Mixing molding sand (greensand)

Begin by pouring a 50 pound bag of playsand into a large mixing tub.

Playsand is an extreamly fine sand used in children's sandboxes. The finer the sand the smoother the surface of the castings will be. This sand is so fine it almost feels like a powder.

I buy mine from the Home Depot store and in some cases it is packaged with the name "natural sand" instead of "playsand" on the package.

Make sure the sand is moistened slightly (it is usually sold moist already). Have the fireclay ready since it will be added next.

Spread the clay (it is in powder form) over the sand and mix it in thoroughly.

It is good to pour in half the clay, mix it around and then pour in the remainder of the clay and mix thoroughly.

Here's the molding sand fully mixed and ready for use. It's a very simple process. It is best to let it set for an hour before use so the clay can fully absorb the water and bond to the sand better. The sand tends to improve after a few usages since the clay get a further mixing-in.

Specialty molding sands exist with other ingredients mixed in, but that is beyond the scope of this introduction.

Question: How many times can the molding sand be used?
Answer: The molding sand can be reused HUNDREDS of times. After pouring metal into it, the hard clumps of dried sand are simply re-tempered (sprinkled with water to bring it back to the proper moister content) and broken apart. So depending on how often you cast metal it can last for many years. Usually you know the sand needs replacing when it stops sticking together well and falls apart in the molds. This can be a result of the clay bonding being "worn out" or the eventual buildup of the parting compound dusted onto the sand during the mold making process. For more details of various sandmolding processes get yourself a copy of How to cast metal in sand.

Testing the sand

A good test for the sand is to squeeze some in your hand. The sand should compress together firmly and show good detail of your hand. Very little sand should stick to your hand.

If the sand does not squeeze together well and crumbles it is too dry, add more water. If it is "muddy" and sticks to your hands a lot it is too wet, let it dry out some. Give the sand at least an hour after mixing before you test it so the clay can fully absorb the moisture.

The squeezed sand should break apart in large clumps with very little crumbling. The moisture content of the sand should be like a well rung out sponge. I once read it described as being like "brown sugar" but not as sticky, which is a good comparison.

Question: How many molds can I make at a time with 50 pounds of greensand?
Answer: Depending on the size of your patterns (larger patterns fill more space in a flask requiring less sand), this batch of molding sand will fill on average, 2 of the 8" x 8" flasks and one additional smaller flask.

The sand fits conveniently into a 5 U.S. gallon plastic bucket for storage. Keep the sand covered so it stays moist and to keep debris out.