Concrete countertops have become a fashionable alternative to natural stone countertops. Concrete countertops are less expensive than paying £13 or more per square foot for natural stone. While it is not an easy process, do-it-yourselfers can create concrete countertops with preparation and planning in about a week's time.
Preparation begins by having accurate measurements of the countertop length, width and thickness so that moulds can be created. Ideal temperature should be between 50 and 90°F, and the humidity should not be less than 25%. There should be no drastic changes in temperature or humidity while the curing process is going on.
Depending on how complex the design of the countertop is, the moulds can take anywhere from 6 to 12 hours to build. Use melamine to create the edges and quarter-inch thick plywood for the bottom of the mould. It should be a minimum of 1 inch wider than the width of the cabinets. The edges and bottom need to be held tightly together with screws. The bottom of the mould should be attached to the top of the cabinets with silicone adhesive or screws. Knockouts or empty spaces need to be created within the moulds to hold sinks and other fixtures. These can be purchased or homemade with the proper dimensions of the sink and fixtures. The knockouts should also be attached to the moulds by either screws or glue. The final important step to finishing the moulds is to create support grids out of rebar and mesh wire to fit inside each mould.
For an experienced concrete worker, it will take about two hours to mix and pour the concrete into the moulds. The concrete mix used for countertops usually includes bagged concrete, water reducer, polypropylene fibres, varying amounts of concrete stain and water. Make sure that the mix is well blended and the consistency of runny oatmeal. Remember to add the stain according to manufacturer's instructions and to use as little water as possible to reach this consistency to assure proper curing. Once the concrete mix has been poured into the moulds, use the trowel to press the concrete evenly throughout the entire mould. The surface should be level, and the support grids inside the moulds should be completely covered by the concrete when finished. Cover the newly poured concrete with construction plastic and allow the mix to cure in the moulds for a minimum of four days. Detach the melamine sides by removing the screws, and allow the countertops to cure for two more days. During these six days, make sure nothing is placed on the countertops.
To finish the countertops, use a variable-speed grinder with diamond pads to polish the concrete, finish the edges and even out any imperfections. Once the countertop is fully cured, ground and polished, it needs to be sealed and waxed. Concrete sealants and wax can be purchased at home improvement stores. Keep in mind that the countertops will not be completely impervious to stains and will need to be waxed at least once per month. They will also need to be resealed occasionally.