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insulating a concrete block wall in a bathroom  RSS feed

 
Gilbert Fritz
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We have an un-insulated exterior concrete wall in a bathroom. Hot steam against cold masonry, with a layer of something else in between the two, spells trouble. What can we use to insulate the wall that will not have trouble getting wet?

I was wondering about mixing lime plaster and perlite. Would this work?

We can't use fiberglass, etc because the concrete wall surface will be the interior wall surface as well.
 
Karen Coe
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I went to a workshop a few years ago on using American clay. They have a website detailing this product.
 
S Haze
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Location: Southern Minnesota, USA, zone 4/5
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Is insulating the outside of the block wall a possibility?

By doing so you'd be using the mass of the wall as thermal storage. If you do go this route the only thing I know of to caution you about is that if you live in a very cold climate and the wall and insulation extends below grade the ground outside can freeze and expand pushing in the wall. I heard this from a contractor family member but he said it applies mostly to situations where the soil is very compacted because the house was built long ago and the drainage is poor.

I'd really like to know if clay or plaster on the interior would work in a situation like this or will the differences between these materials' affinity for water and that of the concrete cause problems with its integrity or the buildup of moisture in the wall. This appeals to me more than using a concrete based material if it works good.

I'm also working with a concrete wall (mine is already well insulated on the outside) and considering using a product called thorocoat to cover the interior because it's supposed to have the same permeability to water vapor as the block. I don't know much about it yet in terms of cost or potential hazards, or if it can be mixed with perlite or vermiculite but I'm guessing it could be.
 
Brian Knight
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Is the wall(s) below grade?
 
Gilbert Fritz
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Yes, the wall is below grade.
 
Brian Knight
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Are there termites in Denver?
 
Gilbert Fritz
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There are termites, but they are rather rare, not a big problem overall. (Of course they are a big problem for the individual house that gets them!)
 
Brian Knight
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I like the idea of insulating the outside of such walls because you can take advantage of the thermal mass. Problems are termites and difficulty of detailing the exterior insulation. Iam currently adding foam to the outside my CMU foundation but NOT excavating to address the below grade portions. I always use to recommend doing foam or mineral wool on the outside of foundations. I still currently prefer to do it that way when it makes sense but its very difficult to do right. I think most would be better off following BSC recommendations which has increasingly moved to doing it from the interior instead of the exterior. You lose the thermal mass TM effect but as weve been discussing elsewhere, TM is not as important as other things anyway.

http://www.buildingscience.com/documents/information-sheets/basement-insulation/?searchterm=basement
 
Brian Knight
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Just read a great article on retrofitting exterior insulation in the latest JLC. Folks should check out Dales thread for some good pics of his drainage excavation project. http://www.permies.com.evohst.org/t/31726/green-building/Dale-drainage-customer-house-pictures

I enclosed this link which discusses the issues in detail and page 19,20 discusses a technique used by utility contractors; pressure washing a slot and sucking out the debris with a vacuum. No pics at link like there was in the article..

http://apps1.eere.energy.gov/buildings/publications/pdfs/building_america/excavationless_exterior_found.pdf
 
I agree. Here's the link: http://richsoil.com/email
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