Home made casting sand

The simplest foundry process to use is sand casting foundry. Of course, not just any type of sand should be used.

Casting sands are a mixture of sand (silica) with a binder. This binder can be natural or chemical. The binder is there to hold the mold to the shape of the part until the solidification of the metal, but thereafter the mold must be easily destroyed to extract the part.

In homemade use, the most common is green sand (sand + clay + water) but there are also sands whose binder is oil.

It is also possible to use soda silicate as a binder, in this case the binder is chemical and the hardening of the mold or the core is done by gassing the sand/silicate mixture with CO2. This last technique is very useful for cores but, of course, can be used for the complete mould.

The recipes that are given in this article are recipes that I have tested until bronze casting.

Green sand

Green sand is a sand that takes shape without chemicals and is used directly for casting metal, it is possible to buy it in the specialized trade, but it is much more interesting to make it yourself with ingredients found in DIY superstores.
The cost of this type of sand is ridiculous but it does not allow to make very complex parts and with too thin walls.
For casting, the mold remains at room temperature, which again limits the parts thickness.

Fine sand, I use sand with grains of 0.5mm

Bentonite, it is a clay which is used, among other things, as litter for cats...
It must be crushed (coffee grinder) and sieved.

And of course water.
My recipe:
8 parts of fine sand
2 parts bentonite
Just enough water to hold the sand together.

I also add a bit of powdered charcoal as the color change helps ensure the mixture is good, this should remain a negligible percentage.

A small sprayer is perfect for adding water gradually
Make the mix dry, then add the water in the form of a mist, then mix well and test the hold, add a little water at a time so as not to have too wet sand.

Regularly test the holding of the sand by squeezing it in the hand, the sand must hold without crumbling and the hand must remain almost dry.

If the sand does not hold together, water must be added.
If the sand sticks in the but, it is too wet and will stick to the model when casting.
When you judge that your sand is ready, you have to do a last test by breaking the clod that you have just squeezed in your hand. The clod must break frankly without bursting.

If, despite adding water, your sand does not hold together enough, you must add a little clay to bind the sand better.

The optimal dosages are to be tested because they vary according to your clay and the grain size of the sand. The finer the sand, the more clay you will need to add.
Here, you now have a batch of green sand, it will have to be kept if possible in a sealed box so that it better retains its humidity. Before each use, it is advisable to redo the resistance and breakage tests because it will be necessary to adjust the humidity before starting the mold making.

After casting, the green sand can be reused, it is necessary to add a little water and possibly clay. It is best not to mix new sand with recycled sand.
See more
A Youtube channel with lots of top casting, not to be missed
La fonderie
Casting sand, many interesting things. In french.
See more
Youtube chanel with many diy castings
La fonderie
Casting sands. French

Oil sand

Oil sand is a variant of green sand where oil is used as a binder. Anglo-Saxons know it as petrobond. Just like green sand, it is possible to find it in specialist shops, but it is relatively expensive.
After some research on the internet and some tests, I found a composition that works very well with bronze, and as usual, all the ingredients are easily found in DIY stores.

Grout for tiling, you must use dry grout in fine powder

Oil, 2-stroke engine oil is perfect because it is designed for high temperatures

100 parts by mass of powder
6 parts by mass of oil
As with green sand, the oil and grouting powder must be well mixed. This mixture takes a very long time to make correctly. Use a spatula to rub the oil well into the powder.

The mixture will be finished when it is perfectly homogeneous and without clogs.

As with green sand, a test must be made by squeezing a handful of sand and breaking the clod obtained.
Compared to green sand, oil sand is finer because the grain size of the grouting powder is much finer than sand. So this sand will make it possible to make molds with finer details.

It is the oil that holds the sand together, so there is no evaporation over time, so this sand keeps better than green sand.

When pouring, the oil will burn, which gives off a lot of smoke and the mold may also catch fire, this is normal.

After casting, the sand near the part has burned and is therefore no longer usable, on the other hand the sand whose oil has not burned can be used again, but it is always better not to mix with new sand .
See more
A Youtube channel with lots of top casting, not to be missed.
La fonderie
Casting sand, many interesting things. In french.
See more
Youtube chanel with many diy castings
La fonderie
Casting sands. French.
Made with OpenElement
Last update
Technical hobbies
Carnets JLS
Top page