This new insulated earthbag idea is from Chris, one of our readers.
“Feel free to post away with the idea–after all, ideas are to be shared not owned. It seems like a good way to efficiently build thermal mass inside insulation, while being another (simpler? faster?) alternative to compartmentalized-sewn bags or laying inner and outer bags. Hopefully your readers can bounce it around and maybe think of some efficient method/uses for a separated fill earthbag idea.
I am thinking more insulation than thermal mass for the wide temperature range of my mountain environment, and naturally favored a scoria route for a while. After thinking about cast stone/scoria EB and the history of pumicecrete, I wondered if a division similar to eternally solar EB would be better, with thermal cast stone inside and scoria outside. It would seem simple enough to place a ‘divider’ in the bag when filling one side with cast stone or any thermal mass and one side with insulation and then pull the divider, close and tamp as normal. I’m thinking maybe the lower half of the dome would be more appropriate than the corbelled upper part wherein the weight would be hanging inside the previous layer while only leaving lightweight insulation above previous layer…
It seems that separating thermal mass and insulation would be more effective than one insulative pumicecrete type fill (no experience there though). And if so, the divider in the bag while filling seems easier than sewing a divider in a bag, laying two separate bags, or spreading a thick layer of thermal mass on the inner plaster…”
Owen: Great idea. I think you’re onto something. Previously, I thought a temporary divider for filling bags would be cumbersome and cause a lot of the material to get mixed together. But the way you explain it, it sounds very do-able. I hope you can make at least one sample and send me some documentation of your results. High resolution pics are preferred. If it works, I’ll put it on the blog and maybe the next (2nd) earthbag book if that’s okay with you.
– You can adjust the ratio of materials to match your climate (more insulation in cold areas, less in milder climates).
– Scoria’s R-value is not real high so probably better to add extra
– It doesn’t take much thermal mass to create a flywheel effect. Thick plaster and insulated mass floors is typically sufficient. But you need to hold everything together with lots of twine, etc. You could leave out the geopolymer in the bag and use all scoria.
– Measure the quantity on each side so the walls stay level (ex: 1 bucket geopolymer, 3 buckets scoria, etc)
– The geopolymer will compact, but the insulation won’t (or very little). Add extra geopolymer to compensate.
– Add baling twine, especially on upper courses of scoria to tie everything together. This is shown in Kelly Hart’s free dome building guide.
– Clean 1/2″ scoria is preferred.