Garden ornaments such as decorative wall plaques or small statues that are carved from genuine sandstone can be expensive to buy. A less costly alternative is to make your own sandstone castings using ordinary builder's sand, or even play sand. When the sand is mixed with epoxy resin, which is readily available from craft stores or DIY stores, the resulting material looks very realistic. When using a heavy material such as sand in a mold, make sure the mold is sturdy since a thin latex or silicone mold will not be strong enough to support the weight of the sand and will distort.
Fill the mold with sand to gauge how much sand you need, then transfer the sand to the mixing container.
Mix the epoxy resin with the sand, using a ratio of 1 fl. oz. of epoxy to each cup of sand. Mix gradually, adding the epoxy a little at a time and mixing thoroughly before adding more.
Spoon the sand and epoxy mixture into the mold, adding no more than 1 inch at a time. After adding each inch of sand, tamp the mixture down firmly and then add another layer.
Let the sand and epoxy rest until it is fully cured, then gently take it out of the mold.
The mixed sand and epoxy should resemble brown sugar when it is correctly mixed. If it doesn't clump and stick to itself easily, or it seems too crumbly or dry, you can add a little more epoxy resin.
If the casting does not dry to a hard consistency you could be working in too low a temperature. The ideal temperature is between 70 and 80 degrees F.
Another reason for the casting not to harden properly is if you were working with damp sand. Dry sand out by putting it in the oven set on its coolest setting for 15 minutes.
Apply a release agent, or a thin coating of petroleum jelly, to the inside of the mold to make it easier to remove the sandstone cast.