Surface sealers for exterior surfaces should be acrylic to allow moisture seeping from the ground to escape. Acrylics are UV-stable. For outdoor use, solvent-based acrylics generally perform better than water-based acrylics.
For interior concrete slabs, three types of sealers are commonly used:
Acrylics are UV-stable, inexpensive, and easy to apply or reapply, when necessary. But they have the softest surface of the three and require the most maintenance. Solvent-based acrylic sealers provide a wet look that greatly enhances the appearance of colored finishes but are softer than water-based products and release noxious fumes.
A typical indoor application consists of one coat of solvent-based acrylic followed by a topcoat application of water-based acrylic. Floor maintenance can be performed with additional applications of water-based acrylic sealers or waxes.
Epoxy sealers are much harder than acrylics. Water-based epoxies bond well to concrete and provide a clear finish, but they are nonporous and do not allow trapped moisture to escape. Epoxies are probably the best choice for concrete countertops and food-preparation areas. They are not UV-resistant, and reapplication involves more elaborate preparation than for acrylics.
Urethane sealers, though the most costly, provide the most abrasive-resistant finish. However, they don’t bond well to concrete, so they must be applied over water-based epoxy applications. They are not UV-stable, and reapplication is expensive.