Color Differences in Sealed Surface

Poorly mixed sealer covers the light areas of this driveway while the dark
areas are covered by the full-strength product.

Question:
This driveway was integrally colored and has a very light brush finish. The concrete was all the same color before sealing, but dramatic color differences occurred after sealing (see photo). The whole driveway was sealed with one coat of a water-based acrylic sealer. The sealer is in good condition with no failures. What caused the light and dark color differences, and how do I make the whole driveway uniform again?

Answer:
I found this situation a bit perplexing at first, and had to do some digging to figure out what happened. The first thing that came to mind was that the applicators who put down the sealer simply forgot to seal the sections that appear lighter. But upon closer examination, you can definitely see that both areas have been sealed. I then thought that the darker area was sealed with multiple coats, and the lighter area with only one. That idea was shot down when multiple parties confirmed that the entire area was sealed with only one coat of sealer.

The break came when one of the applicators stated that three 5-gallon pails of sealer were used on the driveway. Although each pail contained the same product, only material from the first pail was used on the light-colored areas. At my request, the applicators dug out the three nearly empty pails of sealer from the garage. A 1/4-inch-thick layer of resin remained at the bottom of the first pail, indicating that it wasn’t thoroughly mixed prior to application. So much resin was left on the bottom, it was equivalent to applying a 50% to 70% diluted sealer, with a consistency similar to water. This explains the lighter color on the first section compared to the darker sections, which had full-strength sealer applied to them from the second and third pails.

Over time, water-based sealers can separate. Always stir the sealer prior to application to make sure all the resin is in solution. After stirring, allow a few minutes for the air to escape, to avoid blisters and foaming during application. Fortunately, the fix in this case is easy. A second, very light application of sealer (properly mixed, of course) over the lighter areas should bring those areas into uniformity with the darker sections.