Throughout the course of its lifetime, concrete suffers many different forms of damage. Although concrete sealers add a protective layer to concrete floors and structures to help maximize their durability and minimize moisture permeability, common issues associated with sealing concrete can be a source of frustration among contractors.
When a concrete sealer doesn’t look or perform as expected, the root cause can usually be traced back to issues like overapplication, application in nonideal conditions or a buildup of multiple coats.
Following are the top five most common concrete sealer issues encountered in the construction field, why they occur, and how contractors can avoid and/or fix them:
Bubbles in concrete sealer usually result from heavy product application. During application of the sealer, outgassing from the concrete surface should be free to quickly move through a thin, wet sealer ﬁlm.
For instance, at a typical coverage rate of 300 square feet per gallon, one coat of an acrylic concrete sealer should be about 5 mils thick when wet. However, when the sealer is dry, it should be only about 2 mils thick. As a point of reference, a sheet of copy paper is 10 mils thick, and a credit card is 120 mils thick.
When the sealer is applied too heavily, the air displaced through the surface can’t escape, and it forms bubbles in the sealer surface. To resolve this, two thin coats should be applied, as opposed to one heavy coat.
In addition, bubbling of a sealer can also occur if applied in hot weather or if the concrete is exposed to direct sunlight. Under these conditions, the sealer will “skin over” and dry on the surface before all the solvent has evaporated. As the solvent attempts to evaporate, pressure buildup will form a bubble on the sealer surface. To avoid this issue, it’s best to apply concrete sealers during the coolest part of the day, when concrete isn’t in direct sunlight.
Solvent-based sealer turns white, peels or flakes
There are two key contributors to “blushing,” or whitening, of a solvent-based concrete sealer.
The ﬁrst is applying the sealer to a wet concrete surface, or to fresh concrete that still contains bleed water. When this occurs, the sealer won’t bond to the concrete surface, but will instead ﬂoat on a trapped ﬁlm of water.
The second cause of sealer blushing is a too-thick application. Heavy coats of sealer, or a buildup of sealer applied many times over the years, will lead to moisture trapped under the sealer and, in time, the sealer losing adhesion to the concrete. When this occurs, the trapped moisture and air under the debonded sealer create a refractive index — in turn making the sealer appear white to the human eye. Eventually, it will peel or ﬂake off the surface.
To avoid this problem, carefully follow the manufacturer’s recommendations regarding coverage rate and the number of suggested coats. In addition, concrete shouldn’t be resealed until the previous coat(s) has worn away or been stripped off. Afterward, use a solvent wash and allow to fully dry.
Water-based sealer is white or powdery
The drying process of water-based sealers is quite complicated and signiﬁcantly affected by the environment’s temperature and humidity during application. Water-based, acrylic sealers dry by a process called “coalescence,” during which the water and then the coalescing solvent evaporate so the acrylic particles fuse together 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. The sealer will dry white or powdery because the latex particles didn’t fuse together before drying. As a best practice, always identify required temperature and humidity conditions for the successful application of a water-based sealer.
To resolve this issue, pressure wash or scrub the concrete to remove any loose debris, before allowing the sealer to completely dry.
Next, perform a solvent wash to bring the remaining product back to the surface and to re-establish the seal. If a solvent wash doesn’t provide the gloss and seal desired, apply a very light coat of sealer after the solvent wash has dried. Concrete cure-and-seal solutions typically last one to three years, so some peeling and flaking should be expected as the product wears away — particularly in areas of high traffic or direct sunlight.
When working with solvents, carefully follow the instructions and safety precautions outlined in the Product Data Sheet and Safety Data Sheet.
Sealer is stained from wear and tear
Over time, it’s not uncommon for concrete sealers to become stained from general wear and tear resulting from repeated or prolonged exposure to oil, tire treads, fertilizer and debris. The most common concrete sealers are manufactured with acrylic polymers that don’t provide exceptional chemical or stain resistance for the concrete.
To maximize durability and stain resistance, use an epoxy or urethane coating system. Be sure the coating is appropriate for exterior use before applying to concrete outdoors.
Concrete is dark and/or blotchy after sealer application
Most acrylic sealers will darken concrete and leave a glossy shine to some extent, giving the concrete a “wet” appearance. Because every slab is unique in its color and texture, the color of the concrete after sealer application can be difﬁcult to predict. A variety of factors — such as mix design, use of chemical admixtures, ﬁnishing techniques or porosity — can have an impact on concrete surface color.
Using a sealer will deepen the true color of concrete and highlight disparities in the surface texture that result from ﬂoating and ﬁnishing. In addition, sealers bring out the “grain” in concrete, just like varnish does on wood. If changing the concrete color after sealing is a concern, it’s recommended to use a penetrating, water-repellent sealer, or to perform a small test application of a ﬁlm-forming sealer to ensure the result is acceptable.