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.
