Refractory component tips
"Masonry cement" (on the left) is not the same as "Portland cement". Portland cement is plain cement powder and specifically says Portland cement. Masonry cement is a mixture of Portland cement and sand. It may also contain other components (admixtures) to provide a certain characteristic such as waterproofing agents, colors etc. In some cases you only need to add water to masonry cement mixtures.
Fireclay is usually (at least where I buy it) sold in 50lbs (about 23kg) plain packages and they don't even say "fireclay" on them. I get it from a place that exclusively sells masonry supplies for $8.00 (2002 prices). I've never been to a ceramics supply place so I can't say whether or not they sell it. Whip out your phone book and call if your wondering, in fact maybe I'll do that.
Another type of clay is Bentonite clay. I haven't been able to find any where I'm at. I've read that it's available from feed stores and farm supply places. Kitty litter is bentonite clay. But unless you have a big rock tumbler or ball mill I don't expect anyone to use this source. Anyone willing to grind enough kitty litter by hand is a much more patient person them me. I've tried using it whole but it didn't work, however I think I might know a way.
Perlite is a light-weight odorless, sterilized, heat-expanded volcanic mineral. It's used in potting soil to loosen and aerate the soil resulting in strong, branched root development. This is vital to vegetable seedlings because... oh wait, we're talking about refractory... The reason it's so good for refractory formulas is because it doesn't conduct heat very well (heat doesn't pass through readily). A similar product is called "vermiculite" it's added to potting soil because it retains moisture. This quality makes it undesirable for refractory.
The "2 bucks" furnace formula
The refractory mix is composed of Portland cement (1.5 parts), silica sand (2 parts), perlite (1.5 parts) and fireclay (2 parts). The first three components are mixed together thoroughly. I used a 1-gallon bucket to measure the parts. Less than one bag of perlite was necessary for the bucket furnace and I had about a gallon and a quarter of refractory left over.
Tip: Build the body for a coffee can furnace and use the remaining refractory for that. Or mold the remainder into plinth blocks or bricks.
This is what the first three components look like when mixed.
After moistening the first part of the formula, the fireclay is added as seen on the right side.
Here is the refractory as I used it for my "2 bucks" furnace. The mixture was rather loose and gooey but it's as sticky as I don't know what. Rather sloppy to work with also. It should actually be mixed much drier. Keep it just moist enough to hold together neatly. Try for the texture of stiff cookie dough.
This is what the above refractory looked like as I began lining the furnace body.
Here's another look at it.