Question: How do I strip sealer from my stamped concrete patio? The installer used color hardener. Will I lose the color off the top when I strip? Will it weaken the concrete? Should I use a liquid stripper or blast it off? Can I stain the concrete after I take off sealer?
I have often said that stripping sealer from stamped concrete is one of the most miserable jobs I have experienced. The job of stripping any coating from concrete is hard enough, but add in the variations and texture of stamped concrete and the job becomes that much more difficult. The questions asked here are fairly common when the reality of having to strip old or failing sealer from concrete presents itself. The most important question, and most common, is whether the sealer should be removed with a chemical process or a mechanical one.
The short answer is almost always to use a chemical. When removing sealers and coatings from stamped concrete, the two most important factors to consider are removing all the sealer and not changing the color or profile of the concrete surface during the process. Most mechanical processes for removing sealers and coatings involve grinding, scraping or blasting, all of which impact the concrete surface and tend to profile or scratch the surface. This is why chemical strippers, which do not impact the concrete surface, are the most common method for removing sealers and coatings from stamped concrete surfaces.
However, a mechanical process may work in certain instances. Soda blasting, a less aggressive mechanical method, has become more widely used in recent years to remove sealers and coatings successfully. Soda blasting utilizes special high-pressure blasting equipment with commercial-grade baking soda granules as the blasting medium. Under high pressure, the baking soda granule is hard enough to break down the coating, but not hard enough to profile the concrete. The downsides are the dusty mess the process creates and the alkalinity of the baking soda dust and its effect on plant life and landscaping.
In regard to the other questions, chemical stripping should have no effect on the color or the concrete surface if the concrete was installed and stamped properly. The active ingredients in chemical strippers are designed to break down plastics and will have no effect on concrete. That being said, depending on the type of colors or pigments used to provide secondary color highlighting and antiquing, the chemical strippers may remove some of those colors. In my experience when powder release was used to antique the concrete, chemical strippers had no effect, but if acrylic tints or post-applied antiquing colors or powders were used, the chemical stripper can remove some of the color.
As a side note, if antiquing color was added to the sealer, as is popular in some regions, the process of stripping the sealer will remove all of its color as well.
Lastly, to answer the question about staining or color-treating the concrete after the sealer is chemically stripped, yes, you can — if the stripping process was performed well and the sealer and stripper residue was completely removed. Cleaning with soap and water (hot water if possible), scrubbing thoroughly, followed by a clean-water rinse is a critical part of the stripping process. Any stripper residue will impact the performance of new sealer being applied to the concrete surface. In many cases I have found that it takes two, maybe three rounds of chemical stripper to get all the sealer off.
It is also important to note that there is a big difference between a chemical stripper and an organic solvent. I often find the two products used interchangeably, and some confusion exists regarding their differences. They are two very different products. I have discussed solvent in a previous Concrete Questions column. To read about this topic, follow this link restoring solvent-based sealers.