Green Sand for Casting

I made my casting sand much like Gingery advises, although I don't go so far as to sift mine out of gravel pit sand anymore. When I was doing that, in order to get fine enough sand, I was sifting through noseeum mesh and throwing away about 90% of the sand I was getting, because it was too coarse. (Note: you want silica sand. Sandbox sand is pulverized limestone, which when the hot metal hits it, will explode. This is a Bad Thing. Use silica sand.)

After a while of using the gravel pit sand, I was frustrated with the quality of the castings. My brother found a supply place in Denver, "United Western Supply Companies (4401 E. 46th Ave, Denver CO 80216-3261) which sells 100 mesh sand and bentonite. They've recommended using a mix of 3% bentonite, 3% water. The sand is incredibly fine and my mixes have excellent bonding, albeit at higher clay and water percentages than they've recommended. The casting quality is good enough that you can see details like scotch tape I've put on molds to cover holes, and recognize it as scotch tape because of the serrated ends. I store my sand in a big Rubbermaid container to keep it from getting soaked by rain, although some water does still get in. Sand which is too wet sizzles a lot and gives a more porous surface to the aluminum. I mixed the sand and clay extensively by pouring them from one container to another and sticking blender blades held in a drill into the mass, before adding any water. I then worked the sand extensively with a spade and hand trowel, using the same sort of motion that you use to spread butter, to mash and shear the sand. That seemed to mix it the best. This takes a long time and a lot of energy.

I advise that you use cast aluminum equipment for any metal that will come in contact with the sand. Steel, even stainless steel, will rust terribly because the combination of water and clay adheres to the surface of the metal and rips particles off.

Everything I've read and everyone I've talked to, convince me that I need to move to Perma-bond oil sand as soon as possible. It is supposed to be vastly superior in its ability to hold detail, the water balance is not critical, and the burnt sand after casting seems to be much easier to reuse. I throw away most of the burned sand and a lot of the completely dried-out sand that sticks to my castings when I'm cleaning them up; for a large casting I dispose of a lot of sand. I mixed about 120 lbs of sand originally; I'm now down to maybe 60 lbs.

You can clean off the castings using running water; that seems to do the best job of getting rid of the sand. You might also brush in crevices and tight corners with a toothbrush or a brass bristlebrush to remove any adhering sand.

Questions or comments: email me!

This page written by John Bump on 12/15/00, last modified 12/15/00.

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