How to Cast a Tabletop in Concrete

Cut two pieces of coated lumber on a table saw to the finished width and the other two pieces to the desired length of the table top. Remember to accommodate the 2-inch thickness of the boards on all sides.

Assemble a square or rectangular frame from your cut lumber; join the boards at right angles and attach the boards at the 90-degree corners with drywall screws. If you are making a rectangular top, keep the shorter width boards inside the longer length boards as you build your frame. Cut the coated plywood sheet large enough to cover one side of the frame and attach it to the frame's edges with more screws.

Turn the frame over so that the solid side is on the bottom. Spread prepared fiber-free concrete evenly in the frame with a straight trowel. Make a layer about 1-inch thick.

Wait 30 minutes and pour prepared reinforced concrete into the frame until only one-quarter inch is left empty. Drag the flat surface of the rubber float over the surface of the concrete in straight lines that overlap as little as possible; this is called floating. Spread another layer of fiber-free concrete over the top, using the remaining quarter-inch of frame space.

Float the surface of the fiber-free concrete just as you did before. Screed the surface of the tabletop, using the frame edges as guides to keep the surface level. Run a finishing trowel over the concrete in straight lines working in a single direction to smooth the concrete surface one last time.

Wait 72 hours. With an assistant, gently turn the frame until the concrete table top loosens and drops out. Sand the entire concrete top using an orbital sander and 100-grit sanding disk.

Rub a tack cloth all over the concrete to pick up sanding dust particles. Apply two coats of masonry sealer to your concrete tabletop, waiting 30 minutes between applications. Let the top dry 24 hours and attach it to the base of your choice with construction adhesive.