Another Question About Plastering Straw Bale Walls

Here is an email I received today. My answer is below.
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Andrew,

We have already done the first two coats and wanted specific instruction on
the last as it is the one that will encounter the weather. We have used
ordinary clay, gritty ( lots of facets and sizes of grains) sand and chopped
straw for the first two coats and they were much drier than what you showed
in your DVD. We also didn’t wet down the bales first, but did sponge the first coat
before applying the second. It is very rough so we don’t think we’ll need
the scratch thingy. Our ratio was 3 parts sand to 1 clay and about 1/2
chopped straw. The clay was dry bags purchased through the pottery supplier
in town. It was easier to apply with more clay and we tended to put in less
sand as the walls went along. unfortunately that meant there are a few
cracks now… not really big but there none the less. It seems to be well
stuck on and really hard though. It is weathering were there are direct
winds and rain, mostly the west side of the house.

So really at this point we are just soooo tired and want someone to come do
it and FIX it! We had hoped in the beginning to get someone to use regular
stucco for the final coat and thus have a maintenance free exterior. we have
heard recently though that the mixtures would react differently to climatic
changes and might move or crack relative to each other. what do you think?

Maryann
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Maryann,
I am sorry to hear that you feel you have reached a stopping point. I know how that goes. That said, I think you still have some options to take care of your concerns.

If you have a relatively smooth second coat in place, you can fix the cracks with relative ease. If you have the plastering DVD, go to the scene about floating the brown coat. That is where you use a rubber float to push ad swirl the second coat of plaster into the first. It smooths the surface and strengthens the plaster. If you have already done that, great! If not, you can still do it if you mist down the clay and start floating. This is one joy of clay plasters: you can rework them even after they harden. The same is true for the cracks. You can mist them and float them back into the plaster. For the final coat, I suggest you use a lime plaster with the color in the plaster. This will allow you to finish the plaster in one shot, no need to paint, and will provide a resistant surface for the elements. I suggest Natural Hydraulic Lime if you can fit it into the budget. You can find them at www.limes.us. That will work over the clay with no problem. It is more flexible than cement based plasters ands therefore can handle the movement. This is a thin layer, so the brown coat will need to be smooth before you can apply the lime finish coat. Good luck and make sure to rest your plaster arm. I have a friend who ruined her shoulder by working too hard for too long on plastering walls.

Andrew

5 Responses to Another Question About Plastering Straw Bale Walls

  1. Gene Gosse Sun, September 14, 2008 at 8:39 pm #

    Hi Andrew,

    I was reading your response to Maryann regarding cracks in her clay-based plaster and was wondering if the same technique will work for eliminating cracks in the brown coat of NHL plaster after it has been up for a week or so (misting the plaster and then floating it out)?
    Thanks,

    Gene

  2. Andrew
    Andrew Mon, September 15, 2008 at 8:50 pm #

    Gene,
    You can float out cracks in NHL for a few days as long as you keep the surface misted down the whole time. Once you let it dry, it is hard to get the cracks to float back into the surface. It is always worth trying though! Good luck.

  3. Mark Thu, November 13, 2008 at 10:20 pm #

    Hi Andrew,

    Do you ever use mica in your finish plaster? I read the Natural Plaster Book and it said that mica in a clay slip looked nice. Do you know where to get it?

    Thanks, Mark

  4. Andrew
    Andrew Mon, November 17, 2008 at 8:27 am #

    I have not used mica but have seen it used. It does have a nice look. I would imagine an art supply store or even a landscape yard would have the material, but that is a guess as I have never used it myself.

  5. Steve Winn Tue, May 19, 2009 at 9:36 pm #

    I used Mica flakes in my earthen plaster walls and in the grout for my pavers. Great stuff. Try buidingforhealth.com. The Mica is hard to find on the site. I suggest calling them.

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