Epoxy and urethane sealers are used to protect concrete projects that require exceptional abrasion and chemical resistance, increased service life and high gloss. Because epoxy and urethane sealers are essentially impermeable to water vapor, new concrete should be at least one month old and have a low MVT rate when epoxies or urethanes are applied. Otherwise, moisture in the concrete will cause blistering and bond failure of the coating. Check with your sealer manufacturer for maximum MVT recommendations.
Most urethane sealers do not bond well to concrete and must be used in conjunction with an epoxy primer. It is good practice to always consult with the sealer manufacturer to ensure that all the components of the system specified will perform well together. Furthermore, because surface preparation, application method and coverage rates are all very critical when using epoxies and urethanes, the manufacturer's recommendations should be followed precisely for best results.
Penetrating sealers soak into the concrete surface to a depth of 1/8 inch to increase water repellency and stain resistance on absorbent concrete while remaining breathable so water vapor within the slab can evaporate through the surface. Penetrating sealers provide protection without changing the surface appearance.
During application, penetrating sealers enter the voids and capillary pores at the surface of the concrete. These sealers are usually formulated with silane or siloxane polymers that react with alkaline materials in concrete to form hydrophobic compounds within the surface pore structure. Their primary function is to repel water, salts and chlorides while remaining breathable so water vapor within the slab can evaporate through the surface.
Because penetrating sealers soak in and do not leave a membrane on the surface, they do not provide any appearance benefits (no deepening of color or gloss enhancement) and are not as effective as film forming sealers in preventing chemical attack or staining of the concrete surface. However, no surface film means better durability; a penetrating sealer can last as much as 10 years before requiring re-application. Penetrating sealers are a good choice when no change in appearance is desired or when the concrete will be frequently exposed to water or deicing salts.
The importance of using environmentally friendly building materials, coupled with tightening volatile organic compounds (VOCs) regulations nationwide, has made water-based sealers an increasingly popular option for protecting concrete.
Unlike their solvent-based counterparts, water-based sealers are sensitive to the environment during application and in service. At cool temperatures and/or in high humidity conditions, water will evaporate very slowly from a freshly applied water-based product, resulting in poor film formation. This problem will manifest in the form of a milky white appearance or a weakly bonded, powdery film. Water-based products are also susceptible to in-use performance problems in wet conditions.
Low-VOC sealers based on "exempt" solvent technology are also available and often preferred for sealing exterior concrete in highly regulated areas of the United States and Canada. Exempt solvents, such as acetone and tertiary-butyl acetate, dry very quickly making application of sealers containing these solvents quite tricky, especially in warm temperatures. However, exempt solvent sealers are not sensitive to moisture and humidity like their water-based counterparts and can be used in cold weather conditions.
The use of concrete as a finished product will inevitably continue to increase in the future. Designers, owners and installers of concrete can truly optimize their return on concrete investments by selecting and applying the right protective sealer.
Jennifer Crisman is a product manager with The Euclid Chemical Company. She has 15 years of experience in formulating and marketing concrete sealers, coatings and joint fillers. Crisman is a member of ACI committees 308 Concrete Curing and 310 Decorative Concrete, as well as several ASTM International technical committees. You can reach her at (216) 692-8359 or email@example.com.