pumice stone as insulation material...

I've been thinking about a natural insulation/structural material that is not disturbed by humidity within the walls, and wondered if anyone has heard of using pumice? Here in western Washington we have access to a lot of volcanic material such as pumice (though it does have to be trucked over from the east side of the mountains). I've been thinking that pumice mixed with a little ceramicrete or mortar, then poured into forms, might make an excellent structural and insulated wall system. Many people use pumice for insulating their wood fired ovens, why not a whole house?

Mark Anderson : At the bottom of this page check out the " Similar Threads " Toolbox. If you have a good source for Pumice there are many ways to integrate it into a building
structure, Cob being just one of them.

You will learn a great deal about building to allow the free flow of moisture through your structure, any environment that you create has a potential to harbor other beasties
that like similar Temps/Humidity , and porous walls can become incredible reservoirs for them !

Several years ago, ceramic filter elements for Hand carried camping type water 'purifiers ' Led to serious enter-gastric issues and death when the Filters were not cleaned
properly between camping trips and became Petri Dishes for germ propagation !

Nothing that I have said should in any way diminish your enthusiasm for using a great insulating material that is very common in some very large areas of he Pacific Northwest !

For the good of the Craft! Think like Fire!, Flow like a Gas, Don't be the marshmallow ! As always, your comments, and questions are solicited and Welcome big AL

I can think of three ways one might use pumice for insulation and I think the walls would be the least effective. The materials R value depends on how much air it traps. Little pieces would be better than big.

Under a slab seems like natural fit because you generally have to have gravel under there anyway. Perhaps you use pumice instead of gravel and end up with a capillary break that has insulation value as well.

It also seems like insulating at the ceiling plane of a ventilated attic would be a good fit. Most importantly though, air-seal the ceiling plane prior to adding insulation.

I think the walls would be the least effective because its still only acting as a cavity insulation in a traditional framed structure. Cavity insulation in general is a weak insulating practice because of the thermal bridging effect of the framing and susceptibility to air leaks. To be most effective, the cavity insulation would need to be air sealed on all six sides. If you could make the pumice into one continuous plane on the exterior of the structure then it could perform pretty well but good luck coming up with a time and cost-effective way of doing it. Perhaps it could work with a double stud wall or double wall of cord wood.

Forget about mixing it with concrete or mortar. It would become more of a thermal mass than insulation.

pumice can be used in earth bags/hyperadobe/superadobe

http://www.earthbagbuilding.com/articles/pumice.htm

Cool. Also found this from Oak Ridge National Labs http://web.ornl.gov/sci/roofs+walls/AWT/HotboxTest/AdobeEarth/Pumice/

Pretty disappointing R values. R11 in a 16" thick wall. This wouldnt even meet 2009 minimum building codes (poorest performance allowed by law) anywhere in the US. If its really R.68 per inch you would need a 19" thick wall to meet the poorest performance allowed by law in zones 1 and 2 of the 2012 IECC. Ouch!

Thank you for the responses! It sounds like pumice could work as an integrated wall system if 4" of foam panel were put in the middle part of the forms in a 16" thick wall, which is thinner than a straw bale wall. My thought was that a mineral material such as pumice would have some advantages over straw bales in certain applications, though I do plan on using straw bales in my house project.

Check out limecrete demonstrations in UK. Interchangeable with expanded clay in permeable floor systems if I understand correctly.

4" of foam is about r16+ of insulation. If you're going to use it why wouldn't it just be on the outside where it has more effect?