Concrete is vulnerable to chemical attacks and staining because the surface of concrete is rather porous. Liquids and acidic materials can easily seep into the surface of concrete and compromise the integrity of the concrete. Sealants are applied to concrete surfaces to keep them from prematurely deteriorating. A properly applied sealant will make the surface of concrete non-porous and generally make it last for much longer than it would without the protection.
There remain several different types of concrete sealants on the market. Some sealants leave a protective coating on the surface of concrete while others penetrate the concrete to form a protective barrier preventing other materials from penetrating the concrete. Some sealants are water-based while others are oil-based. Wax, acrylics, epoxies and urethanes are topical sealants while densifiers like sodium silicates and repellants like silanes are penetrating sealants.
According to Concrete Network, all concrete sealants, regardless of type, are designed to extend the lifespan of a concrete surface. Both urethanes and epoxies create a stain-resistant surface when they are applied to concrete. Penetrating sealants and urethanes are both heat-resistant materials that create a scratch-resistant surface once applied to concrete. Urethanes and epoxies both leave the surface of concrete with a glossy finish.
Penetrating sealants and waxes will not provide a stain-resistant surface once applied to concrete. Epoxies are one of the only types of concrete sealants that will degrade in the presence of ultraviolet light. Wax sealants have to be applied much more often than other types of sealants. Epoxies create much harder surfaces than other types of sealants. While epoxy may produce a glossy finish similar to urethanes, the concrete will have a signature tint to it after the application of the epoxy.
Most sealants need to be applied quickly to avoid unevenness because they can dry very quickly. Some sealants like urethane are almost always applied over a primer. They are applied over a coating of epoxy to enhance the durability and strength of a concrete surface. While several sealants are used in tandem on a concrete surface, repellant sealants are most often used alone or with a wax.