machine#construction: casting#techniques: greensand


Green sand consist of sand, clay and water. The sand is generally silica sand. Use 80-100 mesh sand in the mixture. Bentonite is used as the clay because it is hygrophilic, that is, it attracts water. The clay can be sodium bentonite (western bentonite), or calcium bentonite (southern bentonite). You can get bentonite at a farm supply store, or by picking out all the not-gray bits from standard kitty litter. The following mixture for green sand can be scaled to any size batch you need:

100 lbs. silica sand
6 lbs. bentonite
as required water

Water should be added until the mixture will hold its shape when squeezed in your hand. The amount of bentonite can be adjusted to suit your needs.

Greensand Casting  

Although there are hundreds of other webpages out there about sand casting, this page should contain at least a brief overview of the green sand process. Links specific to Petrobond and oil-bonded sand should go under petrobond.


  • More easily reused, mulled and remixed. Does not get burnt.
  • No smoke, no fire, no toxics (other than silica dust)
  • when you are done with it, you can spread it on your garden.
  • cheaper
  • made of commonly available materials (clay, sand)


  • Coarser Finish [But still not all that coarse]
  • It contains water which means Steam, which means venting is more of an issue than with other casting techniques. It also means that you need coarser sand. Finer sand probably would not work as well.
  • microwave core drying
    • faster than oven drying
    • can use a wooden core box
    • i've used regular bentonite greensand as the core starting material
    • just make sure there are no bits of metal in the sand!

Many years back while on tour of a foundry, I saw them using what I
believe they called a "Slinger". This was basically an impeller wheel
on a housing similar to a body grinder. The wheel spun and threw sand
at a pattern in the mold box. It was feed from a vertical hopper and
packed the sand in a very dense manner. It seems they were ready to
pour in just a few minutes. Any one know more about this process? One
guy seem to crank out about 25 of these in less than an hour. We went
to lunch and left the foundry that afternoon with 50 of our castings.
It sure was quick. *1



A sandcasting primer

*1 John Ocala

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