't see why your natural roof wouldn't get stronger with age!

Bill Bradbury wrote:Maybe we can clear up a couple of common misconceptions here;
1) water vapor does not rise, warm air rises and carries more water vapor than the colder air that could be stratified below it, giving that illusion
2) Lime/clay plaster will not degrade from wetting - water is actually the medium that builds up the carbonation/lithification process
3) in order for vapor to condense, there must be a condensing plane at 100% RH - plastic is perfect for this
4) vapor drives through a structure in the direction of warmer to cooler, eventually finding equilibrium unless #3 happens, then water accumulates on the surface of the condensing plane.

I was out walking the other day and took these pictures of soil spontaneously carbonating, creating a truly natural plaster layer.

Good points with the exception of 1)

Water vapors (gas) are just invisible as air. Moist air is lighter than dry air of the same temperature. What you were referring to in your comment is water mist (tiny droplets of liquid water) rather then vapors and yes mist is heavier than air and won't rise on its own. When water vapors meet colder air some of it condense and create mist. They also condense when they meat colder objects (like a celling for example).

Now the answer to the question if that makes celling more vulnerable to inner moisture than walls and floors may just as well be no but i wanted to clarify what i meant.

I pressed my wet fingers on a breathable plaster wall in order to show how water will not enter into a medium that is warmer than it is, be it the soil or a wall. The warm fingerprints have driven the moisture to the outer edges where it was absorbed by the cooler wall. The fourth finger was not wet, so it doesn't have the dark ring.
The next image is of my adobe wall, showing temperature differential across the mass.
Tomorrow I will photograph and post here an old ruin that has no roof, yet the lime plaster is still doing great.

Bill Bradbury wrote:I pressed my wet fingers on a breathable plaster wall in order to show how water will not enter into a medium that is warmer than it is, be it the soil or a wall. The warm fingerprints have driven the moisture to the outer edges where it was absorbed by the cooler wall. The fourth finger was not wet, so it doesn't have the dark ring.
The next image is of my adobe wall, showing temperature differential across the mass.
Tomorrow I will photograph and post here an old ruin that has no roof, yet the lime plaster is still doing great.

That is way cool

When you say lime plaster do you mean lime+sand+water or something else?

Voy Grabiec wrote:

Bill Bradbury wrote:Maybe we can clear up a couple of common misconceptions here;
1) water vapor does not rise, warm air rises and carries more water vapor than the colder air that could be stratified below it, giving that illusion
2) Lime/clay plaster will not degrade from wetting - water is actually the medium that builds up the carbonation/lithification process
3) in order for vapor to condense, there must be a condensing plane at 100% RH - plastic is perfect for this
4) vapor drives through a structure in the direction of warmer to cooler, eventually finding equilibrium unless #3 happens, then water accumulates on the surface of the condensing plane.

I was out walking the other day and took these pictures of soil spontaneously carbonating, creating a truly natural plaster layer.

Good points with the exception of 1)

Water vapors (gas) are just invisible as air. Moist air is lighter than dry air of the same temperature. What you were referring to in your comment is water mist (tiny droplets of liquid water) rather then vapors and yes mist is heavier than air and won't rise on its own. When water vapors meet colder air some of it condense and create mist. They also condense when they meat colder objects (like a celling for example).

Now the answer to the question if that makes celling more vulnerable to inner moisture than walls and floors may just as well be no but i wanted to clarify what i meant.

Sorry Voy,
you are completely correct there, it is condensing mist that falls and steam rises, but water vapor is typically entrained in the air, so inside a home it moves with the air unless you have a steaming kettle or some other major steam producer. The air, unless disturbed, stratifies according to density(temperature), with the highest temps at the ceiling along with the most water vapor(because warmer air carries significantly more water vapor) and therefor the highest possible vapor adsorption.

This is not a problem unless the ceiling plane is cool, then the ceiling could condense water from the air and begin to absorb the bulk moisture, warming the ceiling with latent heat as it does. As long as the ceiling is of a breathable material and there is not additional cooling from drafts or lack of insulation, as the ceiling warms, condensation will stop and the absorbed water will return to the air when interior humidity goes back down.

Voy Grabiec wrote:

Bill Bradbury wrote:I pressed my wet fingers on a breathable plaster wall in order to show how water will not enter into a medium that is warmer than it is, be it the soil or a wall. The warm fingerprints have driven the moisture to the outer edges where it was absorbed by the cooler wall. The fourth finger was not wet, so it doesn't have the dark ring.
The next image is of my adobe wall, showing temperature differential across the mass.
Tomorrow I will photograph and post here an old ruin that has no roof, yet the lime plaster is still doing great.

That is way cool

When you say lime plaster do you mean lime+sand+water or something else?

Thanks, yes lime sand water and usually horse hair and dung. Mix in 40-50% clay and set the stones like a neolithic man.

What I am struggling to show is how moisture in the wall assembly drives outward most of the time in a cold climate, actually drying the soil. So there should be no problems unless soil temps go above interior temps which may happen for a short period in summer, but rainfall and infiltration would be insignificant then.

This photo is of saturated soil next to a concrete basement wall, north side. You can see the soil is dry next to the wall because the heat lost from the basement is driving moisture away.

Great stuff here guys.

So Bill are you proposing that even in wet climates the natural plaster should still work to repel the water from above, while allowing the inside of the building to dry out? So long as the inside temperature of the building stays above that out the outside?

I guess in the summer the temperature would be warmer outside than inside, but the amount of precipitation should be relatively low and be handled simply by the top layer of dirt/soil. In the winter the top soil/dirt layer should stay pretty frozen and covered in snow (where I am anyway), so the amount of moisture coming down shouldn't be a problem then either.

The tricky time I think, is spring and fall when heavy rains come and snow is melting. I suppose these periods of time aren't too long and if there was some moisture build up it could dry out during the summer or winter months? I expect the RMH would be running most days during fall, winter, and spring as well.

"As long as the inside of the building stayed warmer than the soil"
So it would be okay as long as someone was living there but what if the building was left unheated (while building - if it took more than one year to move in)
During winter...is an empty building warmer or colder than the earth?

Simon Johnson wrote:
So Bill are you proposing that even in wet climates the natural plaster should still work to repel the water from above, while allowing the inside of the building to dry out? So long as the inside temperature of the building stays above that out the outside?

Yes, I believe so, but I think you would want to significantly increase the amount of lime and maybe use a seaweed glue or some other plasticiser, which would increase price.

Simon Johnson wrote:
The tricky time I think, is spring and fall when heavy rains come and snow is melting. I suppose these periods of time aren't too long and if there was some moisture build up it could dry out during the summer or winter months? I expect the RMH would be running most days during fall, winter, and spring as well.

I think this can be done with only small amounts of wood being burned, but there needs to be times of large solar gain to the mass, which would then be stored. I like the idea of underground tubes running from a greenhouse to the south and exiting to the north of the home and I think the wings could be plastered with lime to a mirror polish and positioned for maximum reflectance on the interior mass.

With solar gain, I think this design could be quite effective.

Meagan Poisson wrote:"As long as the inside of the building stayed warmer than the soil"
So it would be okay as long as someone was living there but what if the building was left unheated (while building - if it took more than one year to move in)

If a building gets cold, it can get quite damp.

Meagan Poisson wrote:During winter...is an empty building warmer or colder than the earth?

If we are to build in harmony with the land, then we must design our buildings to heat and cool themselves as much as possible. Most buildings, including the one I live in would get considerably colder than the earth they are in/on if they did not receive copious amounts of heat input.
This is a noble pursuit, going without heat, but a very lofty ideal; achievable only through meticulous design and detail. Good luck, it looks like you have a great start!

Hi, Simon asked I chime in and give some thoughts. He provided a link to the thread I created on "Breathable Walls" . I read the first two post and Simon is correct you do not need plastic it chokes the wall. Clay renders, and/or straw, lime, provide the best performing vapor, water, air, heat/cold, regulating system and ability to store, find equilibrium moisture content (EMC) to the interior wall based mainly on Relativity Humidity. Mold is said to be created above 70% RH within a 48 hour window, and once it hits that threshold there is no turning back. My latest post talks about a holistic approach to preventing this.

The data I posted provides concrete evidence as in world class modeling, field data, put together by teams of top scientist throughout the world. There is no need to speculate and/or debate. It shows hygroscopicity of many natural and modern building materials, drying speeds, compares them, defines the pitfalls of plastic barriers and other modern materials like drywall clearly. The data is a little difficult to understand so I am trying to simplify it, and imagine some of the reports state that they are simplified for the laymen to understand. In other words, this is a very complex science we see people trying to make sense of over and over, so I thought it be best to look at the data closely and try and straighten out the myths in the natural building world. Not entirely to my surprise there is a whole lot more to it than perm rating and drying directions most use to make design decisions. It is material technology and processes related to building's we are looking at. With that knowledge one should be able to mate materials more effectively.

I invite all to point to this thread when in doubt and look at the data, ask questions, discuss it. We looked at some application, strawbale, clay-slip, clay/lime renders Bill posted, now Dursiol ICF's. Rather than rewrite the thread here please bring any questions or applicable discussions to it. Next I'm going to finish up with Durisol (If you did not read the last two post, it got real interesting) with some field testing, then Capillary adsorption/absorption where things get a little hazy. Later, we get in MGO I am looking forward to that

Here is the link to Terry's thread on Breathable Walls.

So, I'm always going on to my apprentices about lime carbonation from repeated wetting and drying. While scraping the paint off along with the latex impregnated lime veneer down to the gypsum over lime plaster, they came to a place where the lime veneer simply would not budge. They called me in to say "now we get it", so I took a picture and here it is.

You are looking at the ceiling of a bathroom that has had an extraordinary amount of water leaking in on it from the roof. The plaster has cracked and lost it's key because of the different rates of expansion when the 2 materials(wood and plaster) swell and shrink again from wetting. So some of the plaster was taken down, but what remained was nearly impervious to a carbide scraper.

so i've read a good portion of these 2 threads, but not all.

Has the idea of adding rocks as a drainage system over a shake/shingle roof been an option put out there? of course it would introduce a lot of load, but perhaps some sort of drainage system is the right direction. perhaps it would not have the same insulative properties, but perhaps it would.

What sort of lime are you talking about?
There are many limes,
mainly I have heard about aerial (very white and not very strong)
or hydraulic (nearly as strong as cement for building, less white).....

I heard that hydraulic lime should never be mixed with clay.
(something like "because what the clay does is already in there".

About cob, the only problem I can see is that it cracks when it is not all the time wet.
So this would be great for an all-the-time-wet-pond.

It's difficult to get around plastic on a roof, especially low pitched or flat live ones that collect water.

Xisca, I put this on your thread: https://permies.com/t/44629/natural-building/waterproof-green-roof-planting-top

One way is to create a gap (3/8 or larger) between the roof cladding (soil, slate, shake) using MGO boards (2). The lower one sits above insulation, the upper below your roof cladding as sheathing. You insulate below the lower and this could be sealed (for very cold climates) or open vaulted or attic. In cold climates, a raised heel truss or "energy heel" stuffed with insulation (cotton dries fast, or inert mineral wool drains and dries fast to the vent/outwards). T&G ceiling. No tapes or caulks on any joints provides a fully breathable assemble, the parge coat provides an air seal too. MGO absorbs and dries much faster than wood sheathing, inert, non magnetic or thermally conductive, needs no barrier.

A parge coat of MGO/lime/clay (kaolin preferred) acts as a capillary break applied to the vent/rain planes, or lime burnished by wood or steel trowel (NHL 3.5 ) on the lower upper surface, NHL type 5 common to your soil burnished since it's denser and rated for water. Two layers of a highly absorbent /desorbent MGO board with all natural surface treatments parge coats for vapor, a gap for water drainage and ventilation, and inner layer of clay or lime plaster or wood provides triple layer water and vapor management/protection. Run some water proof small sample ground test first with the parge coats to get the mix right, especially the one with the NHL 5, but even if it fails it drains to a ventilation/drainage gap that air vents between the soffit or open overhang and ridge vent, or attic vents, or turbine cans. If you can use well drained soils/plants or per-lite/vermiculite that would help capillary wicking to the insulation or roof leaks due to gravity and pressures, and reduce mold growth. May not need rain and ice on the edges but may not hurt the lower 6 inches if it freezes there, if you can find a non-toxic high perm rated one.

A substitute for MGO board would be low density fiber-cement board if you can find a company like Durisol or Faswall over here. They use portland cement and clay or ceramic mineralize recycled soft woods that neutralize or petrify the wood so it bonds better to cement, like wood chips and clay, but in a sheathing board. OPC provides an alkaline or high PH (above 7) surface to prevent mold.

"I have learned that hydraulic lime is not good to mix with clay!
I do have access to clay, but a very difficult land (steep, difficult access)
They say that aerial lime is fine with clay. (dunno the reason)"

This is not true, the difference between the two is one has more air than the other, that is all. NHL's contain clay from manufacturing limestone which naturally contains some clay. We have been using AG lime (high calcium, little MGO) with soils for a long time and still do, Fly ash too which is considered a pozzolan or geopolymer, has calcium and other ingredients depending on grade. It also has heavy metals (very small traces) some do not like. Do not worry about the color, each manufacture has a different burn process....look at the content and usage guides the manufacture offers on the label/MSDS/SPEC sheets or call them. We use primarily type S (your 3.5) in the US, or N (your NHL 2), NHL 5 gets close to our portland cement we mix with S or N, or SA / NA, A=Air Entrained or additive, if we want more air insulation, same is done with your NHLs.

Hope that helps.

Lime is a much misunderstood product, so a little vocabulary;

Limestone- Often the criteria associated with these products are the particle size and the purity of the limestone.
Limestone is also known as: Limestone Road base, Ag-lime, Crushed limestone, Calcium Carbonate, CaCO3

Quicklime- Often the criteria associated with this product is the chemical purity, the quicklime reactivity and the particle size
Quicklime is also known as: Burnt lime, Active lime, Calcium Oxide, CaO

Hydrated Lime (Powder) - Often the criteria associated with these products are the particle size and the purity of the hydrated lime. The purity can be expressed as a percentage of its Calcium Hydroxide component or by its Calcium Oxide (Quicklime) component.
Hydrated Lime Powder is also known as: Lime, Powdered lime, Hylime, Builders lime, Slaked Lime (See below), Calcium Hydroxide and Ca(OH)2

Hydrated Lime (Liquid) - Often the criteria associated with these products are the solid content in the liquid or its chemical equivalent expressed as a percentage of its Calcium Hydroxide component or by its Calcium Oxide (Quicklime) component.
Hydrated Lime Liquid is also known as: Lime Putty, Lime Slurry, Milk of Lime, MOL, Calcium Hydroxide slurry, Calcium Hydroxide, Hydrated Lime slurry, Slaked lime and Liquid Lime.

Some basic questions for greater understanding of different lime products could be poised as this......

Q: What is Calcination?

A: CALCINATION - Calcination is where limestone or limesand is burnt in a kiln. The raw material temperature is elevated to beyond 825C causing it to decompose. The resultant of the thermal decomposition is Quicklime with Carbon Dioxide released as a by-product.

CaCO3 + Heat ↔CaO + CO2
100g 56g 44g

Q: What is Hydrated Lime?

A: HYDRATED LIME – Is a derivative of Quicklime, the result of the hydration reaction between Quicklime and Water. The reaction also generates heat. The amount of water added will determine the whether the hydrated lime is a powder or a liquid. Hydrated Lime is available as a powder or a liquid.

CaO + H20 = Ca(OH)2 + heat

Q: What is the difference between Slaked Lime and Hydrated Lime?
A: Slaked lime and hydrated lime are often confused. Technically the addition of water to form a hydrated lime in powder form is called hydration. When the addition of water produces hydrated lime in a liquid form this process is called slaking.

Q: Is Agricultural Lime the same as Lime?

A: The term agricultural lime, or "Ag-lime," usually refers to limestone. Limestone (calcium carbonate) is not the same as hydrated lime (calcium hydroxide).

NHL refers to naturally hydraulic lime, this is a lime with clay impurities that act as a natural pozzolan.
Hydraulic lime is a hydrated lime with added pozzolan that will set under water through a secondary reaction that doesn't require air like the primary reaction in lime(carbonation).

Interesting Bill. Back when I was trying to sort out the difference between NHL and Hydrated I had heard the NHLs were more pure from a European Supplier, then I talked to a Chemist at Carmeuse in the US that said we make more pure lime. This is getting above my head but it appears the NHLs use pozzolans to get their cement strengths from low to high NHL 2, 3.5, 5....same as hydrates use MGO to get it's, Type N (low MGO) or "High Calcium Lime or Pure Cal (Calcium over 86%)" , TYPE S (higher MGO and stronger). The AG limes we want to stay away from for buildings. I could be wrong but it also appears the NHLs due to impurities won't absorb as much CO2 due to the second pozzolan reaction. It is my understanding the Calcium content is mainly responsible for CO absorption/desorption. Again getting above my head and perhaps more than I need to know

I purchased a couple bags of a "proprietary blend" hemp binder imported from Europe back when I didn't know better. Soon after I blended some different mixes of N, S, with using fly ash as a pozzolan I got from my local coal firing plant as waste real cheap. Make a great roof and wall insulation, you can poor water in it and it sucks it up like a sponge and evaporates it fast, does not freeze, if you add more MGO or fly ash it gets stronger you can see the middle brown one held together better, less insulating. See attached, I tested different mixes. I ended cutting cost and embodied energy of my hempcrete by over 70% and that will better when CO starts producing more hurd. The same can be done with straw in the meantime. Type N left then Type S...I pulled my forms in an hour and it was hot and humid out to see how fast I could build without break outs. I changed the stud depth too which makes a difference in break outs. More cement dried faster so I could render faster....some were having to wait 3 months using NHL 3.5 that was not going to work for me. Now some are coming out with hemp binders with fast drying times >20% MC, like 1-2 days they claim, getting ready for the US hemp market boom.

The folowing is straight from the LimeStrong website; I've been blow away by this product, so I don't mind plugging for them a bit.

For as long as ordinary lime plaster and mortars have been around, people have been amping performance and strength with reactive additives, or pozzolans (an effect known as gauging). A pozzolan is defined as a material that is capable of reacting directly with lime in the presence of water at ordinary temperatures to produce cementitious compounds. One of the most effective of these (as the Romans discovered and modern research done by the University of Utah and others confirms) is a pozzolan made from volcanic pumice. LimeStrong, then, by deliberately pairing lime with a reactive pumice pozzolan, is a Artificial Hydraulic Lime (AHL) product.

The reactive quality of the ingredients, the wisdom behind the mix design, and the consistency in production make LimeStrong a dependable and predictable lime-pozzolan product.

The lime-plaster marketplace also features Natural Hydraulic Lime (NHL) products that are mined from very specific lime deposits (typically European) that inherently/naturally contain the necessary hydraulic properties needed, although the costs of NHL products put them out of reach for many.

NOTE: hydrated lime is not the same as hydraulic lime. Hydrated lime cures only via recarbonation.

LIMESTRONG IS NOT A CEMENT-LIME PRODUCT. The workability and durability characteristics inherent in hydrated (slaked) lime plaster and mortar are so desirable that lime is commonly added to standard cement-and-sand plaster and mortar product formulations to amplify ease-of-use and increase performance. Unlike these tweaked-up cement-lime products, LimeStrong products eschew the use of brittle-setting Portland cement and heavy sand altogether. LimeStrong is formulated with lightweight pumice aggregate and fine pumice pozzolan, realizing every performance and usability gain while completely avoiding the cement-sand problems.



TECHNICAL DATA. Chemically, slaked (hydrated) lime and fine-grained pumice perform together beautifully. The impressive durability of cured LimeStrong plaster happens on two levels.

THE FIRST: Hydrated lime, when mixed with water, will return to its limestone (CaCO3) origin as it dries, acquiring carbon dioxide from the atmosphere that “carbonates” and hardens, or sets, the hydrated lime.

THE SECOND: Lime has no hydraulic cementitious properties on its own, but in the presence of water and pozzolan (pumice), a pozzolanic reaction occurs and Calcium Silicate Hydrate (CSH) is formed. CSH is the chemical binder that makes concrete what it is. This binding glue further strengthens the limestone being formed as the hydrated-lime-to-limestone curing process takes place, resulting in a plaster that melds the compressive and bond strength of hydraulic cement and the breathing, self-healing, enduring flexibility inherent in lime plasters and mortars.

The lime+pumice+water formulation works beautifully! It has worked for millennia, as the evidence readily attests. Why? Because 100% of the lime is converted to the cementitious binder CSH. This simple lime + pozzolan + water combination triggers none of the deleterious by-products that make modern plaster, mortar and concrete—made using Portland cement—so problematic and short-lived. Thus, Roman methods produce densified, flexible, self-healing mortars and plasters that are not nearly as susceptible to brittleness, chemical attacks, and other problems that plague modern cement products.

SUSTAINABLE AND GREEN. Simple water + lime + pumice pozzolan cementitious finishes not only out-perform modern equivalents, they stand as environmentally sound alternatives to synthetic stucco and other Portland cement-based products. Unlike the energy-intensive process to produce Portland cement, hydrated lime is obtained by low-temperature firing. As for the pozzolan component, our pozzolan is made by mining and crushing a clean, pure pumice—an amorphous white silica, created by volcanic events millennia ago. Pumice pozzolan is not a by-product of a pollution control processes and contains no hazardous materials. Recent studies corroborated previous test data indicating that natural pumice pozzolans are free of Crystalline Silica and other hazardous materials

Almost two thousand years after it was built, the Pantheon's dome is still the world's largest unreinforced concrete dome; built with a lime/pumice concrete, no OPC or rebar.

romepantheon