Why Does My Water-Based Acrylic Sealer Appear Chalky, Dusty or Milky? (Repairing Concrete Sealers)

Soon after your concrete is sealed with a water-based sealer, the concrete surface may appear milky-white. Also, the surface may be covered in a powdery dust. There are several causes to this phenomenon, all resulting from application error:

1. Temperatures below 50°F or high humidity: When a water-based sealer is applied at temperatures below 50°F or in a very humid environment, the water in the formulation does not evaporate as quickly as is necessary in order for the acrylic to form an even film across the surface of the concrete.
   
   Remember that once a water-based sealer is applied to the concrete, there are 3 forces at work: evaporating water, a small amount of evaporating solvents, and a hardening acrylic film (this acrylic film is what protects concrete). The job of the water and the solvents is to make sure that the acrylic maintains its liquid form until it has had time to cover the entire concrete surface. Once the surface is covered, the water and the solvents evaporate into the atmosphere, leaving behind a nice, even acrylic film. At least this is what happens in a successful application.

1. In an example of a failed application, which can happen when the water-based sealer is applied at low temperatures or high humidity, the water does not evaporate as quickly, yet the solvents are evaporating and the acrylic is hardening without any difficulty. Soon, the un-evaporated water will interfere with the hardening of the acrylic, causing it to appear white. The result of such an application error is a random powdery, chalky appearance on the surface of the concrete, or in extreme cases an un-bonded powdered sugar that has formed no film at all.
2. Application prior to rain: If it should happen to rain prior to full film formation, the additional moisture will become trapped in the acrylic as it forms, causing it to appear milky white. This is most likely to occur in the low lying areas, which are the last to evaporate, and collect the most moisture.
3. Premature application: When installing fresh concrete, it's important not to apply a cure & seal prior to the evaporation of all “bleed water” from the concrete surface; approximately one to two hours after final finish. Applying a cure & seal too soon will entrap extra water in the film, causing it to appear milky white.

Correction:

This is not a method for removing the sealer; it is a method intended to correctly re-form the acrylic film. For instruction on how to remove a sealer, please see ChemMasters explanation of our how to strip a sealer.

Necessary supplies: A pressure washer (only necessary if there is a white powder on the concrete surface), a short nap solvent resistant roller, sprayer (optional for xylene application), and a natural bristle broom (if over application of the sealer is severe).

Necessary materials: Xylene (1 gallon for every 300 Sq. ft of work area on the concrete surface).

Step 1

Using the discussion above as a guide, it is important to determine the surface areas where the acrylic has actually bonded to the concrete and formed a film, or where the acrylic is an un-bonded powder. If a white powder is present on the surface of the concrete, then it must be removed using a power washer. Once the surface has been power washed, the concrete should be allowed to dry for 24 hours. If no white powder is present on the concrete surface, please skip Step 1.

Step 2

Xylene¹ should be applied to the problem area at 300 Ft2 /gallon, using a sprayer or a roller, and then allowed to soak until the acrylic is dissolved.

The acrylic will become soft and gummy after approximately 1 to 2 minutes. If over application is substantial, it may be necessary to use a natural bristle broom to gently scrub the acrylic, using care not to disrupt the highlight colors in stamped concrete (highlight colors often appear black, and are designed to accentuate the contours of the stamped concrete, creating an illusion that the concrete is stone). The purpose of this step is to ensure that the xylene has “melted” the surface layer of acrylic, transforming the acrylic from a solid state to a liquid state.

Step 3

A paint roller dampened with xylene should be rolled through the dissolved acrylic to remove the broom pattern (the broom pattern caused by step #2), and leave behind an even film. Also, you should not roll “back-and-forth” with the roller, instead only roll in one direction.