A Solvent That Works Wonders
by Steve VandeWater
*Please note that the fix described in this article pertains only to solvent based acrylic sealers. It does not necessarily work with water based acrylic sealers.
Acrylic concrete sealer is something that almost all decorative concrete contractors and their customers have dealt with. Because it is very economical and easy to apply, it is used to coat most stamped concrete. The trouble with acrylic sealer is that it’s not very durable. It weathers and wears off rather quickly, lasting only about two years. In addition, it is prone to dulling, hazing, and whitening, (also referred to as “blushing”).
To understand acrylic sealer problems, we must first realize what the product is. Basically, it is a mixture of two components; solid acrylic particles and liquid. The liquid portion of sealer is called the carrier, because it is the means by which the solid particles are “carried” to the concrete surface. In water based acrylic sealers, the carrier is water. In solvent based acrylic sealers, the carrier can be xylene, acetone, or any number of other strong solvents. The solid acrylic particles are what remain on the concrete surface to form a film after the carrier has evaporated. This film repels moisture and some stains in much the same way as a raincoat protects its wearer. The film not only seals the concrete, but also greatly enhances its color and appearance.
Unfortunately, because customers have seen all the magazine and internet ”glamour shots” of freshly sealed stamped concrete, they expect their concrete to look shiny and new indefinitely. When using acrylic sealer, this is simply not possible without ongoing maintenance. Consider the following scenario:
A contractor gets a call from a homeowner reporting that his 6 month old stamped concrete is getting dull, or that the sealer is gone. The contractor tells the owner that it just needs to be resealed. Another coat of sealer is applied and the concrete looks great…for a few months. Then it gets dull again or even starts to haze and whiten. More sealer is added and it looks good… for a little while. Etc., etc., etc. Trying to fix a sealer issue with more sealer is often a terrible mistake!
The problem with dull stamped concrete is often not that the sealer is gone; it is just worn and abraded to the point that it is no longer transparent. Similar to scuffing a piece of plexiglass with sandpaper, acrylic sealer becomes hazy or even opaque when abraded. The sealer is still there, but it’s not shiny anymore and you can no longer see through it.
Applying more sealer works temporarily, because the fresh sealer introduces a solvent such as xylene (the sealer’s carrier) to the surface. The solvent re-melts the existing dull sealer and allows it to combine with the new sealer and fill in all the tiny scratches. The sealer becomes crystal clear again. So the problem is solved, correct? NO!
Remember the scenario above where the gloss was temporary? The reason the sealer kept hazing in a relatively short time was not that the sealer was gone, or even that it was scuffed. Applying more sealer ultimately created problems because it caused too high a build-up of sealer. You see, moisture in the concrete could not evaporate through the overly-thick coat of sealer, so it caused the sealer to lift and detach from the surface. Similar to bubbles beneath bad automobile window tinting, delaminated sealer appears as white or hazy spots.
But how does moisture get into concrete in the first place, especially if it’s been sealed? It can happen in several ways. Perhaps it seeped in through the control joints or other cracks. More likely, rainwater migrated beneath the slab from the surrounding landscape. No matter how water gets underneath the slab, the concrete’s pores wick moisture up like a sponge. If the moisture can’t evaporate, it causes the sealer to haze as it tries to escape the surface.
If applying additional sealer is wrong, how can you fix dull or whitened sealer? For correcting concrete sealer issues, there are few products that can compare with xylene (also called xylol). As noted above, this strong solvent is the liquid part of many film-forming concrete sealers. It is readily available at any home center, paint store, or hardware store.
By applying a coat of straight xylene, one breaks down or re-melts the coat of sealer that is already on the surface. When the xylene evaporates from the reconstituted sealer, it leaves the acrylic solids crystal clear and shiny like new. And all without adding another layer of solids that would create an unacceptable build-up.
Xylene can be applied in three ways, all of which depend on the antiquing and/or cleaning method used when the concrete was stamped.
If the excess antiquing release was thoroughly removed before the original seal coat was applied*, the best way to fix sealer problems is to fill a pail with xylene, and use a natural-bristle brush (on a broom handle) to scrub the xylene onto the surface. The old sealer will melt, the brush will evenly distribute the solid particles, the xylene will very quickly evaporate, and the sealer will dry crystal clear. *Important!: for more on proper antiquing release removal, click here.
If the excess antiquing release was not thoroughly removed and is not actually embedded in the cement paste (is simply lying atop the concrete but beneath the sealer), then scrubbing with xylene will spread the antiquing color around with the melted sealer and will probably create streaking and brush marks when the sealer re-dries. In this case, the xylene would have been better applied by flooding it onto the surface with an industrial metal pump-up sprayer (available at any contractor’s supply store). If applied heavily enough, the xylene should melt the sealer all the way to the surface of the concrete before it evaporates.
The third method involves applying straight xylene heavily with a paint roller. This can accomplish the same thing as brushing, but without creating potential brush marks.
Applying xylene is a great, inexpensive way to rejuvenate dull or whitened sealer. However, be cautious when using it. The fumes can ignite, and any solvent can be harmful to your health. Be sure to read all warnings and technical data before attempting a repair, and wear all applicable personal protective equipment.