My wife has been coming here for a while and we're thinking of the bale construction for a new place when we get some property in Arizona. It seems to me that the bales would either break down after a period of time or would settle, leaving vacant space in the wall. Is that a concern or am I not understanding some part of the process that would prevent the natural breakdown over time?
Here is some of my most recent post on SB and related subjects that you may find useful...Let me know if I can answer other questions...
Raised Earth Foundations
Condensation, and other moisture related challenges in natural building...
Cob in Southern Arizona...
Rebecca Norman wrote:My friend who spent a few months at Yestermorrow in Vermont learning about natural building techniques helped tear down a straw bale wall that had been built and plastered as part of a course there. He said there were large hollow areas where mice had gotten in. As I know that mice do make holes in (natural) plaster, and plaster does eventually chip or lose bits, and as I have learned that mice do come and go in one's house over the years, I think this is a serious issue. I haven't heard much about straw bale building that sounds better than straight-up earth building in its various forms (of which I am a resident and long time fan), and mice would be a serious disadvantage.
How long had the wall been up? was it put up in an unprotected area? I would like to know more details about this. Rodents and such (hornets, scorpions) were one reason why I was thinking about using some kind of concrete covering for straw.
Well this conversation just took a turn that has been coming for a while...I was going to post here...but...Tom then added questions that do need to be addressed and one of the reasons I really don't overly recommend SB architecture anymore to DIYers unless they have money and great attention to detail...I have several new topic posts started but I will jump this one up...
Look for a post soon entitled:
Straw Bale Architecture and Pest Control...
In terms of protecting the house, I was thinking that tiling the house would do a good job of that. Most houses in China are made of brick, then covered with mortar and then tiled. A good tile keeps a nice appearance for a very long time with little to no maintenance - just annual inspections. I don't know anything about the carbon footprint for tile, though. I have no problem with stucco but it seems that people are of the mindset that straw houses must be covered with stucco...is that correct?
Bales may settle if load bearing, just like a log home does. Same methods work to deal with it. If using them as in full on a timber frame, you can pack them tight enough to not create gaps if they do settle. But they shouldn't settle with no weight on them.
Well I have started that post I suggest at...Straw Bale Architecture and Pest Control...
On some current points, It is my experience that dipping a bale in fluid of any kind is not a good practice as the interstitial zones may only get wet and not actually receive the saturation of treatment materials intended. There has been some "experimentation with "wetting field straw" with chemical treatments yet this too seems to be logistically and functionally not as effective as "physical management" and or "dusting methods" which of course are dry.
"Stucco" is a term more commonly used here in the North America. It is also...back in the 70's...where issues started. Folks wanted to "render" the walls (like in the U.K. and Europe.) The question then was asked..."What is Render?" Answer..."Render is like Stucco..."
Stucco in North America (cement based) is...NOTHING LIKE...the plasters and renders of Europe which are either clay and/or lime based. Now we all got off to a bad start "Stuccoing" our SB architecture...which of course is OPC based materials and completely inadequate for use on natural buildings... Its important we do not ever confuse this, and most of us in the business do not use the term Stucco...but plaster or render instead...
Tom Connolly wrote:...Most houses in China are made of brick, then covered with mortar and then tiled. A good tile keeps a nice appearance for a very long time with little to no maintenance - just annual inspections...
This conversation seems to be spinning off several different new posts that I have yet to finish and/or started.
I agree that many "modern" structures in China are Cement comprised of OPC (many changing over to magnesium oxides bases) yet I am not sure it would be accurate to say that "most houses" are tiled? Unless I am confused and this reference is to the roof? Most are actually cobb of some form of infill in timber frame, or clay plaster over brick...and again...structurally a timber frame in many areas (most rural area?) of China. The traditional fire proof storehouses of China, Korea and Japan often given the appearance of tile or a tile and lime render method.
Namako-kabe なまこ壁 (Sea cucumber wall) which also incompasses...you guessed it...stucco. BUT...this is Japanese or Asian stucco, and that is actually better translated as..."render or plaster." Furthermore...it is lime based...and called Shikkui 漆喰 (render, plaster or lime stucco.)
If I missed anything...let me know. I will be posting soon on both Namako-kabe and Shikkui.
Tom Connolly wrote:In the cities, during the 80's and 90's, many of the shorter buildings (up to 7 stories) had the walls covered with tile. In the suburbs, this practice is still continued - actually is still continued in the cities but the tiles are often quite large, or are made to look like brick or some other more expensive material.
That is what I thought was being referenced. These are modern OPC based buildings with non permeable walls and have little or no modalities that would be applicable to traditional or natural architecture. Many of these structures and the suburbs they are in are being razed or considered for reformation do to the overall lack of durability in the materials, and the poor city planning that built them. Even within the political systems of China the 'reconsideration' of vernacular systems is being strongly re-evaluated. Historic wooden bridges and buildings are now getting funding, and even new structures in the old vernacular systems are being built instead of concrete and steel.
As I had referenced above, there are vernacular systems of lime and tile that may have 'some' applicability to SB architecture, yet most would create a condensation and low permeability issue if not well designed and understood.
1. Moisture content cannot exceed 20% by weight.
2. Bales shall have a minimum dry density of 6.5 pounds per cubic foot (104 kg/cubic meter). The dry density shall be calculated by subtracting the weight of the moisture in pounds (kg) from the actual bale weight and dividing by the volume of the bale in cubic feet (cubic meters). At least 2 percent and not less than five bales to be used shall be randomly selected and tested on site.
A 16" x 18” x 32” bale weighs around 35-lbs. The weight of the stacked bales can cause settling without being load bearing. The bottom bale of 6 can see 175 lbs. The reaction to the load will depend on alot of factors.
3. Height of walls
4. The compression rating of the wall determine by cube test per ASTM C 109.
5. How well the design transfers loads to the skins/frame, not bales, from roof to mesh to walls to sills to foundation.
6. Pinning & staggering (to prevent misalignment and buckling, uneven compression, from lateral loads)
7. Bond beam (upper sill that distributes even load across the bales).
8. Thickness of wall.
9. Percentage of fenestration.
10. Pre-compression, a min of 100 plf (1459 N/m). Ratchet straps over a bond beam work well prior to render so the skins see no pre-load from the skins to the bales, and transfer load better from the roof to the foundation.
As far as mice, etc, that will depend on the level of detailing and sealing, openings, (mesh, density of the skins, etc) . This is part of the reason I prefer strawcrete, lime binder or clay slip, there is no way mice will eat it, ants can get in perhaps, but the binder seals and binds to the wood frame, etc….For it or render I use type n “stucco” or "mortar" found at home depot, Lowes, etc $10/ 80 lb bags…It has high calcium oxide (lime) 86%+ and is not as strong as type s which has less CO and more MGO. Binder-to-straw ratio determines R-value and compression/shear strength. If you are wanting to keep mice from eating it (which I am not convinced they like it) use type "s" it has more MGO and is stronger. Type N is better if applied in high humidity. I hate to suggest it but, if you really want to keep them from eating it and transfer more load to the skins less settling of the bales, add around 10% Portland cement. If you want better than all this, render using Magnesium Oxide or board if you get your hands on it.
Yestermoore is a good school...Some instructor's wrote a good book I read that covers all this and how to keep bales from settling, there is some good pictures in it on pre-compression and DVD that takes you to the real job-sites: http://www.chelseagreen.com/bookstore/item/the_natural_building_companion:paperback%20+%20dvd