How to Make Concrete Countertops Poured in Place
- 1). Use the measuring tape to measure the length of the existing cabinets where the countertop will be placed. Keep track of all measurements by writing them down on a piece of paper, as you will need to refer to them later on.
- 2). Place cement board on top of the cabinets the length and width of the cabinet tops. This will be the underside of the concrete countertops. It will also help protect the cabinets from any moisture in the concrete. Secure the cement board to the cabinets with screws.
- 3). Cut the 2-inch by 4-inch wood studs the length of the cabinet sides. Secure them to the sides of the cabinet with wood screws. They will support the melamine planks that are the sides of the countertop's formwork. You will not need any formwork for the sides of the countertop that are up against an existing wall.
- 4). Cut the melamine planks the same length you cut the 2-inch by 4-inch wood studs. Secure the planks to the 2-inch by 4-inch wood studs with screws that are long enough to pass through the planks and the wood stud and into the cabinet. This will ensure the side formwork will not bulge when the concrete is poured inside of it.
- 5). Level the melamine planks with a level the height you want the top of the countertop to be from the finished floor. Typically, countertops in kitchens are 36 inches above the finished floor. If you are going to be installing a bar-height countertop, then you will want to install it 42 inches above the finished floor.
- 6). Take a measurement of the width and length of the countertop once all the sides of the formwork are installed. Make a note of the measurements on a piece of paper.
- 7). Use the length and width that you measured to size the 1/4-inch rebar to be able to fit inside the formwork. The rebar should be 1/2 inch less then the overall size so that it will not be seen in the finished edges of the countertop
- 8). Arrange the rebar pieces inside the formwork so they make a 6-inch-square grid. Tie the rebar pieces together with the wire ties; by doing this you are creating a solid piece of steel that will resist the tension in the concrete that causes cracks. The rebar needs to be tied together now so that you will be able to hang it from the formwork with more wire ties later on.
- 9). Use the concrete mixer to mix the concrete bags per the manufacturer's instructions. The concrete should look similar to oatmeal or thick peanut butter. It is recommended to use concrete that has a 5000 psi strength, but there are also concrete mixes that are specifically designed for countertops.
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Place the rebar in the center of the formwork height. Place some screws into the sides of the formwork so that you can suspend the rebar with wire ties. You will be able to cut the wire ties during the pour once the concrete is in place to help hold the rebar up. - 11
Pour the concrete into the formwork with buckets so that it is in small amounts that you can control. Push the concrete into the small spaces between the rebar and into the corners so there are no voids in the concrete that will weaken its overall strength. Hammer the sides of the formwork or use a vibrating machine to push the concrete into all the corners and edges. - 12
Place the wood float on top of the concrete, using the formwork as your level guide to level the concrete. With a sawing motion, push the wood float back and forth along the top of the countertop until all the concrete has been evenly distributed. - 13
Trowel the concrete with the steel float to smoothe it out. The more you trowel with the steel float, the smoother the concrete will be. Continue to trowel the concrete until you are satisfied with the finish on top. - 14
Take away the formwork gently after a few days; give the concrete enough time to harden. It is best to try a small area first before pulling out all the formwork to ensure the concrete has hardened. - 15
Buff the concrete with a diamond water polisher to round our the corners. Keep in mind the more you buff the concrete, the more gravel and aggregate inside the concrete will be exposed. If you do not want to see the gravel, then use the diamond polisher very lightly. - 16
Seal the concrete after it has completely hardened. Follow the directions of the sealer, but test a small area first, as some sealers can darken or stain the concrete. A food-safe sealer is required for any countertop that will be in contact with food.
