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Natural plasters for inside of rammed earth  RSS feed

 
Frank Troy
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Location: Portugal
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Hello all, and let me apologize if this post is redundant...but I didn't find anything about this specifically in the forum.

I'm currently planning a 60 m2 house out of rammed earth in N. Portugal, an area that receives a lot of precipitation over the winter–very humid–but the summers dry out. I see so many concrete structures with humidity problems (among other things) so rammed earth immediately appeals to me. However, I'd like to find a good finish for the inside of the walls that's breathable (if that's the right word) so that I can fully take advantage of the humidity-regulating properties of the rammed earth.

N.B. I have very little experience building, but I've got a voracious interest and have been researching every spare moment. The house will be on a north slope, with the lower part of the south wall butted up against an earth berm. It'll be heated by a RMH and I'm thinking of using cob for the floor.

Thanks for any and all input. I've been reading the other posts with enthusiasm!
 
Dan Chiras
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Earthen plasters will work extremely well on rammed earth...although many people prefer to leave the interior rammed earth walls unplastered because they are so beautiful. Earthen plasters will help control moisture, as they absorb some moisture from the atmosphere, then release it when atmospheric humidity decreases. Good ventilation can also help enormously. I am assuming the problems people are having is with moisture building up on interior wall surfaces then causing mold. One of the reasons this occurs is not so much because of high moisture levels but because the walls are cold and atmospheric moisture condenses on walls...So, the lesson here is to be sure the walls stay warm. If you build with rammed earth, you will want to build very thick walls. You may even want to include some insulation in the interior of the wall to prevent the walls from getting too cold, which will cause moisture to condense on them.
 
Frank Troy
Posts: 6
Location: Portugal
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Thanks for the great reply! After looking at the site again yesterday, we are now leaning towards taking advantage of some granite walls (about 50 cm thick) already standing, and building the rammed earth walls inside the granite with spacing in between them to let moisture drain. I feel like this could help keep the interior walls warm and minimize the amount of heating/cooling we have to do. This should also minimize the exposure of the rammed earth to the elements.
 
I agree. Here's the link: https://richsoil.com/wood-heat.jsp
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