Concrete countertops have exploded onto the home construction scene with various colors and shapes. One complaint, however, is that concrete countertops are heavy, bearing down too much on the cabinet and floor below. However, lightweight concrete countertops are available to those who are concerned about the weight of regular concrete. If you are planning on installing concrete countertops, consider the lightweight alternative.
Attach one sheet of 3/4-inch plywood to your cabinet--more or less, depending on the size and number of cabinets. Use stainless steel screws to attach the plywood to the cabinet tops. The plywood should be exactly the same size as the cabinet tops. If the plywood hangs over, then the concrete will fail to form properly on the overhangs. Temporarily attach 2x4s flush with the top of the cabinet--not the plywood. Attach a 2x6 to the outside of the 2x4, with the bottoms of both boards aligning. These two boards will form the overhang of the concrete countertop. Attach felt paper to the top of the cabinets directly on the plywood. Lay diamond mesh on the felt paper and attach with staples. Mix lightweight concrete in a 5-gallon bucket using a drill and mixing bit. The lightweight concrete can be purchased premixed in 50-pound bags. Add water to the bucket first, then the concrete. Add coloring to the concrete at this point if you so desire. Pour the concrete directly into the countertop form, and gently tap the sides of the form with a hammer to remove air bubbles. You also can use a vibrating sander, placed on the sides of the countertop forms, to remove air bubbles. The removal of the air bubbles is crucial to the lightweight concrete finish. Once the concrete is in place, you can add metal or stones into the upper layer of the concrete. When the concrete has dried, sand the surface to expose the additives and smooth the surface. Add gloss sealer to give the countertop a shine and preserve your work. Remove the forms from the edges of the countertops.