Making Green Sand

I've wanted to cast metal for a long time. I've had the equipment, the supplies, green sand, and everything else ready for months now... well, I finally got around to it!

Making Green Sand

Green Sand is used for metal casting. Simply put, it is a mixture of sand, bentonite clay, and a bit of water.

Bentonite is used in clumping cat litter, so to make green sand, I ground up some cat litter in a ball mill of my own design.

The drum is a 5-gallon paint pail, turned at 32 rpm. The grinding media was about 2.5 gallons of crushed granite rocks, ranging in size from 1" to 3". Six pounds of Tidy Cat clumping cat litter were dumped on top of the rocks, and the drum turned for 1.5 hours. This ground the cat liter very finely. (If you do this, wear a dust mask when you handle the bentonite.)

The ground bentonite (I guess you could call it "cat litter flour" - yuck) was added to a 5-gallon bucket of "fine" masonry sand. The bucket contained nine inches of sand, so I added one inch of bentonite to achieve a 10% bentonite mixture, and mixed the two dry for about ten minutes. I added about 32 oz water in six ounce (coffee cup) increments, mixing constantly between additions, over a period of several hours. I stopped adding water when the sand started to display "packability", or whatever you want to call it. Here is my Dave Gingery imitation...

Green Sand

I squashed a handfull of sand into a lump, and broke it in half. It held it shape quite well, and broke cleanly.

Continue to making the mold.


© 2003 W. E. Johns