Bentonite, here in MT, is the brand name for the type of diatomaceous earth used for sealing oil well casings, around the perimeter of basements, and incidentally in health and gardening. The two mines in the area are near Belle Fourche, SD and near Worland, WY. I bought 4,000 lbs from Worland to line an irrigation pond and have kept about 100 lbs cause it's cool stuff. The Worland mine is closer, and they crush it to a finer powder. It's also higher in calcium than the bentonite near Belle Fourche. Whatever the reason, I started mixing it with water like I would powdered joint compound (drywall) and was VERY impressed how much water it wanted to get a reasonable slump in the slurry, mixing with my industrial drill in a 5 gal pail. I then hired my grandsons (grandma cookie payment) to help me pack in the perlite in mud pies,to a breaking consistency, and cram in between my two layers of SS 24ga sheetmetal for the burner. That's when I decided on the experiment making a brick in my first RMH. I let it dry about a month before firing it. Does that help? I haven't figured out how to post picts in the place.