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Philip Nafziger
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Location: Columbia, Ky
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My avid straw-bale construction enthusiasm is definitely being replaced with straw clay slip as I look into it more. Framing for it seems like cake, and the process of making slip (mud water), mixing it with straw, and packing it into a form seems to good to be true.

Can anyone add insight into this situation. I have a structure that I am planning on having board and batten on the exterior and I want to do the falls with straw clay slip. Can I use the board and battens as my outside wall form?

In straw-bale I think it would be recommended to coat the exterior of the bales with a base coat of mud or something to prevent fire, rodents and insects before applying an exterior like wood, so i was just wondering if the straw clay slip is similar in that regard.

Thanks, Phil

 
Jami McBride
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Can I use the board and battens as my outside wall form?


Yes, but you don't need to.
In this case you would use a lime plaster over the batten, much as they used to do before sheet rock to finish walls.

Clay straw slip takes longer to dry than any other method and with battens it will take a bit longer still. Personally I would use forms, fill with the slip, remove the forms and allow to dry before coming back to finish the walls on either side. Air movement and humidly or lack there of will be the major factors in the speed at which you can add new layers and finish your project. There are lots of good youtube videos and information on building with slip-straw. And it goes by different names such as light straw clay, slip straw, slip clay, clay slip, etc.....

No, slip straw is not the same build as straw bale or solid cob for that matter. Each has it's own best methods and particulars, however all should be finished on both sides for best results. Usually with a natural breathable lime plaster. Even adobe brick, long ago, was finished with lime plaster or lime wash to help prevent erosion or compromise of the walls.

Look into Natural Plasters for the recipes and how they differ from straight cob or slip-clay (search Permies). You will find that they are more water resistant and protective in nature, and will not dust off like clay will all over your house. They do however require something to hang on to, hence the batten in stick build construction walls.

Remember: you do not need permanent external support (battens) for any of the natural building method(s) walls, nor for lime plasters as they will stick to rough straw, cob, slip well enough. You will need internal stabilizers (straw mostly) knitting your wall together, which can differ depending on the wall method you use. They used sticks and boards/poles in the slip-clay in traditional Tudor style houses as the 'bones'. Think - good boots, hats, skin and bones



 
Philip Nafziger
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Location: Columbia, Ky
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Thanks for the reply! We are talking about two different battens. Here is a link to board and battens on a barn, similar to what my structure will look like on the outside.

I am steering clear of the lime plaster on the exterior based on price, availability, skill, and time it takes to do it. Board and batten, while not being as long lasting, is locally available, fairly cheap, quick and easy for me to install. Tho I will be planning either a lime plaster or earthen plaster on the inside over the clay slip.

You have a good point about the clay slip (not straw clay slip ) needing to adequately dry out. The board and battens definitely could hinder that... If it would cause issues, then I would need to just form up the outside walls, take them off, then install the board and battens.

 
Jami McBride
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Awh, we call that 'siding' in my neck of the woods I was picturing more of a lath with gaps. The article I read called it batten, how funny.

The added water to the clay slip does add extra drying time, and possible issues if complete drying is not achieved.

Thanks for the pic, it explained so well how you plan to finish your walls. I'll attach it here for others to see -





endearing-antique-barnwood-brown-rough-siding.jpg
[Thumbnail for endearing-antique-barnwood-brown-rough-siding.jpg]
 
Terry Ruth
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Does anyone remember the video of a doctor that did a presentation of clay-slip fungi and microbial contamination and how to avoid building it into walls? I had it bookmarked until chrome changed bookmark software and I lost them all. Made me so mad

Philip. am I missing something why not use the board and batten exterior as forms? The inside forms could be anything like sheets of 4x8...since you are coming back with a plaster they do not need to be smooth. How thick and what climate zone winter average lows, highs, humidity? I been in KY once if I remember right hot humid summers? The best way to dry is solar or radiant heater, thats why these methods are seasonally limited and most production builders are not real interested. If I remember right that Dr shows how most build fungi into their walls and it has to do with the proper materials and ratios and drying speeds. Clay-slip is not something to just slap together and hope for the best, lab test are really needed and a production process the Doctor had defined. There are also plastic indexes and ideal fung resistant types of clay such as a moderate in the range of 15-35 PI, if it expands_shrinks alot cracks will occur like any concrete that building flex can also cause in the wall welcoming microbial growth along with high humidity. If you read my IAQ thread you will see most microbials live in walls and concrete insulation types are very susceptible. Ideally molecular sieve sixes that will have a decent hygroscopic finished pore if the sub-mix keeps them from crackng, the thickness and density will determine the mass effect. Walls facing the sun may want to be thicker, or high humidity less dense. I think as far as resistance goes r-1.6/inch at best that video went over, not as high a strawbale no where close double that, but the hygroscopic mass can make up the difference depending on climate, depending on the mix, cladding pore size. At the surface a pore size of 2-50 nanometers stops most water but allows vapor drying. Bill Bradbury has some surface lime burnishing techniques, or sealers, you can read about on the breathable walls thread.

I'd leave some ventilation gaps to ground and out the soffit_ridge vents behind the boards and batts so drying can occur in that direction if need be but, now form work has to be pulled...have large overhangs so water cannot get into the wall, slopes at least 30% grade. If it is super humid there and no wind I'd rethink that one. Understand how the coating's on fasteners are going to react with the mixes.
 
Martin Jelenc
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The real question is why would you go through all the work of light straw clay with risk of problems and poor insulation value? My shop-and ideal construction method- is ext B&B with dense pack cellulose for a mold and bug free superinsulated wall, at low cost. With white oak B&B, sawn locally, you have a wall that will last many decades, likely a century, with no maintenance if done right.
I see this is an old thread-what did you finally do, Phil?
Martin
 
Terry Ruth
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Clay slip done right has lab pre-soil test samples to determine PI (plastic index), Shrinkage Index (SI), Moisture Index (MI), and test core samples sent back to the lab to get mechanical and physical properties prior to installation, in other words, it is Engineered not guessed at and labor intensive. These test are necessary for the foundation anyway, the site clay can be taken from depths at around 12-18" depending on soils, do not use top soils unless they pass the test. After that production (mixing, etc) has to be quality controlled to the test results, Ph levels also need to be tested, <14 best. The myth is anyone can do it and history says so but, we don't have all the facts on historical buildings mixes, maintenance records, microbial growths, environment loads, designs, specifics, that can vary drastically!

Modern dense packed cellulose has settling issues, and after the borate and/or borax acidic fire retardants that can be toxic and emit to IAQ, the burn rate (2 hrs), inertness, chem stability with other layers, and MI properties are still not there, well designed clay is MUCH better in MI. If it is installation at around 3-lbs/ft3 (typical standard, very difficult to test and quantify), highly depends on installer experience) will have an r-value of around 3/inch as straw @ 6-lbs/ft3 bale density/weight per 2015 IRC code, since it has shorter fibers but, it will more than likely settle over time at the upper sill or energy truss heels which is a must in this climate zone. 5-lb/ft3 will more than likely thermally bridge @ R-2/inch at best, in this climate zone, again, where is the installed core sample test to verify it's density? If dense packed does create convective moist loops which it is known for(lots of data on the internet to view), air loops or low r-value air barriers it will react the same as cracked slip, but, even worse allowing moist convective loops into wall cavities one can only hope the levels of borate resist(unlikely not designed for it), coupled by a lack of costly strict air sealing (verified by blower door test lower than 1 ACH @ 50 pascals), clay binders provide by default, add denser thermal bridges loss of hvac especially in cold winters, causing rot of the insulation, wood, IAQ, high HVAC loads. 2015 IRC appendix S or R I think it is has a clay slip code path to follow, certain clay's out perform wood by far in wet climate zones due to ability to hold and store/release vapor/liquid water on the order over 30% by weight, use code, much better than guessing and get the test noted.

All this is covered along with all the data in the threads I noted above, no need to guess. You'll see that tight fitted (no settling) inert rock/slag mineral wool insulation core (use code min add r-5-10 if in harsh climates) with tested burn rate of 4+ hours, and properly designed-built clay or lime interior skins out performs dense packed and clay slip cores for the money in all properties. If you want BB siding use the ventilation gap I noted above of at least 3" air gap and follow the mineral wool manufactures design guides for the outer layers, other than the use of plastic barriers(poly sheets, latex paints, etc) (we have alternatives for that noted in the threads).

Hope that helps and good luck with your builds
 
Jay C. White Cloud
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Hi Phil,

My 2ยข...I have made "light cobb" my number one insulative choice for natural building as this system works alone and in concert so well with so many other systems that I see little to match it in overall comparison. Of all the traditional/natural (t/n) systems I have studied, and employed over the last 30 years, this has moved to the very top over the last 20 years...

My avid straw-bale construction enthusiasm is definitely being replaced with straw clay slip as I look into it more. Framing for it seems like cake, and the process of making slip (mud water), mixing it with straw, and packing it into a form seems to good to be true.


Remember you can replace the straw with hemp hurd, sawdust, wood chip, ground or layered old felt carpet padding and even ground new paper (aka cellulose insulation) in various density configurations and forms. This entire "light cobb" system is very ancient in orgin and flexibility of design...

Can anyone add insight into this situation. I have a structure that I am planning on having board and batten on the exterior and I want to do the falls with straw clay slip. Can I use the board and battens as my outside wall form?


Absolutely you can!! I still would recommend a "rainscreen" system to mount your b&b to, but this type of finish is more that plausible. I would need to know more specifics to give and detail advice or make further recommendations...

I do not discount the value and beautiful aesthetics of lime and/or cobb "renders" for exteriors and "plasters" for the interiors, yet the "comparative logistics" of labor, cost and time is much different when we compare wood and these earth based finishing treatments to one another...

Wood...when readily available to a building site...is simply faster, and more enduring with less maintenance in many traditional design formats wood can be applied in. I have removed wood board siding from vintage structures that have only one coat of lime/iron oxide paint on them and they served well their "protective function," with no other maintence, for the barns and homes they had been on for over 300 years!! I love earth based plasters but they can't match this for an exteriors finish cladding, without proper annual checkups and maintenance greater than wood requires in many traditional wood cladding application styles from boards to shake shingle...I have done both and earth/lime is much more labor intensive to facilitate comparatively.... The only thing I know of to beat wood for durability is stone/slate cladding systems...

In straw-bale I think it would be recommended to coat the exterior of the bales with a base coat of mud or something to prevent fire, rodents and insects before applying an exterior like wood, so i was just wondering if the straw clay slip is similar in that regard.


"Fire load" issues and "pests" are often a misnomer in this architectural application format. Properly packed and laid straw bale "DO NOT BURN"...they smoke and smolder if the combustion source is removed, and/or no loose straw is around. Architectural configurations are amplified by modern materials and furnishing as the primary fire load source to the structure, and not the "building materials themselves. Also...there are nontoxic spray fire retarders that make this issue moot anyway. As for pest, that is all about good design, understanding and proper maintenance...not just "plastering the bales."

On some other points...

..Clay straw slip takes longer to dry than any other method and with battens it will take a bit longer still. Personally I would use forms, fill with the slip, remove the forms and allow to dry before coming back to finish the walls on either side...


This is true depending on design system employed...There are alternatives to the above that I would recommend that will dry just as fast or faster depending on wall void thickness, matrix density, fiber type, and saturation level...

No, slip straw is not the same build as straw bale or solid cob for that matter. Each has it's own best methods and particulars, however all should be finished on both sides for best results. Usually with a natural breathable lime plaster. Even adobe brick, long ago, was finished with lime plaster or lime wash to help prevent erosion or compromise of the walls.


Hmmm...I agree that they are not the same generally perhaps, but it all depends on the SB and whether it is being employed by an experience professional natural builder for a structural build or a novice with no PE design abilities and background. The two systems are similar enough that I have become a positive advocate for "light cobb" when compared (big picture) to SB architecture...in most design applications LC beats SB every time... Unless a building site has zero trees, and a straw producing grain crop next door, I don't ever recommend SB buildings at this point...as my first choice...

Remember: you do not need permanent external support (battens) for any of the natural building method(s) walls, nor for lime plasters as they will stick to rough straw, cob, slip well enough.


OOOhhh....I think I maybe misreading this, but I would never recommend a traditional render ever being applied to a substrate alone...even straw bale. These materials (lime and/or cobb mixes) both need an armature to be done properly and in an enduring fashion. I can't even begin to tell you how many "peel offs" and render failures of a similar nature I have seen or had colleagues in the U.K/Europe and Japan tell me about...

Good application practices in natural plasters/renders need a solid armature framework (aka lath or wattle) to function at full potential and in an enduring fashion...in my training and experience...

The real question is why would you go through all the work of light straw clay with risk of problems and poor insulation value?


I have found...in my experience and those of colleagues...that in a comparative balance between "thermal" type insulations and "mass" type (aka flywheel effect) insulations "light cobb" is just about as close to perfect (and most flexible) as I could ask for in most applications if the resources to build with it are available to a building site. Its disregard for "poor insulation" has not been well vetted/proven and seems to be a repeated "concept," base more on assumption and "bad examples," than actual positive applications of the technique. I haven't found anyone that builds with it or has reasonable experience with it and other similar traditional systems comparatively to draw this conclusion about it....but the contrary...They all love it...

Bad design applications are the only time I find issues with the many "light cobb" systems that do fail, but that is a "facilitator failure" and not a material failure...

My shop-and ideal construction method- is ext B&B with dense pack cellulose for a mold and bug free super insulated wall, at low cost. With white oak B&B, sawn locally, you have a wall that will last many decades, likely a century, with no maintenance if done right.


If no modern "house wrap" are employed as part of the above system and a good design elements to the architecture is implemented for ingress/egress pest control management, along with balancing "breathability" for interstitial moisture mitigation comparatively to the "thickness of the wall" I could support this design and have helped with such systems to good affect in some biome types.

However, they are not superior in overall durability of a light cobb timber frame structural design when all the different considerations are examined in my experience. "Dense pack cellulose" does not have the same "free moisture load capacity" as does a "light cobb" matrix, nor does it always effectively migrate interstitial moisture in the same fashion effective fashion as does Light cobbs. This later element is where there is degradation issues in many "dense pack cellulose" systems I have forensically examined over the years, or has been related to me. This is why I no longer recommend this system to clients as a "stand alone" wall/roof diaphragm matrix design comparatively to other systems that simply work much better in my experience...

Terry...good stuff and good points as usual....thanks for those important perspectives...

Regards,

j
 
Terry Ruth
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I found that video....This is the only way I would R&D and control the build to assure I had microb free isotropic properties. I don't have a month to plaster more less three and if in a humid or rain climate longer to put windows and doors in. I also recommend checking code it's not just fire or combustion alot of jurisdictions have smoke requirements, if not following code the Fire Marshal will want to see data. Also if a energy code area where IECC is being enforced R-values will be proven and inspected, look at 2015 IRC if the inspection office has adopted it or allows it other wise a thermal resistance test is needed too which would be wise. I imagine most are in .8 or less range since they did not test and control their mix densities/weight per foot like the DOC. IRC 2012 and 15 have values you add for mass effect.

Too much for me I can think of several better less costly ways to build. Not at the top of my list. I can get all this with interior clay plaster and mineral wool core in a 8" wall in my climate for one, no R&D cost no equipment cost no long lead times to get into the house which can cost too. Also finding the right clay and straw especially will require a season advanced long lead contract with a farmer, shop around as I already did to get golden construction grade bales not left out of the rain not easy here. I get them at $3-5 for small bales here. To each their own




Hats off to the DOC, excellent job IMO. If I were to head this way I'd hire the DOC a PHD Chemist to consult.
 
chad Christopher
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I kinda asked this question before. Build a frame, cover in wood siding, only use a slip form in the inside. I did some tests. It didn't work, not for a home at least. The problems with the test was compaction, drying of the slip substrate, and the lack of a homogeneous surface area when i pulled off the siding and did a scratch test. You don't really save any material by having one side of the form permanent. And it stains the bejebuz out of the siding.
 
Jay C. White Cloud
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First and foremost...anybody considering designing and building with "light cobb" should watch Dr. Piltingsrud's presentation that Terry has posted...it is excellent.

Especially note the section of "jar test for clay content" in the beginning of the video...I warn against this very same thing all the time!! Jar test are basic at best, if not downright misleading...

Also note around minute 14 the 700 year old stray...this illustrates the potential durability of these system if facilitated properly.

He is testing for a 12 inch wall which is a great minimum thickness for a balanced wall system. This can even work well in concert with other insulation types like "mineral wool" board insulation as part of the cladding system inside and/or out...

I don't have a month to plaster more less three and if in a humid or rain climate longer to put windows and doors in. I also recommend checking code it's not just fire or combustion alot of jurisdictions have smoke requirements, if not following code the Fire Marshal will want to see data.


One really needs to follow current trends and research findings as Dr. Piltingsrud has illustrated. As he stated, and I agree...the optimum drying time is about three months..

This is a reason many say they can't employ this system...however the reality I find on most projects is that it's more about good logistical planning than a "don't have a time" issue. Average home takes 6 to 18 months from "ground break" to "turnkey," on good builds that are NOT "throw together" modern spec houses. Planning for these..."3 months to reach optimum drying"...is a matter of good planning and not "can't use," issue. I would also note (as Dr. Piltingsrud has himself) that his test walls used not "mold or fungal inhibitors" at all, and these too can have additional positive effects to this system of building...

Too much for me I think of better less costly ways to build. Not at the top of my list. I can get all this with interior clay plaster and mineral wool core in a 8" wall in my climate. To each their own...


I have to agree with this in certain respects, and comparables...Terry is (correct me if I am wrong my friend as I am doing a bit of "mind reading" here and extrapolation...and speaking for both of us... ) comparing the concept of a "light cobb" wall system as compared to an MMM wall system (Mgo board, mineral wool, MgO board) for overall speed, R value, and cost of construction. I agree with Terry from a "production home built as a spec project" that "light cobb" can not be done on larger homes as cost effectively as MMM walls. Light cobb is a "IYer" material and/or for higher end "spec projects." Hope that made sense to folks...

For a "production system" and "commercial application" of light cobb the system illustrated in this video is probably one of the best for optimum speed and cost. This isn't a requirement per se for a slow pace "IYer" project necessarily. It is all a matter of learning the system well, good design, attention to detail and patients....for either DIY or production projects...

>>>>>>>>>>>>>>>>>>

Hi Chad,

I think I am getting your question...correct me if I am wrong. If asking about making the "form board" permanent to the system...I agree, this is a very bad idea!! The forms only need to be on about 1 to 4 hours on average and then taken off to allow the "light cobb" to dry...
 
Terry Ruth
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Jay, I am impressed how he found that 13 LB/FT3 sweet spot @ R=1.7 and how he maintained it's consistency with the use of designed shear plate plastic tooling with those scoops to disperse the clay on to the straw, and calculated and measured the water ratios based on weights. Sure, a DIY can use a less sophisticated systems but, do not expect the same quality results. He did ALOT of testing prior to and during construction, so if you have that sort of time and money by all means. The only way that makes sense to me is production homes when one can recapture cost at some unit....I mean that is how most business survive. As I said above, this is not something to take lightly (no pun intended just slap together, mix whatever with a fork pick in the back of a barn and hope for the best, to me anyway. Locally sourcing the materials is another hurdle and getting past Building and Safety inspection for the bulk of the people will cost. Price paid for being the manufacture.

I question taking an expansive clay if I remember right some of which can expand up to 40% its volume and trapping it between rigid cladding permanently too. He discussed plasters and stucco that have the same or close expansion/contraction ratios. In my mind, there should be expansion gaps or a chamber, and/or ventilation gaps both on the interior and exterior. 12-14 inch depending on climate and r-value one needs to understand. Perhaps double studded walls or at least some nailers for cabinets, molding, pictures, etc....

I found those temp rises interesting to from microbes metabolizing. Also, how the clay protected not only the straw but wood window and door framing.

PS: I think I am backing out of MGO until the industry stabilizes, rethinking my walls now, unless our friend Ron proves me wrong with the samples coming....But yes properly manufactured MMM would be fast and effective and not so dependent on drying or weather. I'm thinking wood siding, mineral wool, plaster or wood interiors if budgets allows. That is another thread I'l post my plan soon and could use your inputs since I'm not that good with wood and plasters. I know clients may want a smooth interior like drywall has, or troweled. Yes production homes are a different world than DIYs since you have to have options to please a wide range of clients and they want in fast, some are in motels, rentals, that recently sold their homes, school summer breaks and they want to be settled before it starts, etc, and if you can't get them in fast they find someone that can. Clients are probably the biggest reason why most homes are being built in a few months and alot of it is manufactured elsewhere along with high construction loan bank interest to the builder or client. This time of year business is booming winter it slows way down some go out of business. Biggest client the baby boomers these days so that should take some of the kids in school pressures off builders. Yes most are wanting to turn those high interest short amortized construction loans into 30 year low interest fixed asap. Most banks won't go 1 year on construction loans, too risky the build does not get completed.


 
Jay C. White Cloud
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Hey Terry,

I agree, he is one of the best in the "light cobb" movement for really getting the research needed done. I like "light cobb" but will say that I am worried about many out there that are DIYing for exactly the concerns you have. If prudence and good understanding isn't the foremost thought, and only the..."hey this is neat and I was told anyone can do it easy" attitude is very risky. A DIYer can emulate all his steps in a less "mechanized way" but great attention to detail, prototype self tests, and super attention to detail is a must...Most however are many I see are "willynilly" and "oh...this looks o.k. to me" with formula and application...In my view, that won't cut it, and in the view of "old world" traditional cobbers it would either...I couldn't agree more about the "slap it together" part...which is happening too often and could have deleterious affects on the public perspective just like so many straw bale homes that got built sitting directly on concrete slabs and then to make matters worse "rebar pinned" and stuccoed with more concrete...Horrid!! But what gets blamed...yep the Straw Bale...not the idiotic building method...Then SB gets a "bad rap" instead of poor facilitation and design...

I question taking an expansive clay if I remember right some of which can expand up to 40% its volume and trapping it between rigid cladding permanently too. He discussed plasters and stucco that have the same or close expansion/contraction ratios. In my mind, there should be expansion gaps or a chamber, and/or ventilation gaps both on the interior and exterior. 12-14 inch depending on climate and r-value one needs to understand. Perhaps double studded walls or at least some nailers for cabinets, molding, pictures, etc....


I think if you so some built, (well built that is) I think more of this would make sense. There isn't as much clay as you might think in the overall matrix to affect the expansion rate and not all clays expand as badly as that. I distest, as do most traditional plasters the nasty habit that even some "experts" (??) suggest about "directly plastering onto Straw Bale or a "light cobb" wall. Traditional lime and/or cobb plasters must have a solid armature to adhere to such as lathing or similar "wattle work." Leaving this step out is courting disaster at worst and at best having a much less durable system. Many of the "old Chaps" I am still in touch with in the U.K. that are working traditional plasters don't even really care for plastering over old plaster board without "roughing things up a bit..." as they put it...

I found those temp rises interesting to from microbes metabolizing. Also, how the clay protected not only the straw but wood window and door framing.


Clay (and lime to some extent) does an amazing job of acting like a "drying poultice." This is what all the old log cabins started to "rot away" when modern contracts had the brillant "I think" moment to start ripping out all the cobb and lime daubing between the logs and replacing it with concrete...!!! This just killed these fine old buildings. Cobb is much better at "keeping things dry" even when it is humid out...Even really humid!!

PS: I think I am backing out of MGO until the industry stabilizes, rethinking my walls now, unless our friend Ron proves me wrong with the samples coming....But yes properly manufactured MMM would be fast and effective and not so dependent on drying or weather. I'm thinking wood siding, mineral wool, plaster or wood interiors if budgets allows.


Terry, I was wondering about all that, and actually have been working on some "optimal walls" profiles that I hope to post in the next few months that you may find plausible for a "spec house" wall design. I will get it done and posted as soon as I find some time to flesh out more info for it...

Together, and will good feedback from our members here, I am sure a "production wall system" can be had that is both durable, natural and sustainable...while still being cost effective and competitive with other modalities currently on the mainstream market...

Speed is a "cultural thing" also as many clients demand (in some areas...less in other...like here) "instant gratification." That is why timber framing is becoming more and more in demand. The client doesn't see the work to cut and joiner...all they see is a frame show up on a truck with a bunch of trusses for the wall system and in less than a week for most home (even a day to three days from many) they see their house up and reading for finish work and mechanicals/electricals...Many can be done in less than 2 months if the logistics and facilitation team are really "well oiled" and cohesive...Combine this with some mineral wool insulation for the exterior thermal envelope and some other "traditional" elements and we can even get bank financing in most areas...Its all about "good communcaiton skills" (written and verbal) and presenting a cohesive business and design plan. I give great credit to the "Timber Framers Business Council" over the last 20 years for doing such a great job of "nationalizing" timber frame packages and getting them to be competitive in the mainstream market...Quite a few of these are even straw bale and other natural methods...accept really well designed and detailed...

Regards,

j
 
Rebecca Norman
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I'm going to read this whole thread with full attention when I've got more time, but I thought someone might like what we've been doing to enjoy the insulating advantage of straw clay, while having it dry faster than it would as a monolithic rammed-earth wall type of thing, which is how we used to always build at our school. Last year we started making oversized bricks of straw-clay. Often it's more wood shavings than straw, since wood shavings are free waste product around here, whereas straw is a useful resource that is not free or wasted here. This way we can make the big flat straw-clay bricks, let them dry flat on the ground for a few days, then turn them up on one narrow side to dry more, so that when we build with them they're already mostly dry.
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Jay C. White Cloud
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Hi Rebecca,

Great photos and method to share...

I would love to read your thoughts when you do get around to reading this thread...

I akin your "adobe block light cobb" to one of the...more adobe (aka cobb) than the light part...??

I only presume yours is more "adobe block" than a actual light cobb that is being mixed by Doug (et. al.) for his tests, and method of construction as his light cobb mixes are not capable of taking any loads at all. When this mix matrix is in the correct proportions for insulative properties, whether infill or block modality which I do really do like, they can't meet..."load parameters for a structural wall diaphragm"...as illustrated in your great photos...

I think for some design types, DIY projects, and for accelerated drying this...block method...has great promise. Because of the time to handle materials logistically it will be more labor intensive than infill methods, and because of the requirements of the "cobb mortar," the walls will be denser and present with some thermal bridging issues that...may or maynot...need to be addressed. If the blocks are made to the prescribed densities for actual...light cobb...they still can not be employed in a "structural wall" with them as illustrated in the photos.

Please correct me if I am in error, the school project design was examined (guided?) by a PE for those structures. I thought I remember reading that...didn't I? Did a PE look at this design for these adobe block walls?? I don't see any structural framing and it looks like all roof and tectonic loads must be endured by the walls alone? I also don't see any "ramparting," or "strengthenings" within the wall systems to withstand "spread" and "wall diaphragm shift," from normal settling or weather events. Do you know how these "load dynamics" are addressed for your seismically active region? Do you have any photos of them building the foundation system? I would love to see how they manage the drainage and load distribution for the walls...If you have a mix ratio for the blocks that would be great to have also if possible. And, since I am bugging you with probably to many questions (sorry...) I would love to see photos of the roof system and how it is assembled.

Thanks again for posting this here...if you have more photos, and info like the above...this deserves its own post thread outlining the entire project if you could put that together...

Regards,

j

 
Rebecca Norman
gardener
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Location: Ladakh, Indian Himalayas at 10,500 feet, zone 5
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food preservation greening the desert solar trees
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You're right, it's not light straw clay, much more earth than that. I guess since we don't normally use straw in our adobes and rammed, earth, to us this seems like straw clay.

We're only using it in single-story structures. We used it in 2011 as load bearing wall in a storage shed and it has held up perfectly, so last year we used it for the wall of the little single-story house shown above. For seismic stability there's an RCC concrete tie beam around the top of the wall.

We don't have a structural engineer on staff. Our buildings are designed and overseen by a Ladakhi mechanical engineer who has designed and executed and lived in many earthen buildings and also did a masters at CRATerre in France; and an architect who has mostly been building and teaching earth building. Neither of them has worked in the mainstream part of their fields, they're much more Out There all the time, inventing and trying new things.
 
Terry Ruth
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Rebecca, I'd suggest getting an Engineer to look at each and every build since a sheds wall span length can be much different than a home...there is a max span for the wall type to a point where intermittent foundation may be needed to break the span.

Also, since F=MA, Force= Mass X Acceleration, , in seismic when the ground shifts and the wall/roof lags behind the racking/shear effect on the wall/roof is greater with more mass (M, Concrete tie beam-usually for uplift forces and vertical wall/roof even distributions)) at the top of the wall. Next time you run into the mechanical Engineer please provide an explanation of the how their designs are meeting wall, roof, foundation sizing for seismic and wind?
 
Jay C. White Cloud
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Hi Rebecca,

Thanks so much for giving more detail of the build in the shared photos...

This would then be an "adobe block" type structure, and standard practice in many regions of the world (minus the concrete augmentation) and not any form of "light cob" (aka slip form straw clay.)

...We don't have a structural engineer on staff. Our buildings are designed and overseen by a Ladakhi mechanical engineer who has designed and executed and lived in many earthen buildings and also did a masters at CRATerre in France; and an architect who has mostly been building and teaching earth building....Out There all the time, inventing and trying new things..


This sounds exciting, yet as Terry has alluded to, there are sometimes a need to really test out these "inventing and trying new things," before we put them into long term practice with "living occupants." Store houses, and even barn or other outbuildings seem fine for such "experimental methods," as we often see going on with "augmenting" vernacular styles with modern materials...

...RCC concrete tie beam around the top of the wall...


As mentioned above the alteration and augmentation of vernacular buildings with modern materials has demonstrated that this often is not an "improvement" at all, but only a change in the design. These "changes" can lead to unforeseen issues...

"Bond Beaming" or "Bond Beam Tying" is a common practice throughout many mountainous regions...including the Himalayas. Bhatar, Dhajji Dewari, Kath Khuni, Taq, and many more vernacular architectural forms all employ a "bond beam" system of some fashion. Many, in the more seismically active regions use them every few half meter or so up the entire wall to give them even more stability. These of course are made of wood, or is some rare cases long interlocking stone, or bamboo poles of different woven styles encapsulated within the cobb.

Wherever we have seen modern augmentation by OPC cements (which add massive weight and too much rigidity) to vernacular earth structures, we have seen failures with the traditional building designs that have been changed...not improved. The recent April 15 "thrust type" earthquake east of the district of Lamjung demonstrated these negative effects as not all the "native structures" that failed were actually in there original condition and had been "augmented with concretes."

Dr. Langenbach has been a colleague, mentor and friend I have followed and learned from for many decades now...His work in this region and area is well known and respected. I think I have shared his web based information here a few times in different posts, and I believe reading his research and understanding would be strongly beneficial. He has warned many governmental organization and NGO about going into regions and "changing" vernacular buildings to "I think" or "lets try this concept" as very risky in practice if not facilitated by those with "traditional building experience and knowledge." Too many times what we "think" may be a good idea turns out to actually weaken structures...

Traditional is Modern...Vernacular Architecture and Traditional Construction around the world.

Building Conservation Technology

In your case...I see an "internal load wall" that should act (to a degree) as a "rampart" and give the frame some additional strength. My primary concern is the added weight of the "cement bond beam" that are entirely too heavy and "stiff" for adobe block walls in regions with possibly strong or "thrust type" tectonic events...I don't think (this is just my opinion based on photo review and your description) that these structures are in any jeopardy of failure at all. They may see some wall cracking and localized failures within some of the wall or roof diaphragms, but nothing catastrophic is apparent to me from the photos, and I wanted to stress that... I thought I should share that if my post read as too negative...I think those building would be generally o.k. up to a Richter 5 or 6 and only need repare.

Thank you very much again for sharing...I always love reading your posts and seeing the work you are part of...

Regards,

j
 
Philip Nafziger
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Location: Columbia, Ky
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I had no idea that there had been so much action on this thread because I never received any notifications! What a pleasant surprise, thank you everyone for your input.
 
Philip Nafziger
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Location: Columbia, Ky
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Terry Ruth wrote:Philip. am I missing something why not use the board and batten exterior as forms?


This is one of the exact questions I was trying to figure out! According to the video (which is was AWESOME!) Using my Board and Battens as my outside forms would cause issues with white mold forming due to the lack of air circulation. According to Chad Christopher who has tried this, it doesn't work.

Terry Ruth wrote:I'd leave some ventilation gaps to ground and out the soffit_ridge vents behind the boards and battens so drying can occur in that direction if need be but, now form work has to be pulled...have large overhangs so water cannot get into the wall, slopes at least 30% grade. If it is super humid there and no wind I'd rethink that one. Understand how the coating's on fasteners are going to react with the mixes.


Unless of course there could be a way of leaving an air gap as you have mentioned between the exterior and the light clay. Unfortunately, I cannot think of a way to actually make this work.

1. Studs.
2.Lathe (horizontal 2x4's 32' on center attached to the studs)
3. Board and battens (attached to lathe)

If I simply used the B&B as my form, the light clay would be packed directly against it, causing white mold. Also if I could figure out a way to leave a gap between the B&B and the light clay, it still would not be vented but rather trapped air pockets.

Seems like my best option, as has been said, is to use forms for the inside and out then install the B&B.
 
Philip Nafziger
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Location: Columbia, Ky
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Thanks for the 2 cents worth! Can i get anymore pennies out of you?

Jay C. White Cloud wrote:Remember you can replace the straw with hemp hurd, sawdust, wood chip, ground or layered old felt carpet padding and even ground new paper (aka cellulose insulation) in various density configurations and forms. This entire "light cobb" system is very ancient in orgin and flexibility of design...


Very cool! I always love building techniques that can be adapted and implemented in many different cultures and areas of the world. We have a large forestry industry and not as much straw here in south central Ky, so I may seriously consider using wood chips or saw dust.


Jay C. White Cloud wrote:Absolutely you can!! I still would recommend a "rainscreen" system to mount your b&b to, but this type of finish is more that plausible. I would need to know more specifics to give and detail advice or make further recommendations...


Could you elaborate on a "rainscreen"? What specifics would you need to know?

Phil
 
Jay C. White Cloud
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Hey Philip,

"Rainscreens" can be googled but most area "modern" poor example of the traditional...It is simply a "venting space" behind side systems that (in the better forms) ties into the "cold roof." All in all, the two systems work well in concert with one another for "venting" and good air circulation around the exterior portion of a structure and into its attic or roof space area...

Regards,

j
 
I agree. Here's the link: http://richsoil.com/email
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