Concrete is an inexpensive and durable material for countertops, but does not make an ideal surface for food preparation, as it is easily stained and can be etched by exposure to acidic juices and foods. As a result, concrete countertops are almost always sealed to provide an impermeable and stain-repellent surface. Concrete countertop sealers can be separated into penetrating sealers, which alter the surface of the concrete itself, and topical sealers, which form a protective layer on top of the concrete's surface.
Penetrating sealants tend to be resistant to most forms of damage and wear, but offer limited resistance to staining and acid etching. The more effective types of topical sealants form an effective barrier against stains and acid etching. Most of these are, however, vulnerable to scratching or scorching and cannot be applied to concrete that has been polished to a high degree of smoothness.
Most concrete countertop sealers are based on concrete floor sealers, which are formulated with different patterns of wear and damage in mind. Penetrating sealers provide a high degree of resistance against scuffing and scratching, and repel most liquids effectively. They work by hardening the surface of the concrete through a chemical reaction that provides a much tougher and more durable surface than unsealed concrete. Lithium silicate sealers can provide a limited amount of protection against staining, but more common and less expensive formulations — such as sodium silicate — absorb stains almost as easily as unsealed concrete. Penetrating sealers are best used on countertops that are not likely to see a great deal of food preparation, or on concrete that has been polished to a degree which prohibits the use of topical sealers.
The most common concrete countertop sealers are topical sealers that do not penetrate the surface of the concrete. One of the least expensive and most popular sealers is wax, which is generally close in composition to pure beeswax. Concrete wax serves as a sacrificial sealer, which provides good stain resistance and an attractive sheen, so long as it is regularly reapplied as it is worn and scratched away. The vulnerability of wax to scratching and heat damage makes it a problematic sealer for kitchen countertops, although it is one of the few topical sealers that can be applied on top of a penetrating sealer.
Acrylic sealers are popular penetrating sealers for concrete floors, and their low cost and ease of application make them a common choice for sealing concrete countertops. Due to the less porous nature of countertop-grade concrete, however, acrylic sealers act as topical rather than penetrating sealers for countertops. They are less prone to heat damage than wax, but they are also easily scratched. They provide good stain resistance as long as the protective coating remains intact.
The most effective concrete countertop sealers are epoxy sealers and urethanes. These form a thick, durable layer on top of a countertop that is resistant to both damage and staining. They also tend to be considerably more expensive than most other sealers, and many epoxies can be difficult to apply and repair. Such products tend to give the appearance of a thick, plastic-like coating, which may not be attractive to some homeowners. In terms of performance, however, high-end epoxy and urethane sealers come close to the ideal sealer for countertops.