Problem #3: Water-based sealer is white or powdery
Solvent-based sealers dry simply by evaporation of the solvent carrier. The drying process of water-based sealers is more complicated and is significantly affected by the temperature and humidity of the environment during application. Water-based acrylic sealers dry by a process called coalescence where first the water and then the coalescing solvent evaporate and fuse together the acrylic particles to form the sealer film. If the temperature during application is too low or humidity is too high, the coalescing solvent will evaporate before the water does and the sealer will dry white or powdery because the latex particles did not come together before drying.
Some water-based sealers, even after proper application and drying clear, remain susceptible to blushing when exposed to frequent moisture such as around pool decks or in areas where water puddles form. Always read the product literature before applying a sealer to become familiar with its limitations, especially when selecting a water-based product.
Problem #4: Sealer is stained from oil, leaves, tires, fertilizer, etc.
The most common concrete sealers are manufactured with acrylic polymers that do not provide exceptional chemical or stain resistance to the concrete. For more durability and resistance to chemicals and staining, consider an epoxy or urethane coating system, and ensure that the coating is appropriate for exterior use before applying to outdoor concrete.
Problem #5: Concrete is dark and/or blotchy after sealer is applied
Film-forming sealers will darken concrete and leave a glossy shine to some extent, giving the concrete a wet look. The concrete will lighten back to its unsealed color over time as the sealer wears off or is removed.
Because every slab is unique in its color and texture, the color of concrete after sealer application is difficult to predict. The mix design, use of chemical admixtures, finishing techniques and porosity are just a few factors that will affect the concrete surface color. A sealer will deepen the true color of concrete and will highlight all the differences in the surface texture that result from floating and finishing. Sealers also bring out the “grain” in concrete just like a varnish does on wood. If changing the concrete color after sealing is a concern, use a penetrating water repellent sealer or do a small test application of a film-forming sealer to make sure the color change will be acceptable.
Please note that water-based cure and seals are a milky white color as supplied, but will dry clear if applied properly. Water-based sealers do not darken concrete as extensively as solvent-based materials, and the gloss level is lower.
Concrete sealer problems are much easier to prevent than to solve. All of these unfortunate circumstances can be avoided by carefully reading and following the instructions on the sealer technical data page or by contacting the manufacturer to get assistance before applying the product.
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 committees. You can reach her at (216) 692-8359 or firstname.lastname@example.org.