Countertop Molds

Although concrete countertops can be poured onsite, most contractors prefer precasting them in a shop to maintain greater control over temperature and curing conditionsand to keep messy wet concrete out of the homes and businesses of their clients. Precasting also can produce a smooth, flat surface not easily obtainable with hand troweling, says Girard.

Obviously, the final appearance of a countertop will largely depend on the quality and precision of the mold its cast in. You can use a variety of materials to make your mold, as long as they are waterproof or sealed against moisture. Mold-making materials recommended by experienced countertop fabricators include wood, polyurethane foam, metal, and rubber. Rhodes often uses Formica because its smooth and durable.

Buying tips: Factors to consider when choosing mold materials include:

  • Strength and rigidity. The mold must be able to withstand the pressure of fresh concrete without bowing or distorting.

  • Surface texture. Concrete will mirror the surface its cast against, so if a smooth surface requiring minimal hand finishing is desired, use a smooth forming material such as Formica. If you plan to hand trowel the countertop surface (by casting the countertop right side up) or mechanically grind the surface after it hardens, then the texture of the mold wont be as important.

  • Workability. Fabricating a mold especially for complex countertop layouts with curves or odd shapes often requires a lot of cutting and manipulation to get it just right. A material that's not prone to splintering or chipping when cut will be easier to work with and reduce waste.

Next: Casting Table

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