Insulation for RMH

Built the mock up/ test burn yesterday out of heavy fire brick. Im thinking of next stage now, how well would sand work around the burn tunnel /lower riser as an insulator thinking boxing it in with plywwod or maybe wonder board /durarock etc and then poring sand around it main reason sand = free, perlite while a much better insulator not free.
Gary.

At $10 for an enormous bag it was nearly free when I bought it, however not sure how readily available it is everywhere.

Isailli Hatfield wrote:main reason sand = free, perlite while a much better insulator not free.

Gary,
There's a simple answer: you need insulation which is heat-resistant at the same time. Sand is heat-resistant but no insulator, at all. It's quite good as mass when mixed with clay slip, dry it isn't useful for neither purpose.

Have you tried vermiculite?

Where do yo get vermiculite?

vermiculite is available at "big box" home centers as loose fill insulation in large! bags, perlite is in their garden center...

Not around here this time of year. I found a small bag at Ace hardware about the size of 12 oz of potato chips for $15 most of the nursery's are shut down till spring. what about a mason supply
I think only lowes has blown in insulation but it is cellulose not vermiculite nothing at the depot but fiberglass.