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.
Acid washing, also known as acid etching, prepares a concrete surface to accept a sealer. You can also use acid in weaker concentrations to remove white mineral deposits (efflorescence) and heavy grime. Acid washing is dangerous for people, plants, and metal objects, especially indoors where fumes can concentrate.
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. This will cause scaling, pitting, peeling, and cracking.
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-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.
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.
A small amount of acid added to the water will pull the stain out of the concrete without etching the concrete surface. In essence, the acidic solution reverses the reaction, allowing you to pull the color back out of the concrete.
While it corrodes almost anything it touches, this is not true of concrete. The acid works well on concrete and on many masonry projects because it neutralizes alkalinity. The surface becomes “etched” and clean, which allows for the proper adhesion of a new coating.
Usually this white or off-white discoloration to concrete and masonry forms when soluble salts and other water dispersible materials come to the surface through capillary voids as a result of temperature changes, moist migration, condensation, rain, dew, and/or too much water in the mix.
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.
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.
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.
The instructions with most acid stains (as well as concrete sealers and coatings) say to wait at least 28 days after pouring a slab before finishing it, with some recommending as long as 60 days.
But that's not all; chlorine bleach can also be used for cleaning the concrete driveway. Of course, you should dilute it with equal parts of water or a 1:1 ratio. With the mixture ready, spray it on the driveway, allowing it to sit for 10 minutes. Then, use a stiff brush before rinsing with clean water.
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.
Any concrete that is not properly neutralized will begin decomposing immediately. It may take time for the damage to reach the surface where you can see it, but it is happening and is usually irrepairable.
Vinegar or baking soda: These natural cleaners work well to clean cement patios with stubborn charcoal or rust spots. Mix equal parts vinegar and water, scrub the patio with the mixture, then give it a good rinse. If stains don't dissolve, try undiluted vinegar.
For mild discoloration, flush the hardened surface with hot water and scrub with a stiff brush to even out some of the variability in the concrete's moisture and mineral build-up. It may be necessary to carry out this process until the discoloration disappears.
Restaining works best if you need to go darker or fill in light spots, but does not work very well when you're trying to lighten the overall color. If the desire is to lighten the color, the best results I have seen come from pulling some of the initial stain out of the concrete.
Though new concrete may not always require a second coat of acid stain, older concrete does require two coats of stain for complete coverage. For a more diffuse look, spray the stain onto the surface without brushing.
Allow the acid stain to penetrate the entire concrete surface and fully develop its color for from 5 to 24 hours (check manufacturer's instructions for exact timing). The longer you leave the acid stain on, the deeper the final hue will be.
Acid stains or Chemical stains react with the lime in concrete and color the concrete whereas concrete dyes offer transparent colors to the concrete surface.