The green sand mixture all foundries use is sand, bentonite and water.

Sand can be found at most masonry supply or home improvement stores. A grain or grit size between 100 and 200 will provide very fine detail, 120 grit is used on all castings on this web site. Ask for a fine sand when looking

Bentonite is used as a patching compound by well drillers, additive for farm feed, to patch dry lake beds and hundreds of other uses. Bentonite can be purchased at pump supply, well drilling supply or some farm supply stores. You can even buy it in a health food store in powdered form, yes, you can eat it!

100lbs. sand mixed with 1 gallon of water, then slowly add 12lbs. bentonite and store in a sealed container or properly covered with a tarp or plastic sheet.


Fine sand, bentonite and water.

Dump sand on clean surface.

Spread sand.

Add water.

Mix with shovel and/or hands.

Thoroughly mix sand and water.


Then add bentonite.


Mix in bentonite thoroughly with shovel.

Stomp sand flat and fluff with shovel. Repeat several times. This mulling action covers each sand molecule with clay.


Store sand in a container  or cover with plastic to retain moisture. If the sand dries out, it must be remulled.  Using riddles (sieves) is enough mulling to keep the sand ready for use.