Worse than the inadequacies of the acid wash process are the dangers of it. Over time, it can destroy concrete as the acid weakens its structure.
Acid stains penetrate the porous concrete through a chemical reaction. The acid in the stain reacts with the concrete lime and inorganic metal salts. This chemical reaction creates a permanent color change.
Many contractors and homeowners use acid cleaners to wash their concrete flooring and exterior concrete surfaces. It's an effective way to remove rust, oxidation, water and lime deposits, and other contaminants that won't wash away with soap and water.
The most common acids used to clean concrete and bricks are hydrochloric acid (muriatic) or phosphoric acid. For many years it has been the standard cleaning method to prepare concrete for coatings installations, to remove stains of any type from concrete and to remove concrete slurry or efflorescence from bricks.
Acid-stained concrete is easy to maintain and will last indefinitely. You just need to follow several basic principles: Dust mop or broom sweep weekly to prevent dirt accumulation. Damp mop monthly to remove smudging, scuffs and water marks, and to restore gloss.
Alkaline cleaners are great for lifting oil stains, grease stains, and other petroleum-based stains from concrete. It's an added benefit that you can use it with a pressure washer, making the job that much easier. For an eco-friendly cleaner, we recommend Oil Eater cleaner degreaser (US$15.74, Amazon).
This will help the sealer to penetrate and result in a superior bond between the sealer and the surface. Sealing after acid washing provides long lasting durability and enhances or deepens the colour of your blocks, it is important to seal the acid washed area as it offers excellent protection against staining.
High concentrations of muriatic acid can etch concrete, glass, remove paint, dull chrome, and cause other issues.
Decorative concrete expert Jason Geiser, of Deco-Crete Supply, acid washes an area of concrete to lighten the color of stain. Acid washing is the process of removing the top layer off a concrete surface to open its pores and provide a clean slate for a coating.
Acid stains are a reactive coloring process that penetrates into the porous concrete surface. This is probably the most permanent of all coloring options but is usually limited to eight colors.
White vinegar will not damage your concrete. However, leaving this solution for an extended period will damage the cement that binds the concrete together. Hence, you should be careful when using vinegar on your concrete, especially if you will use this solution on polished concrete.
Stains are effective in restoring glaze to dull, shabby concrete surfaces. Slabs with none to minimal cracks, blemishes, and other flaws are ideal for staining. Stains enhance the appearance of the surface; they don't conceal defects.
The cost to install acid stains is around $2 to $6 per square foot for basic designs or $12 to $25 per square foot for complex colors and patterns. Acid stains, also called reactive stains, contain hydrochloric acid and metallic salts that chemically react with concrete to produce earthy colors.
The problems that are most commonly noted with acid staining are related to application. If too much or not enough stain is applied, the results can be unattractive. This can be corrected by using the correct amount of stain. Using heavy coats of stain does not always help color develop better.
Scrub the acid solution: Once the solution is applied, lightly scrub it into the concrete with a push broom or long handled scrub brush. This helps to create a uniform etch of the concrete. Let the solution sit from 2 – 15 minutes while it continues to fizz and bubble.
Muriatic acid is strong enough to etch concrete, but it can also cause severe injury and/or damage property when used improperly. Always wear protective clothing, rubber gloves, boots and goggles or a face shield when handling acid. Avoid breathing acid vapors.
Concrete Cleaning and Sealing: DIY vs.
DIY is certainly the cheaper option; homeowners will typically spend between $0.20 and $0.75 per square foot when cleaning and sealing concrete themselves, whereas that cost increases to between $1.20 and $1.75 per square foot when left to a professional.
Allow acid stain to react with the concrete floor for at least 6 hours. Clean residue and pour water on the floor to approximate the final color. If darker color is desired, apply a second coat. Clean residue from floor with degreaser and neutralizer solution using an acid brush.
The reason for washing the residue is to neutralize the acid. So long as you properly neutralize and rinse the concrete well a couple of times, it should be fine. Note: If you do not properly neutralize the stain, then the sealer will lose it's bond, which will then have to be stripped and re-applied.
Safer Alternatives to Acid Etching Concrete
The best alternative to prepping a concrete slab for an epoxy coating application is called mechanical grinding. Concrete grinding is when you utilize concrete equipment that is equipped with grinding tools (or discs) to remove the smooth top layer of a concrete slab.
In fact, vinegar removes mold from concrete better than bleach. Bleach will only remove the top layer of mold, causing the mold to return.