Don safety goggles, gloves and a protective apron. Prepare to pour your cultured concrete in a well-ventilated area. If this is a home-based project, consider performing the pour in an open garage or on a worktable outside.
Fill the air atomized spray gun applicator with polyester resin clear gelcoat and a portion of the hardening catalyst. Evenly spray the mold with the polyester resin clear gelcoat. Allow the gelcoat to harden. It may take anything from five minutes to one hour.
Mix the polyester resin, limestone and the rest of the catalyst hardener together in a bucket. Use as much resin mix as is needed to fill your mold. Molds will vary in size depending on whether the project is a bathtub or a sink. Pour the contents of the bucket evenly over the clear gelcoat on the mold.
Add pigment to the mold while the resin is still wet. Swirl the color to create your own design.
Wait for the mold to dry. The drying process may take one to two hours. The resin will shrink a bit from the mold, making removal of the mold easier later.
Pop the mold out once it has dried. Trim and shine your cultured marble form before installing.