COMMON PROBLEMS WITH EPOXY COATINGS AND 
SIMPLE SOLUTIONS ON HOW TO CORRECT THEM

The most common problem with epoxy coatings is small pinhead size bubbles may appear sporadically over the floor or in honeycomb clusters.  In most cases, the bubbles are caused by air entrapment.  This occurs with outgassing.  Outgassing occurs when the epoxy increases the temperatures of the concrete, causing any trapped air in the concrete to heat up and expands, thus creating bubbles under the epoxy coating. 

Outgassing can be easily avoided by sealing the concrete first with a primer or sealer made especially for epoxy coating such as Benjamin Moore's Moisture Tolerant, emulsified epoxy coating. 

The second common of bubbles is caused by excessive airflow, which causes the epoxy to dry too quickly.  This usually happens with too much air is allowed to flow over the floor through open doorways, from HVAC or other sources.  To prevent this simply turn off your HVAC blowers, if this is possible.  If it is not possible, then try to redirect the airflow away from your newly applied epoxy coating.

Another cause of bubbles is due to excessive heat, usually caused by heaters or applying the epoxy coating during extreme weather.  It is important to avoid high-temperature conditions whenever possible.

Applying the epoxy coating in direct sunlight can also cause air bubbles to form because the heat of the sun will heat up the concrete.  However, this doesn’t mean you have to apply your epoxy coating in the middle of the night.  Applying epoxy coatings in muted sunlight should not cause outgassing.  You can also wait until the sunlight is no longer shining on that area of the floor.

Another cause of bubbles is using too aggressive mixing action, such as a power drill set at a speed of over 600 rpm.  When mixing with a power drill to mix with, make sure you set the speed between 300-500 rpm and use a spiral-mixing blade.  Make sure that you move the mixing blade all around the inside edge of the pail from bottom to top to ensure proper mixing.

Poor rolling will also create bubbles.  When rolling, make sure that you do not use too short or too long of a stroke and that you do not use a foam roller covers, as these have been known to also cause bubbles.  You want to always use a top-quality, lint-free, medium-nap roller sleeve and use smooth, gentle strokes when roll on the epoxy coating.  In addition, consider performing the final back rolling with a spiked plastic roller.

Bubbles in Epoxy Coatings:

If you have bubbles, the only way to repair the damage is to abrade the area thoroughly with medium grit sandpaper and a rotary disc scrubber.  Once you have abrade the area, you need to vacuum/clean off dust, we use a tack rag to make sure we have removed all the debris.  We also wiped the area with xylene or a strong solvent.  Once the area has completely dried, recoat the area.  

For large bubbles, those bigger than a dime, may require hand grinding before sanding and with all bubbles, always feather edge all imperfections.

Note: If you have a moisture problem that is causing the coating to bubble, and there is no moisture barrier beneath the concrete slab, there is no method to eliminate the problem.  It is strongly recommend that you strip all of the coating to bare concrete and then seal the entire area with several coats of an epoxy tolerant moisture primer such as Benjamin Moore M68/69 Moisture Tolerant Epoxy.

Shortage on Coverage:

The majority of manufacturers have strict coverage rates.  Therefore, if the area you want to coat is larger than the published coverage rate, always purchase another kit, or gallon.  Do not try to “Stretch it.”  However, there are times when you have followed all directions and still come up with less than what was specified.  

One reason for shortage could be attributed to low temperatures.  This is because coverage rates of all manufacturers are based upon applying the epoxy coating with temperatures between 70°-75° F.  When the air temperature or surface temperatures are below 70^oF, the epoxy coating will become thicker, making it very difficult to spread.  To help eliminate this problem you can raise the room temperature or the floor surface temperature so that it is between 70^oF-75^oF.  Some experts also recommend that you cut the epoxy with a 5% recommended thinner.  However, we do not recommend this as it will also decrease the "set" time and can cause other more serious problems.

Another cause of shortage is caused by application technique, where the epoxy is applied with not enough pressure to the roller.  For this reason, it is vital to monitor your coverage rate and to adjust how you are applying your coat accordingly.  

After 24-Hour Cure, the Coating is Still Soft:

If after the sufficient amount of curing time has passed, your epoxy coating still has not hardened, or has a tacky feel, the problem more than likely is that no catalyst occurred.  Unfortunately, this happened because the Part B was either not added to the Part A prior to mixing, or the right proportions were not mixed together.  If you go back and count the number of part A's and B's used more than likely you will find the discrepancy.

If the majority of your floor has cured, but you still have tacky or sticky areas, this is caused by insufficient mixing or if part A and B were not mixed according to the manufacturer's instructions.  Tacky areas can also be due if someone took and place the mixing pail upside-down onto a floor surface, so that you can use every drop.  As tempting as this may be to do---DO NOT DO THIS!  When you place the mixing pail upside down and allow all the epoxy mixture to drain out there may be unmixed or unblended resins that are on the sides of the pail that will drip onto the floor. 

If the surface however, is soft and uniformed, this is usually due to application in cold temperatures.  However, in some instances, it is due to an improper ratio of Parts A to B.

For all of these problems, test the problem area to ensure that the epoxy floor sealer/finish is not wet or tacky to the touch.  As long as the sealer/finish is not wet, then it can be top coated.  However, if this does not repair the problem, then the area will have to be shot-blast, cleaned, then recoat according to the manufacturer’s instructions.

Imperfections and Fish Eyes:

Fish eyes are imperfections in the surface of the epoxy coating, which resemble the fish eyes.  Deposits of residual silicone on the surface of the floor cause this type of imperfection.  To avoid this type of imperfection, make sure that you properly prepare the concrete surface with the recommended solvent or stripping agent to remove any silicone contaminants.

Any petroleum-based lubricant as well as any form of oil or grease including that from food products will cause surface problems, which will cause the epoxy coating to improperly bond.  To prevent any problems make sure that you remove all petroleum-based contaminants with an Oil & Grease Emulsifier, followed by a thorough chemical cleaning with caustic, acid, and detergent, test the concrete surface for contamination from an oily substrate by sprinkling with water.  If it beads up, steam clean or torch to bring the contaminant to the surface, and chemically clean again.

The only way to repair fisheyes or other imperfections caused by oil or grease residue is to thoroughly sand the surface of the area, then following the steps, thoroughly clean, the area again, making sure that you remove the silicon, oil or grease.  Before you recoat the area, make sure that you go back over the area with a vacuum or clean the area with a tack rag to ensure that you remove all debris.  Before you recoat your entire floor, only apply one unit at a time to monitor to see if the fish eyes reoccurrence.

Poor Adhesion, Peeling, or Flaking:

Poor adhesion, peeling, and flaking are condition of delamination.  Many times, inadequate cleaning or preparation of the concrete surface prior to applying the epoxy coating causes delaminating. 

Another cause of poor adhesion is excessive moisture, which will cause blisters in the epoxy surface that later peel away.  

Whether the cause was due poor preparation or moisture, the only way to correct poor adhesion is to sand blast the surface, removing all the flaking coating.  Many times, when left alone or ignored, blisters will expand or grow, as the more moisture accumulates underneath the surface of the epoxy.  For this reason, it is important to note that if you are applying 100% solid epoxies, they should only be applied on-grade concrete floors that have a Visqueen moisture barrier or another reputable poly-sheeting barrier beneath them.  In addition, you can use a moisture meter to test for moisture content prior to application.  A simple test that is easy to perform is to tape down a 3 square foot area of 4-6 mil plastic for a minimum of 72 hours, then check underneath the plastic for any accumulation of moisture. 

Inter-coat delamination is another form of poor adhesion.  Applying epoxy coating over a previously applied coating often causes this.  It is important, to always take time to test for compatibility/adhesion if you plan to reapply any coating. 

In addition, if the surface that is to be coated shows any gloss whatsoever, the surface should be abraded using a medium to coarse sandpaper.  Make sure that you remove any dust from the surface with a tack ragged or wipe the surface with a rag and strong such as xylene, prior to the applying the new coating. 

If you have an adhesion problem that is throughout your entire floor, it is best that you shot blast the entire floor to the bare concrete, then following the instructions on the coating product, recoat the floor.  Make sure however, that you correct any problems due to moisture.

If the problem is isolated, then you can key the perimeter with a sharp utility knife, and then remove all of the coating to the bare concrete from inside the key area.  Then repair the area, making sure that you follow the coating instructions as specified.

After 24-Hour of Curing the Finish is Still Dull or Low-Gloss:

A dull finish after more than 24 hours can be due to several reasons.  The most common reason however is from poor ventilation.  When you apply 100% solids epoxy the solvent can become trapped within the coating, causing the finish to dull.  This is why having proper ventilation/air flow is strongly recommended.

The second most common cause of a dull finish is excessive humidity, which is humidity of above 60%.  For this reason, epoxy coating should not be a task performed on rainy days.  It is always better to wait for less humid weather.  To help reduce the amount of humidity in the room, you can operate a dehumidifier or run your air condition.  

Other causes of a dull finish are improper mixing and/or applying the epoxy coating when either the air temperature or surface temperature of the concrete is cold.  It is important to note that excessive humidity that which is above 60% and/or cold temperatures can cause blushing.  This is a dull finish or a very slight "oily" finish over a hardened, cured 100% solids epoxy coating/floor.

If your concrete coating has blush or an oily film, you can scrub the surface using a strong neutral pH detergent or sponge clean using a solvent such as xylene.  If this does not correct the problem, or if the recoat time has elapsed, then you will need to thoroughly sand or grind the concrete flooring, followed by removing the dust with a tack rag before you recoat your flooring.

Lumps, Bumps or Globs in the Surface:

Sometimes no matter how well you sand, rinse, and clean the concrete surface, you will still discover lumps, bumps, or globs in the dried surface.  These lumps, bumps, and globs of often lumps of 100% solids epoxy caused by poor mixing or from using dirty equipment when mixing or applying the epoxy coating.  Lumps can also come from lint from the roller sleeve that you use, especially if you opt to purchase less expensive rollers.  There is nothing wrong with trying to save money, however, it’s always best to purchase quality rollers when apply epoxy.  Another area where you do not want to cut coast is purchasing or using epoxy products that have expired, as they will usually lump.

Another cause of lumping is when part A has been frozen.  If you live in a cold climate area, make sure that part A is completely thawed at 85° F for 72 hours, and then you want to blend it thoroughly before using.

If you have bumps, lumps, or globs in your epoxy coating, to correct these imperfections is to sand or grind out the imperfections and then recoat the areas.

Wrinkles:

Wrinkles are rare; however, they do appear when applying 100% solids epoxy coating.  The main causes of wrinkles are due to excessive thinning.  Excessive thinning is usually caused by solvent added to the coating.  However, wrinkles can appear when the coating is applied too thick, or when it has a soft film surface.  If you need to apply a thick coating to achieve a higher mil thickness in order to fill in spalls, voids, or rough areas, it is strongly suggested that you use little to no solvent thinner.

Another cause of wrinkling is applying the epoxy coating to a cold concrete surface.  This is when the surface temperature is below 50°F.