When to use them: These types of cleaners are primarily designed to remove stains, dirt, and contamination that are soluble in an acidic solution. They are especially effective for removing efflorescence on concrete, an insoluble metallic salt that appears as a white powder or crystalline residue on the concrete surface and will not wash away in plain water. Exposure to hard water, a high salt content in the concrete, and high soil alkalinity are common causes of these types of stains.
How they work: As you might expect, acidic cleaners contain acid as the active ingredient. They come in both concentrated and ready-to-use formulations and are applied directly to the contaminated area. Sometimes scrubbing or agitation is needed, and stubborn stains may need additional applications. It is critical to neutralize the concrete after cleaning with an acid-based cleaner, followed by a clean-water rinse. Consider using a sealer to protect the area from future alkaline or salt contamination.
Where to get them: Acid based concrete cleaners are available at most specialty concrete distribution outlets. Diluting standard muriatic acid is a widely used and accepted type of acidic cleaner. It is important to note that over-the-counter cleaners like Lime Away and soap-scum removers are designed to clean similar types of contamination in a bathroom environment, but do not contain acid, so they may not be as effective on concrete.
When to use them: Also known as “concrete degreasers,” alkaline cleaners are most often used to eradicate oil, grease, or other hydrocarbon-based stains in concrete. The high alkalinity of these cleaners emulsifies, or breaks down, the oily contamination. The other application for alkaline cleaners is to neutralize concrete surfaces after acid staining or acid cleaning. Alkaline cleaners are the best way to bring the pH of concrete from acidic to alkaline, which is concrete’s natural state. Modern alkaline soaps and cleaners far exceed the neutralizing ability of the old-school method of baking soda and water. They are economical too, since 1 gallon of cleaner fully diluted will treat approximately 4,000 square feet of concrete.
How they work: Alkaline cleaners typically come as concentrates and are diluted with water, depending on how aggressive the stain is. Apply the cleaner full strength for deep or older stains, and dilute it for newer stains that haven’t penetrated far. Agitation or scrubbing to work the cleaner into the oil stain is critical for good results. A common mistake when using alkaline cleaners is to not allow enough time for the cleaner to work. Depending on the type and depth of the oil stain, multiple applications may be necessary, with each being allowed to work for a few hours to get acceptable results. Another important step when using alkaline cleaners is to “lift” the oil stain out of the concrete once the stain has been emulsified. You can use an industrial wet vac, poultice, or rags. Remove the residue with clean water, and reapply more cleaner if needed until the stain is gone.