I needed learn how to make Green Sand for metal casting. If you watched the furnace video you saw me making refractory, and making green sand is about the same process. Simply put, it is a mixture of sand, bentonite clay, and a bit of water.
Since I had some fireclay left over I was going to use it, but after some research I realized that since fireclay vitrifies (fuses) with heat, I probably could not reuse it after I molded something. So I figured I would go with Bentonite (as everyone else does. If you cannot buy bentonite clay in bulk (luckily my ceramics supply store has it), you can grind up clumping kitty litter (cheap without additives) and reclaim the bentonite. It must be ground up VERY FINE and you will need a dust mask.
Bentonite now gets added to a 5-gallon bucket of “fine” masonry sand (I used play sand, but the finer the sand the better quality your castings will be). You need a 1 part clay to 9 parts sand. Mix this dry, and then add water in small increments (like coffee mug sized). Mix between additions over several hours. You want the clay to coat the sand evenly, so the more you mix and the slower you work the happier you will be.
The next thing you need to do is check to make sure the sand is “packable” You can read about this in the Gingery book, or watch my video. Basically you just grab up a handful of sand and squish it in your fist. It should mold to your hand. Then break it in two. If the lump of sand holds its shape and breaks cleanly when you snap it then it’s good to go.
Store this in a covered container (I use 5 Gallon buckets with lids) and the longer you store it (unless it dries out) the better it will be.