You had your stamped patio or driveway sealed, and now there are white, milky or cloudy patches where the rich color used to be. Or maybe the whole surface has a hazy, foggy look. This is one of the most common problems we get called out to look at in the Denver area, and the good news is that it can usually be fixed.
Here is what causes stamped concrete sealer to turn white, how to tell which problem you have, and what can be done about it.
What Is Sealer "Blushing"?
When an acrylic sealer turns white or cloudy, it is often called blushing. The clear film that is supposed to sit on top of the concrete has turned milky, so instead of seeing the color of the concrete through a clear coat, you see a white haze. It can show up as small spots, streaks, patches in low areas, or across the whole surface.
Not every white look is the same problem, though. There are a few different causes, and the fix depends on which one you are dealing with.
Common Causes of White or Cloudy Sealer
1. Moisture trapped under the sealer
This is the most common cause. If water gets trapped between the concrete and the sealer film, the sealer turns white. That can happen when sealer is applied to concrete that was not fully dry, when rain, sprinklers or heavy dew hit the surface before the sealer cured, or when moisture works its way up from underneath the slab. Concrete Decor notes that the concrete should stay completely dry before, during and after the sealer is applied.
2. Sealer applied too thick
More sealer is not better. A heavy coat, or too many coats built up over the years, can trap solvent and moisture inside the film. Concrete Decor describes a job where sealer was applied so thick that it blistered once the sun heated the surface. Thick sealer also tends to puddle in the grout lines and low spots of a stamp pattern, which is often exactly where the white shows up first.
3. Wrong weather when it was applied
Sealer needs the right conditions to cure clear. Applying it when it is too hot, too cold, too humid, or right before a storm can cause it to cure cloudy. Colorado's quick weather changes, like a sunny morning followed by an afternoon thunderstorm, make timing important.
4. Old, worn-out sealer
Acrylic sealer breaks down over time from sun, traffic, freeze-thaw and de-icing salts. As it ages, it can turn chalky, hazy or start to peel. That is one reason we recommend resealing stamped concrete every 2 to 3 years. Read does stamped concrete need to be sealed, and how often for more on the reseal schedule.
5. Mixing incompatible sealers
Putting a different type of sealer over an existing one, such as a water-based product over a solvent-based sealer, can lead to poor bonding, haze or peeling. The general rule is to recoat with the same type that is already on the concrete. We explain the difference in water-based vs. solvent-based acrylic sealers.
6. Hard water or mineral deposits (not actually the sealer)
Sometimes the white is sitting on top of the sealer, not in it. Sprinklers that spray the concrete can leave hard-water deposits, usually along the edges where the concrete meets the lawn or landscaping. Concrete Decor notes these are the lesser of the two problems, and they can often be cleaned off with a mild acid cleaner made for mineral deposits, then rinsed and allowed to dry.
How to Tell Which Problem You Have
- White mostly along the edges by the sprinklers? It may be hard-water deposits on top of the sealer.
- Cloudy patches that showed up right after sealing, especially after rain or on a humid day? Moisture was likely trapped during application.
- White in the grout lines and low spots? Often a sign the sealer went on too thick and puddled.
- Hazy, chalky or peeling all over on older sealer? The sealer is likely worn out and failing.
Can White Sealer Be Fixed?
In many cases, yes, especially with solvent-based acrylic sealers.
Solvent-based sealer can be re-opened. Unlike water-based sealer, solvent-based acrylic can be re-dissolved with a solvent like xylene. Foundation Armor notes that blushing in solvent-based acrylic sealers can be repaired with xylene. The xylene softens the film so it can release trapped moisture and lay back down clear. This is the same step that starts our stamped concrete rejuvenation service, where we use a xylene treatment to open up the old sealer before adding fresh accent color and resealing.
Water-based or badly failed sealer usually has to come off. When a water-based sealer fails, or when the sealer is peeling and breaking down, the old sealer typically needs to be stripped before a new coat goes on. Sealing over a failed coat just traps the problem underneath.
Mineral deposits get cleaned, not stripped. If the white is hard-water buildup on top, a proper cleaning, a rinse and a fresh coat of sealer once it is dry is often enough. Adjusting the sprinklers keeps it from coming back.
Whatever the cause, do not just roll another heavy coat of sealer over the white areas. That usually makes it worse.
How to Prevent It
- Seal only when the concrete is completely dry, with no rain in the forecast.
- Apply thin, even coats instead of one heavy coat.
- Keep sprinklers off the concrete while the sealer cures, and aim them away from it afterward.
- Use the same type of sealer that is already on the concrete.
- Reseal on a regular schedule so the sealer never breaks down completely.
Get Your Stamped Concrete Looking Right Again
We use solvent-based acrylic sealer on all of our decorative sealing, and we see white and cloudy sealer on stamped concrete all the time. If your patio, driveway or pool deck has turned hazy, we will come take a look, figure out the cause and recommend the right fix, whether that is re-opening the sealer, a full stamped concrete rejuvenation, or a clean and reseal.
For more on keeping decorative concrete looking good, read should you seal your concrete driveway in Colorado and how to choose your colors for a stamped concrete project.