Cleaning and etching concrete is vital for a successful outcome when applying paint coatings to bare concrete. If contaminants are present, a thorough cleaning should be performed prior to etching. Any existing sealers or paint coatings must also be removed beforehand.
Alkaline Base Concrete Cleaner/Degreaser
Alkaline base concrete cleaners/degreasers are commonly used to eliminate petroleum based stains such as oils and grease. These detergent type cleaners are effective because they are able to soften and break down oily deposits. Alkaline concrete cleaners are similar to most cleaning products insofar as they do require scrubbing as part of the cleaning process. This enables the detergent to properly penetrate the stains. Multiple applications may be necessary for stains that have penetrated deeper into the concrete. The oily residue should then be removed by mopping, ragging, or vacuuming.
Using an alkaline concrete cleaner can also neutralize concrete after it has been acid etched, by raising the pH level. A pH close to 7 is ideal for paint application. A pH below 6 or above 9 can damage paint coatings leading to paint failure.
Alkaline concrete cleaners are typically sold as concentrates and can be diluted with water. Always follow product label directions for best results.
Muriatic Acid or Hydrochloric Acid is a highly corrosive acid commonly used for etching concrete. Muriatic Acid is dangerous and must be used with the utmost care. It produces very strong fumes which can cause significant health risks to the user. This acid is usually sold in a 30-40% solution. It should be further diluted into a 10% solution. This can be achieved by mixing 3 parts water to 1 part acid. Slowly add the acid to the water. Never pour water into the acid. Be sure to follow product directions for use. A slightly stronger solution, not to exceed 15% may be necessary for concrete that is very hard and smooth.
Sulfamic Acid is the primary ingredient for many acid base concrete cleaners. Acid base cleaning products are formulated to remove stains that are soluble in an acidic solution such as efflorescence that can leach from concrete, i.e. calcium and lime scale, and mineral deposits from hard water.
Sulfamic Acid is also somewhat effective for etching concrete. It is typically sold in a powder or crystalline form which can be dissolved in hot water. Once it is added to water, it is very similar to Sulfuric Acid. Sulfamic Acid is not as strong or corrisive as Muriatic Acid. It may be a better choice than Muriatic Acid for anyone not experienced working with acids. After using an acid base cleaner on concrete, it does need to be properly neutralized.