Too Much Sealer Can Cause Cloudy, Hazy, Or Whitened Concrete
by Steve VandeWater
Most decorative concrete is sealed; usually with a film-forming acrylic sealer. But why is this product used to seal stamped concrete? Some may answer “in order to protect it”. But to protect it from what? Weather? Staining? Cracking? Acrylic sealers have a limited ability to help with any of these. They do, however, provide a sacrificial surface that somewhat protects the concrete from wear, but probably the biggest reason they are used is because they greatly enhance the appearance of decorative concrete.
Most people mistakenly think of acrylic concrete sealer as a waterproofer, designed to keep moisture out of their concrete altogether. This is just not so. Instead, acrylic sealer forms a transparent, water resistant film which repels a certain amount of water, reduces some types of stains, and imparts a gloss. The amount of gloss is what most people are concerned about when choosing decorative concrete sealer.
Although customers want their stamped concrete to retain its original lustre forever, it is not possible without ongoing maintenance of the seal coat. Even in the best of conditions, exterior acrylic sealer has a lifespan of only 2 or 3 years. This is partly because acrylics are soft and can abrade easily. As the acrylic sealer abrades, it loses transparency. This may happen within a year after the sealer was applied. Like scuffing a varnished surface with sandpaper, acrylic concrete sealer will turn hazy if scratched. Simple foot traffic or even normal weathering will abrade acrylic sealer. It will at some point become dulled or damaged. Usually, the first suggestion is to re-apply another coat of sealer. This is often the wrong thing to do. Applying more sealer can sometimes cause problems.
In fact, probably the most common mistake when applying acrylic sealer is putting it on too heavy. This is done either by the contractor who originally sealed it, or by the homeowner attempting to maintain his concrete’s appearance. No matter who applies the sealer, it is a mistake to think that if a thin coat of sealer is good, then a thick coat is better. With acrylic sealer, a thin coat protects just as well as a thick coat, but without rendering the surface impervious to rising moisture. Yes, moisture rising out of concrete can cause as many sealer problems as moisture going in.
Because concrete is very porous, almost like a sponge, it absorbs moisture in a number of ways. For example, groundwater can wick into a concrete slab from the sides or from underneath. Rainwater can seep into cracks and crack control joints. Water vapor can be drawn from the atmosphere. In short, concrete will almost always contain some moisture. When the concrete heats up, this moisture wants to rise to the surface and pass through the sealer and into the atmosphere. Thinly applied acrylic sealer allows this to happen. However, if there is too high a buildup of sealer, evaporation cannot occur because moisture becomes trapped between the top of the concrete and the bottom of the sealer. This makes the sealer turn white or cloudy, a phenomenon called “blushing”.
Although resealing atop hazy sealer might make colored concrete look better initially, the problem will soon return and worsen. This is because the solvent in the fresh sealer temporarily breaks down the existing sealer, lets the moisture out, and “melts” the old sealer back onto the surface. Then, when the new sealer dries, the coating is twice as thick as before, and becomes even more impermeable to rising moisture.
To clear up whitened sealer, it is far better to redistribute or “re-melt” the existing acrylic topcoat with an application of xylene (xylol), which is a strong solvent that re-wets acrylic sealer. Applying xylene by sprayer, roller, or brush rejuvenates the existing sealer to its original appearance, leaving it smooth, shiny, and clear without adding to the coating’s overall thickness and contributing to further blushing. For more on using xylene, read “Xylene and Stamped Concrete” by clicking here.
In addition to blushing, over-applied sealer can also lose adhesion, crack, and delaminate. If you look very closely at hazy sealer, often you will find that it has hundreds of tiny cracks or that it is flaky and no longer in direct contact with the slab (it has delaminated but is still attached to the sealer surrounding it). The way light is diffused by these cracks is what makes the sealer appear hazy. In other words, looking through cracked sealer is like trying to see clearly through a severely spider-cracked window. To picture how delamination can make sealer look cloudy, imagine a car with poorly applied aftermarket window tinting film. Bubbles between the film and the window make it look gray and blotchy. Applying xylene as described in the previous paragraph can also repair cracked and delaminated sealer.
So how can you tell if your concrete is still sealed and only needs rejuvenation? If when your dull concrete is viewed at an angle the surface has some sheen, it probably still contains sealer. If the surface is completely dull with no sheen at all, then you may in fact need to reseal. Another test is to thoroughly clean the concrete and allow it to dry. If you then place a drop of water on it and the concrete immediately darkens, the sealer is probably gone. If it beads, even for a few seconds, there is probably still sealer present and the concrete may not need to be resealed.
If you determine that your concrete does in fact need to be resealed, be sure follow the manufacturer’s directions to a “T”. Apply the sealer when weather and temperatures are optimum, as written in the product’s instructions. Absolutely wait a MINIMUM of 24 dry hours between washing and resealing or your acrylic concrete sealer is likely to blush.