Perlite

Hello!

I’m trying to find out if horticulture perlite (not treated to be water resistant) is ok for the base insulation under the RMH or must it be the masonry perlite? I will be building on top of a loose rock floor. It’s about 3 inches of various sized rocks getting smaller in size with depth. Under the rock layer is sand. There is not a vapor barrier but I’ve never seen any moisture- although I do live in the Pacific Northwest .....
This question has been asked in this forum before but it went unanswered?

Also, any suggestions on what to do for a base under the mass? Build right on top of the rocks? Do a perlite pad on top of the rocks?In an old post, Erica suggested a semi- dry stack as the first layer to help with keeping things dry. Unfortunately, she didn’t give any info on how or with what material?

Thank you!

Hi Heather;
I have always bought my Perlite from the landscaping company, and I've never had any problems with it.
Mix it with clay, and use a 2x4 form box to create your base.

Under your mass, it depends on whether you have a piped mass or a stratification chamber.
A strat chamber would not need a base, the floor would slowly get a covering of fly ash that would act as an insulator.
The hot air rises to the top and has significantly cooled before reaching the exit a few inches above the floor.
A piped mass should have a cob base to keep the heat moving up into the mass.