Common Acrylic Concrete Sealer Problems & How To Prevent and Fix Them
Oil based acrylic sealers (a.k.a. solvent acrylic or wet look sealers) are commonly used on exterior and interior concrete for aesthetic appeal and concrete protection (e.g. resistance to abrasion, dusting, staining, cracking, spalling). While application instructions are typically laid out on product tech data sheets, little to no info is provided on how to determine the cause of a coating problem and rectify the situation. Coating problems can include surface bubbles (aka solvent pop), peeling/flaking, white spots (aka blushing), fading (loss of shine).
SURFACE BUBBLES (AKA SOLVENT POP)
Surface bubbles (aka solvent pop) can occur during the coating application process when solvent is evaporating too quickly from a sealer. Increased temperatures and direct sunlight are known contributors to surface bubbles. Once cured, these bubbles are often fragile and will can crack when you step on or apply pressure to them.
Solvent pop can occur in the first coat, however it’s more common in the second coat especially when the second coat is applied within 24 hours of first coat. Hot temperatures and direct sunlight rapidly release solvent from the first coat which may become trapped under the second coat, resulting in surface bubbles.
Another contributing factor of surface bubbles (often overlooked) is a rapid increase of the concrete temperature. If the air within the concrete (below a fresh coating) is cool and begins to heat up quickly, it will expand and exert pressure on the soft, fresh coating, resulting in surface bubbles.
To significantly reduce the risk of solvent pop and allow your concrete coating to penetrate and bond better, use the following strategies. First, try to apply the oil based acrylic sealer after the concrete has warmed up and the sun is not shining too intensely on the surface. Applying the sealer between 50 to 60F is ideal. This temperature range is often not realistic during warmer months of the year. If you need to apply sealer during hotter conditions, try to limit the temperature to no more than 85F and apply later in the day when the sun is not shining too intensely on the concrete and the concrete and ambient temperature are beginning to cool.
If for some reason you read this information after the fact (you already have bubbles in the coating), there are several steps you can take to rectify the situation. Begin by not crunching all of the surface bubbles if they have cured. This will just remove material from the problem area. Next, if you recently applied the material and it has not had at least 24 hours to off gas solvent, don’t try to fix it or you may end up with more bubbles.
After at least 24 hours, the irregular surface can be re-emulsified with a solvent product such as xylene or Armor Blush Repair. Re-emulsification is simply applying a solvent product that will soften up a solvent acrylic coating and melt it down smooth before it re-cures hard again. Armor Blush Repair for re-emulsification is preferred because it has a combination of fast and slow release solvents which give the applicator more time to apply the product. Xylene will work in most instances but evaporates away faster and is not as user friendly as the Armor Blush Repair.
Additional supplies needed to re-emulsify solvent acrylic coatings include a metal or plastic pvc paint rolling tray, 3/8 to ½ inch nap roller and safety supplies (gloves and goggles). If the surface being repaired has indentations(eg stamped concrete), opting for a ½ inch roller will help penetrate deeper into the low points (valleys).
Prior to re-emulsifying a bubbled, solvent acrylic coating, make sure that the coating has cured for at least 24 hours and that the weather will remain clear for 48 hours following the treatment. If it rains or the surface somehow becomes wet (e.g. sprinklers) prior to 48 hours of curing, the coating could blush (turn white) which is a separate issue. Repairing the coating with Armor Blush Repair or Xylene should be done in conditions similar to the coating application process. Basically, make sure the concrete is dry (and will stay dry for 48 hours), the concrete and ambient temperature have warmed up (50 to 85F), and the sun is not shining intensely on the coating (wait till later in the day when the sun starts to head for the horizon and the concrete begins to cool if in warmer months).
Begin re-emulsification process by filling your paint tray with Armor Blush Repair or Xylene and then wet your nap roller with the solvent in your paint tray. Place the roller on the bubbled acrylic coating and begin to roll back and forth repeatedly. Apply minimum downward pressure to avoid pushing the acrylic off of an area as it softens up. Roll until you see the coating bubbles flatten out and then stop rolling immediately. Excessive rolling/downward pressure can wear away acrylic, leaving a bald spots. Bald spots will not protect the concrete and will have little to no shine. Prior to repairing the entire surface, test a very small area to confirm results. One treatment with your selected solvent should be adequate but the process and be repeated as needed (remember to always test a small area). As previously noted, remember to keep the surface dry for 48 hours after repairing the coating.
BLUSHING (WHITE SPOTS)
Blushing occurs when moisture becomes trapped within your coating or between the concrete and coating which leaves an unpleasant white appearance (blushing can be an isolated issue or more widespread). Frequent causes of blushing include applying solvent acrylic to surfaces that are damp, rain or sprinklers hitting a freshly sealed surface (within 48 hours of application), applying too much acrylic initially or later after years of re-coating (trapped moisture).
If you just cleaned your concrete to apply new sealer, give the surface a couple days to dry. If you are in a hotter/dry climate, 24 hours may be sufficient. Another, often overlooked source of concrete dampness is morning dew. Wait till later in the day to seal concrete to prevent blushing (from morning dew) and solvent pop (surface bubbles).
Watch out for Mother Nature, while not always predictable, it’s a good idea to check your local weather forecast. If you have any doubts about rain, hold off and plan to seal on another day. Also consider that after applying your initial solvent acrylic coating, it’s best to wait 24 hours before applying an optional second coat. If you apply a first coat and the weather changes before you apply the second coat, delay the second coat, let the surface dry again and then apply the second coat. Many people don’t realize that oil based/solvent acrylic sealers will chemically soften an existing, fully cured solvent acrylic coating and bond without any sanding (no true recoat window).
Make sure you remember to shut your irrigation sprinkler system off while sealing with solvent acrylic. Many people have forgotten to do this and it’s frustrating. Fortunately it’s not the end of the world because the surface can be repaired but this mistake will cost you time and a little bit of money.
While applying acrylic to an unsealed surface, it may sound like a good idea to apply one heavy coat, especially if the concrete is very porous and wants to absorb an excessive amount of material. This is a bad idea mainly because most exterior acrylic sealers have a lower solids content to allow moisture vapor to pass through rather than being trapped below the coating. If the surface is very absorbent, apply one even coat and let it dry. Once the first coat dries, it slightly congests the substrate pores to reduce the amount of material needed for the second coat. Even if the surface does not look perfect with one coat, don’t worry, a second light coat will typically even out the appearance for a uniform look. Light coats help retain surface breathability and keep product cost down (less volume).
After years of recoating (usually every 2 to 5 years between coats) the acrylic solids content on your concrete can build up to a level where moisture becomes trapped. The pressure exerted by the trapped moisture can cause the coating to separate from the concrete (delamination). This space between the coating and concrete acts as a reservoir for water often resulting in a white/cloudy appearance (coating failure).
To repair a solvent acrylic coating that has blushed/turned white, start by considering re-emulsification and only strip off old acrylic if this treatment fails. If moisture is only trapped in the coating and not below it, the Armor Blush Repair or Xylene should clear up the coating. Wet your roller with one of these two solvent products and roll repeatedly back and forth for about fifteen to thirty seconds with little downward pressure. These solvent products will melt/soften the acrylic coating (re-emulsify) which will allow moisture to escape and allow the coating to dry clear again in most instances. Continue to monitor the treated acrylic to make sure that it does not turn white again. If the first application does not completely clear up the coating, the process can be repeated (wait 24 hours before repeating process).
If the coating is white after partial delamination from concrete, rolling with Armor Blush Repair or Xylene should soften the coating enough to allow it to penetrate back into the concrete pores and bond again. Results may vary depending upon the quality of the acrylic resin and moisture content within the concrete. If a test area fails to remain clear after numerous treatments with Armor Blush Repair or Xylene, you may need to strip off the coating. Premium strippers from your local hardware store in the paint section in conjunction with a pressure sprayer will help remove problematic coatings.
Coating strippers in gel form will not evaporate away as quickly as a standard low viscosity stripper. Using a stiff bristle brush to work the solvent into the old coating helps loosen it. After working the solvent into the coating, use the high pressure washer to remove material. Hot water pressure washers with a turbojet nozzle are ideal but cold water sprayers with solvent strippers will work. Repeat stripping process as many times as needed to remove the old acrylic from the surface. Wear safety equipment such as goggles, gloves and long sleeve shirt and pants. There are more environmentally friendly strippers but solvent strippers with MEK and Methylene Chloride are the most aggressive. Always run a small test area to confirm results. Some dyes (eg solvent release) below the old coating may be affected by certain strippers.
All acrylic coatings will experience photo degradation over time when exposed to constant sunlight. Depending upon your geographic region (eg Arizona vs Illinois) the degradation can vary. Bright, sunny environments will usually dull a gloss coating quicker than a region with more cloud cover. To reduce acrylic treatments, apply high quality sealers that have better resins such as the Foundation Armor AR350 and AR500. Better resins will increase the product life and will not yellow like low quality resins.
If a coating fades to the point where it needs to be freshened up, use the same procedure for re-emulsification as you would for repairing a coating that has blushed. Roll the surface with Armor Blush Repair or Xylene for about fifteen to thirty seconds with little downward pressure and let it dry for 24 hours before re-evaluating. Retreat as necessary, fading usually requires just one solvent treatment. If any areas are bald from surface abrasion (traffic), apply additional acrylic to maintain surface protection and aesthetic appearance.
PEELING AND FLAKING
Solvent/oil based acrylic sealer peeling and flaking (failure) can result from a number of causes including previous sealers which are incompatible (e.g. water based acrylic, wax, urethanes and epoxy), poor surface preparation prior to application (e.g. not properly cleaned or dried), excessive subsurface moisture (poor drainage or acrylic buildup), failure to maintain a coating and application of low quality product(s).
As mentioned previously, one of the benefits of using solvent acrylic is that in most instances, additional coats can be applied without having to remove/strip the existing solvent acrylic coat. A new coat of solvent acrylic will soften up the existing solvent acrylic coating which allows the new coat to chemically bond (as long as the existing coating is in fair shape, eg not peeling or flaking). This is not the case with other coatings such as epoxy, urethane and water based acrylics. Unlike solvent acrylic coatings, these coatings need to be scuffed/sanded to about 80 grit for additional coatings to bond. Solvent acrylic should only be applied over solvent acrylic to ensure proper bonding. If another kind of sealer was previously applied to the concrete, it should be chemically or mechanically stripped prior to solvent acrylic application.
If concrete is unsealed, ensure that it is clean and dry prior to application of solvent/oil based acrylic sealers. Removing dirt and debris from the concrete pores allows the sealer to penetrate and bond well. High ph cleaners with sodium hydroxide can effectively cut though oil and grease stains in addition to removing dirt and grime. For dirty concrete without excessive oil staining, concentrated concrete cleaners such as the Armor ER100 are an excellent choice. Dawn dish soap and simple green are also options for light concrete cleaning.
After cleaning concrete, rinse it well and give it adequate time to dry before applying solvent/oil based acrylic. These sealers are oil based and need a dry surface for adequate penetration. Oil and water don’t mix so let the concrete dry for a couple days if needed. Once again, watch out for morning dew and apply later in the day (after the sun evaporates the dew and dries the concrete).
If you are applying solvent acrylic to an area exposed to the elements, make sure there is adequate drainage for water runoff. Acrylic coatings are designed to breathe which allows subsurface moisture to pass though. If the sealed area cannot breathe due to standing water, water trapped below the coating can cause excessive pressure resulting in failure of the coating.
Moisture can also become trapped below excessive acrylic buildup. This includes acrylic that is applied too heavy or having applied many normal coats over the course of a long period (eg a decade). If excessive build of acrylic is a problem, you can use premium solvent strippers (available at most hardware stores) in conjunction with a stiff bristle brush and a high pressure washer to remove excess build up. After removing the buildup, new coatings can be applied that will function adequately by breathing.
Applying acrylic requires routine maintenance about every 2 to 5 years on average depending upon the environment. With low traffic and when applied inside, acrylic coatings can easily exceed the average maintenance window. For exterior applications, photo degradation (sun exposure) and surface abrasion will eventually breakdown the solvent acrylic coating with time. Periodically maintaining the coating with fresh coats will help prevent water freeze thaw cycles and contaminate penetration (eg salt or ice melt) below the coating which can cause coating failure. Ice melts will degrade the concrete below the coating at a chemical level while water freeze thaw cycles spall (chip) the concrete though expansion and contraction. Concrete left to the elements for years without retreatment may eventually look as if it was never sealed or worse, damaged.
Product quality is often overlooked in favor of pricing and immediate convenience. A great example would be solvent acrylic sealers offered on the store shelves of most big box stores. Many concrete sealer manufacturers are forced to provide lower quality sealers to larger retailers due to pricing constraints. To keep the product price down, box store concrete sealer manufacturers will often use lower quality resins that yellow, fade and ultimately degrade prematurely causing coating failure.
One example of a company that does not compromise on product quality is Foundation Armor. All of their products including solvent acrylics such as the AR350, AR500, AX25, LV25 and AG Brown Seal use only the highest quality components.