The Concrete Network
Question:

I installed a stamped concrete slab for some homeowners, and they decided they wanted more of the colored release agent removed from the slab after I had already sealed it. They thought it looked too dark. How do I remove the sealer and wash off the release to reduce the intensity of the secondary color?

Answer:

When concrete is stamped using colored antiquing release, the stamps actually push some of the colored powder into surface of the concrete. This process causes the secondary color to be permanently encapsulated in the surface paste of the concrete. So, without writing a Master's thesis and getting into a lot of chemistry, I will keep it simple and tell you that it will be very hard to remove the colored release powder if the slab was stamped properly. The sealer, however, can be removed with a chemical stripper (see Advice on Using Chemical Strippers and The Concrete Network article Best Method for Stripping Sealers).

During that process, you may be able to remove some of the release color. Try attacking the concrete with a stiff-bristle brush, and scrub until you remove some color. This can take a long time, and produce a lot of sweat. If you need to remove more color, try using a very dilute acid (40 parts water to 1 part muriatic acid). Spray down the dilute acid, covering small sections of the slab at a time, then scrub it in with a brush and rinse with soapy water. The acid will actually take up some of the concrete paste, along with some of the color. Test this in an inconspicuous area first to be sure you are getting the results you and the homeowners desire.

Find Concrete Stains, Concrete Dyes, & Concrete Cleaner

Or: