[GSBN] Plaster thoughts

Sat Mar 3 23:44:25 UTC 2012

Dear Bruce, Tim and Mark,

Three points:
1. Not knowing what the climate is there (in particular humidity), type of sand (silicate or crushed lime) or clay mineral type, I can only share the if it's dry and the sand is silicate then my experience is that lime washes and thin lime plasters will peel off after the first rains.  I've seen even small amounts of cement cause good clay bricks to disintegrate - I assume because of the type of clay mineral.  I hope that's not what you're finding.
2. For many years we mixed our earth plasters using clay (from dried flood deposits and well drilling tailings), course - sharp sands (no fines - wind eroded Nubian sandstones quarried from sand dunes) and paper fibers -  newspaper, egg crates and cardboards soaked for 24 hours+ and broken down in a cement mixer.  These mud-paper plastered structures, pseudo 'earthship' - tires filled with plastic waste, have stood for 20 years with very little cracking and an amazing ability to get wet and dry out without disintegrating.
3. the exterior coating that we like best is used cooking oil using the ancient Steen 4 coat recipe: 100% oil (applied heavily with rollers), 75% oil + 25% turpentine, 50-50 and finally diluted to 25% oil with 75% turpentine.  We apply them one after another without waiting, best when it's hot and Always after the clay/sand plaster is completely bone dry.

We've found that maxing the sand  component in a final, thin plaster coat without straw creates the hardest protective layer - that's particularly appropriate where people (kids) come in contact with the wall / bench (otherwise they pick at the straw).

Good fortune and feel free to drop in since you're already on the continent.
Alex

Alex Cicelsky ~ Director of Research and Development ~ Center for Creative Ecology ~ www.kibbutzlotan.com/ga<http://www.kibbutzlotan.com/ga>
Kibbutz Lotan ~ D.N. Eilot 88855 Israel ~ Tel: +972-(0)54-979-9009 ~ Email: alex at klotan.co.il<mailto:alex at klotan.co.il>

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From: GSBN-bounces at sustainablesources.com [mailto:GSBN-bounces at sustainablesources.com] On Behalf Of Bruce King
Sent: Saturday, March 03, 2012 19:10
To: Global Straw Building Network
Subject: Re: [GSBN] Plaster thoughts

Marks, funny you should ask!

Tim Owen-Kennedy and I have been roped into working in Kibera (Nairobi) Kenya on the Human Needs Project (http://www.humanneedsproject.org/), one part of which involves renovating earthen huts in the shantytown that is Kibera.  The renovations mostly involve applying a nicer and more durable finish to the badly eroded wattle-and-daub walls.  You can see pics on the website;  their main thing is to build a community center that provides clean toilets, potable water, and solar-powered charging stations for mobile phones.

For the earthen walls, our client came to us already wedded to a cementitious system based on PVA fibers that bond to cement and give concrete/stucco huge flexibility and crack resistance.  Tim's and my job, which we're in the middle of right now, is to devise and test PVA-cement mixes that can bond to the earth & stay put.  We are going to test for delamination in a weather chamber that wildly fluctuates temperature and humidity.  We are acutely aware of the innumerable previous problems all over the world  associated with cement-over-earth, and know we need to have as much vapor permeability as possible,  So far we imagine using only large, course sand (no fines), minimal cement, the PVA fibers (they look like bleached, finely chopped straw), and possibly some lime.  As usual, we have very little time or money to play around.

Well report back to everyone as we progress over the next few months.

Bruce King
bruce at ecobuildnetwork.org<mailto:bruce at ecobuildnetwork.org>
(415) 987-7271

On Mar 3, 2012, at 8:20 AM, huffnpuff at q.com<mailto:huffnpuff at q.com> wrote:

Mark and All,

I am sure you will be aware of some of what I suggest, as it's common knowledge in the earth plaster world. Too much clay, too little sand/aggregate, the size of the sand/aggregate (too fine sand) can all cause excessive cracking. Removing clay, adding more sand/aggregate or upping the size of the sand/aggregate could help. I've found that the more/longer straw added can eliminate higher clay content cracking. I've used a 1:1:1 ratio of clay, long straw, masons sand for a very sticky, super strong, low/no cracking application to stick as a base over foam, lumber and plywood (placing some of this mix on the surface, tack mesh to subsurface, place more mix, for an added mechanical bond).

When you start adding lime and cement to a mix sounds like what we do in the US. If it doesn't move, get a bigger hammer. It's not better living through 'bigger hammer' chemistry. Often less is more. I think you'll find some of your answers to cement earth plaster ratios in a study by the U. of Penn as they attempted to do some repairs to the mortar on ancient ruins in the Mesa Verde and Chaco Canyon adobe structures.http://repository.upenn.edu/cgi/viewcontent.cgi?article=1044&context=hp_theses You'll find test results on "tensile strength, modulus of rupture, water vapor permeability, and water porosity (respectively) (and freeze/thaw) vs. volume-percent of Portland cement for amended mortars" .

Also, you might check out Stabilized Compressed Earth Block sites (adobe block on steroids...it's what happens when engineer types make adobe block). My limited experience with SCEB's is they only use about 6-12% cement...lime may be substituted, but don't quote me. Check out the Auroville Earth Institute  www.earth-auroville.com<http://www.earth-auroville.com/> for mixes using cement. Maybe others can chime in here with knowledge on substituting lime for cement. Of coarse, different areas have different clays that react in varying ways so experimenting with different mixes/ratios would be prudent.  The one advantage of using cement amended earth mixes is that it hardens much faster so the results of your experimenting is swifter.

For a shameless plug for the Conference in Sept. 2012 http://www.strawbaleconference.com/index.html the Auroville Institute will be represented at the conference by a presentation by Richard Presley.

If the locals insist on using cement additives to the earthen plaster mix, visiting the information on these two sites should help with your educated guess as to ratio's. I did some extensive stone work this last summer and wanted to use an earthen mortar. I used a 9:1 mix of my earth plaster mix/cement. My mason buddy thought I was nuts. Eight months later, 4 feet of snow and lots of freeze/thaw in our Colorado winter climate and that mix seems to be holding up amazingly. There's little to no degradation of the mortar.

For those interested in pre-fab straw bale walls and those using cement stucco's these amended earthen mixes may be worth noting.

Hope this helps Mark...Regards,
Mark (see you in September) Schueneman
Colorado Straw Bale Association
303-444-6027 hm.
303-591-9841 cell

________________________________
From: "Mark Jensen" <markj at redfeather.org>
To: GSBN at sustainablesources.com
Sent: Saturday, March 3, 2012 3:44:05 AM
Subject: [GSBN] Plaster thoughts

Hello et al,

I am in Kenya right now working on two straw bale buildings, stacking for both Monday and Tuesday. I am struggling with plaster thoughts. I guess the last plaster they did was clay, sand, cow dung, chopped straw, lime, cement and water. Nobody knows the proportions but they had severe cracking, like a dried up lake bed.

Now they want to do 1 1/2 bags of lime, 1/2 bag cement, 4 wheelbarrows of sand, chopped straw and water. This seems like a recipe for disaster to me. They are on a very short budget. I suggested harvesting clay and just doing a earthen plaster, it's free other than some labor to harvest.

Any thoughts on the recipe above?

Your input would be appreciated.

Asante Sana, Thank you very much,

Mark

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