Important Considerations: How to Make Concrete Countertops
Traditionally, concrete countertops are fabricated on site, or precast in a concrete shop. Many fabricators enjoy the results when their concrete countertop is poured in a precast mold inside a shop, where all of the environmental conditions can be controlled. They often use specialized formed pre-casting tables.
Alternatively, some fabricators enjoy constructing the countertop on-site. This is because they can create a unique solution that has curved corners or radius edges in one solid continuous piece. This type of process can be performed by do-it-yourself homeowners eager to try their hand at pouring a concrete countertop in place.
The Size and Seams
When the concrete countertop is cast in place in a shop, it has strict size limitations. This is due to the need to ship or handle while transporting it to the site for installation. A 10 square feet piece of a concrete countertop generally weighs approximately 200 pounds. This means that a small 2’ x 5’ section is about all that two strong individuals can lift and position in place. Because of that, it is important to understand proper seam techniques for seaming two pieces together.
Because it is highly dependent on the overall dimension of the countertop, the joints or seams are generally crafted into the design. Using a joint sealer that is 100% silicone is an ideal solution for seams that tightly butt up next to each other. Additionally, the seams can be blended with materials that are identical to granite or marble. This eliminates any aesthetic or design issue.
Before a professional contractor or do-it-yourself homeowner can build the countertop, they need to ensure that the cabinets can handle the weight. Thick 2” concrete countertops generally weigh approximately 12 pounds to 22 pounds for every square foot.
Constructing the molds requires a high level of accuracy to ensure that the template is the exact dimensions required for the countertop. When building the molds off-site, it is important to trace the existing cabinets to create a template. It is crucial to remember that the templates will need to reflect any overhang at the front of the cabinets and possibly the sides.
Usually, the standard countertop overhangs one half inch for regular cabinets, and three quarters of an inch for flush door cabinets. In addition, there should be no overhang where the countertop butts up to the range, refrigerator or other appliance.
The only way to ensure durability in a poured piece of concrete countertop is to use steel mesh along with non-shrinking concrete mix. Usually the mixture is rated at 3000 psi. Once the concrete top has been poured halfway, the mesh can be set in place. This will suspend the mesh approximately halfway between the top and bottom of the countertop.
When learning how to make concrete tops, it is essential to vibrate the poured mixture while still wet, using a concrete vibrator, or sander that can be set to vibration. This will eliminate the buildup of air bubbles and draw the mixture to the corners and edges.