Concrete has been used in construction for thousands of years, with its earliest known uses for floors, houses, and cisterns in Syria as early as 6500 BC. However, over the last few centuries, the materials used to make concrete have significantly evolved. In 1824, a British bricklayer by the name of Joseph Aspdin evolved the process, creating “Portland Cement." In its modern form, concrete has become one of the most common building materials globally.
Concrete can be left rough or can have a finished look with a skimcoat applied, creating a smooth surface. It can be left uncoated, but should be painted in order to protect it from weathering and to improve its durability. However, when removing paint from concrete, it’s important to follow the proper steps to ensure the integrity of the concrete remains unchanged.
When removing paint from concrete, it must conform to the proper ICRI (International Concrete Repair Institute) CSP (Concrete Surface Profile) Standards of Roughness. This system is a vital industry standard to make sure the proper texture is achieved for successful bonding of coatings.
Below are the most common methods for removing paint from concrete:
Pressure Washing/Water-Jetting/Hydrodemolition
This method uses high-pressure water to blast away paint from the concrete. It’s best used for already loose or peeling paint in large areas. Pressure washing is a good solution for removing paints that are not embedded in the concrete, such as latex paints. However, paints that have become absorbed into the concrete (like spray paints) are unable to be removed via pressure washing, as it has already penetrated into the surface. Additionally, it can be harder to remove older paints, as the longer it has been on the concrete, the further it has penetrated into the surface.
For smaller paint removal jobs, pressure washing can be a cost-effective solution. Requiring less equipment and less training than other surface preparation methods, pressure washing can be a quick and effective way to remove paint from concrete. However, since it involves blasting with water, runoff has to be handled responsibly, as it can contain contaminants such as dirt, grease, oil, and chemicals.
Blasting with any sort of water is also a weather-dependent process. Cold weather can damage the pressure washer, hoses, and nozzles, and make the cleaning less effective. When blasting with water in the cold, moisture can cause surface cracking if it does not evaporate prior to the freeze.
Further, pressure washing can degrade concrete surfaces over time. Concrete is porous and can absorb water. Water blasting typically drives water into the concrete, leading to further surface cracking and failures. Moisturizer corrodes rebar which weakens the concrete's structural support.
Chemical Stripping
This method involves the application of a chemical solution to soften and dissolve the cured surface paint. Strippers are applied wet, bonding to the paint particles during the curing process. Once dry, it is removed, either in sheets or manually scraped off, taking the old paint with it. For small projects, this can be an effective and affordable option, as it requires minimal tools and equipment.
While chemical stripping doesn’t require many tools, in cases involving multiple layers of paint, the strippers must be reapplied several times to remove all the layers. This can prolong the time it takes to remove paint from the surface. Additionally, a washing treatment is required to get the concrete back to its original pH level after using chemical strippers, especially before a new coating is applied.
If not done correctly, chemical stripping can damage concrete. The stripper can get stuck in the cracks and crevices of concrete, preventing proper adhesion of new coatings. Further, certain chemical strippers may be too harsh for certain types of concrete, ultimately weakening the surface.
Conventional Blasting
Conventional abrasive blasting uses abrasive materials such as sand, coal slag, and garnet. This method is effective in removing multiple layers of paint from concrete, including stubborn paints that chemical stripping and pressure washing may struggle to remove.
However, there are still several considerations to make when using this method to remove paint from concrete. First, many ordinary abrasives have high rebound. When doing spot blasting (for example during graffiti removal) areas nearby are often damaged as the abrasive ricochets.
Additionally, the high-impact forces from conventional blasting can cause microfissures, which are tiny cracks in the surface of the concrete. Over time, these microfissures can grow, compromising the strength and integrity of the concrete.
Sponge Blasting
Sponge Blasting is the quickest and most effective way to remove paint from concrete. Due to its low-dust, low-rebound capabilities, it greatly reduces the risk of damage to the surface. While conventional abrasives can cause microfissures, blasting with Sponge Media can remove paint and prepare the surface to the proper ICRI roughness standards, without compromising the integrity of the concrete.
Sponge Media has the ability to get into the cracks and crevices of the concrete, leaving no paint behind in these hard-to-reach areas. This allows for better adhesion of new coatings to the surface.
Further, Sponge Media can be a more cost-effective option than other abrasives. Due to its recyclability, the amount of waste generated is significantly reduced. Not only does this save on waste disposal costs, but it also makes blasting with Sponge Media a more sustainable option. This lower project cost is widely seen on larger job sites.