Concrete is becoming a popular choice for countertops because of its versatility and durability. It is also adaptable to different finishes and can be made to look like many different materials--including marble. This is a major advantage because natural marble colours are somewhat limited. With concrete, you can create virtually any colour you want but still have that marble look. It is a challenging project so if you are not handy, hire a professional. If you are experienced with household projects, the following steps should help you create a "marble" countertop.
Determine if the concrete has been sealed. Place a couple of drops of water on the concrete and let them sit. If they are still beads of water after five to 10 minutes, the concrete is sealed. If the water disappears by soaking into the concrete, it is not sealed. Seal the concrete using a concrete-sealing product that can be purchased at a home-improvement store.
Determine which colours you want to use for your "marble" countertop. Select the appropriate paint colours. Purchase a base-coat colour that is lighter than the top coat.
Clean the countertop using a mild dish detergent and sponge. Rinse it off with clean water so there is no soap residue remaining. Let the concrete dry for 24 hours before continuing.
Put on the primer/base coat. This paint should be a similar colour palate as the base coat but in a lighter shade (for example, light blue primer and blue base coat). Allow it to dry, and apply a second coat for full coverage.
Put on the base coat. Be sure it is dry before continuing to the next step. Add a second coat for full coverage.
Mix one-part base coat paint with four-parts acrylic glaze in a large bucket. This acrylic mix can be either lighter or darker than the base coat. This will be the topcoat of the countertop and will give the marble its detail. Use small artist brushes in different sizes and paint lines onto the concrete surface. Make swirls, circles, thick and thin lines across the material. This will create the marble "veins" that give the marble its character. Have the lines flow in the same direction. Use different materials to paint the veins to create a random pattern. Feathers, rags and paper are common options.
Apply a clear gloss varnish coat and allow it to dry. Follow this by applying a satin varnish coat. This will give you the marble finish you are looking for and will protect the countertop. Allow it to dry before using the countertop.