Many surface-protection options are available to prevent water from entering concrete. Waterproofing coatings or membranes can provide a complete barrier to water, but their impermeability can be a drawback because they can trap within the concrete water that would otherwise evaporate. Another option is to apply a sealer, or clear water repellent. Although they do not render the concrete impermeable, sealers resist water penetration while allowing the concrete to breathe. In addition, they do not alter the appearance of concrete, and they are cheaper than coatings and membranes.
Sealers can be broadly grouped into two general categories: film formers and penetrants. Film-forming sealers, which include acrylics, epoxies, silicones, and stearates, inhibit moisture and chloride penetration by forming a barrier on the concrete surface. Many film formers also impart a gloss or sheen to concrete, so they often are used to highlight colored or exposed-aggregate concrete. Of the products marketed as "penetrating" sealers, few actually penetrate concrete to a measurable depth. Only silanes, siloxanes, silicates, and siliconates can accurately be described as penetrating sealers, and only silanes and siloxanes achieve significant penetration.