How to Make Stiff-Mix Countertops

Lay the countertop form on a plastic-covered work surface, with the open end of the form up to allow for filling. Make sure the surface is level using a carpenter’s level, to ensure that the counter slab cures level as well.

Mix a small batch of the GFRC face mix for spraying onto the form. Use a bucket to mix the concrete in, along with a drill equipped with a grout mixer. Add enough water to the mix to create concrete slurry with the consistency of a thin pancake batter.

Pour the slurry into a texture spray hopper. Turn on the hopper’s air compressor, and then hold the end of the sprayer 5 inches from the form, pointed directly at the center. Press the trigger of the sprayer to begin spraying the thin concrete over the form’s interior. Cover the interior, including walls, with a layer of the face mix one-eighth-inch thick. Give the mix an hour or two to begin firming before adding the stiffer core concrete.

Cut a piece of steel mesh with tinsnips to fit the interior of the countertop. Use a tape measure to measure the interior space and then subtract an inch from each measurement to provide a space of half an inch on all sides of the mesh when encased in the concrete. The space will keep the mesh from rusting due to exposure to moisture. Wash off the mesh with a piece of steel wool dipped in acetone.

Use a larger bucket or a wheelbarrow to mix the GFRC backer mix. The backer mix will form the rest of your counter slab. Add water slowly to the mix, bringing it up to the consistency of a thick mud. Put on rubber gloves and test the consistency by forming a ball with the concrete. If it just remains together when formed, then it’s ready for use.

Keep the gloves on and press the backer mix into the form over the layer of face mix by hand. Begin at the corners and fill the form halfway to the top with the concrete.

Lay the steel mesh over the concrete, centering the sheet in the form with a gap of half an inch between the mesh edges and the counter's edges.

Finish filling the form with the backer mix, pressing it through the mesh to meet the layer beneath in order to incorporate the mesh fully within the slab. Smooth out the backer mix by hand along the top of the form, and then run a wood screed along the form rim to level the concrete out. Wait two weeks for the concrete to cure before removing the form to reveal the counter.