Brant Foster

What if... I substitute perlite or vermiculite for the sand and poured the form without packing the mold. Maybe only using a concrete vibratory to settle it in gently. Just aggregate and sodium silicate binder? It would be much lighter and more insulated. As is, my forms will hold just over 10 cubic feet of sand and will weigh over 300 lbs.

Due to the higher expansion of perlite when heated, won't this cause cracking with the expansion and contraction over time?

Sodium silicate and sand is frequently used in foundries as crucibles to melt cast iron and aluminum for casting. Holds up very well to extreme heat.

Once the brick dome is placed over my core, some of the heat should be reflecting back towards the stack. Can't hurt the lesser insulating sand and sodium silicate.

One thing I've noticed all over you tube is people using perlite tend to crush it when packing a mold. It loses its effectiveness when packed.

Just finished my exhaust port and the outer box to the mold. Going to finish the stack extension tonight after dinner.


I have another idea for the combustion chamber that I can do later. I'll add a "speed bump" out of half round sodium silicate along the bottom. It'll maintain the same cross sectional area while allowing the fast ignition.

Thanks for the input!

This is my inner form for my RMH combustion chamber and riser. I will be casting with a dense/packed mix of sodium silicate and sand. Is 4" of casting enough to insulate the riser to get complete combustion? It's a 6" system.

I built this out of scrap wood because it's going to be burned out when casting is done.

Any comments about design are definitely welcomed. The horizontal run is slanted to create an instant draft when getting it started.

Thanks in advance!
Brant