If the weight of the finished stone is a consideration, the addition of perlite, pumice and peatmoss into a concrete mix reduces weight.
You can also add a styrofoam core without compromising the strength and durability of the stone. The procedure is simple.
- Size a 1/2" sheet of styrofoam to fit inside mold,
leaving a minimum 1" between inner wall of mold and
circumference of styrofoam.
- Wrap styrofoam with a sheet of nylon fiber or wire mesh.
This will help strengthen the finished stone.
- Fill mold with approximately 1/2" - 3/4" of
concrete; tap lightly to remove air bubbles. Place styrofoam
on top of concrete, then pour additional concrete to cover
styrofoam. Fill to top, shake lightly to level concrete.
- To prevent styrofoam from floating to the surface, cover
concrete with a sheet of plastic, then place a brick or
stone in the middle of the mold. This will hold the foam
in place.
 Place styrofoam on top of concrete |
 Pour additional concrete to cover styrofoam |
 Fill concrete to top of mold |