Because they aren’t especially porous, horizontal concrete surfaces don’t accept paint or epoxy coatings very well. Without treatment to promote adhesion, these finishes chip or peel over time, especially under heavy foot traffic. Acid washing solves that problem, but it’s the most hazardous DIY project most homeowners will ever attempt on concrete. We’ve worked on Denver slabs since 1988, and we’d rather you read the safety section twice than learn any of it the hard way. Here’s our step-by-step guide.
What Is It?
Also called acid etching, acid washing prepares a horizontal concrete surface to accept an epoxy coating, paint or a sealer. In weaker concentrations, acid can also strip heavy grime or white mineral deposits. Don’t confuse acid washing with acid staining, which is meant to add color to concrete. An acid wash isn’t needed before applying a concrete stain.
Safety Before Anything Else
Acid washing is dangerous for people, pets, plants and metallic objects, and doubly so indoors where fumes concentrate. Before you open a single container, gear up: rubber boots, acid-resistant gloves, vapor-proof goggles, and a respirator with a professional, acid-grade filter. Cover all exposed skin with clothing, and wear a face shield plus butyl or PVC coveralls or an apron.
Keep fresh water nearby to rinse spills from clothing or skin. Keep garden lime or baking soda on hand to neutralize any accidental acid spills on the ground. If any of this feels like more than you bargained for, that’s a legitimate reason to hire out the work or pick a gentler method.
Alternatives Worth Considering
Acid isn’t the only way to prep or clean a slab. If your goal is simply a clean surface, a pressure washer and a concrete degreaser handle most grime with far less risk. If you need etch-level roughness for a coating, mechanical grinding with a rented concrete grinder produces a similar profile with dust instead of fumes, and many coating manufacturers now sell milder etching products formulated to be safer for homeowners. Acid washing earns its keep on large areas where grinding is impractical, but weigh the alternatives honestly before committing.
Step 1: Clean the Surface
Thoroughly clean your concrete surface, removing all dirt and grease. Start by sweeping or vacuuming up dust. If there are oil stains, clean them with an alkali detergent or concrete degreaser, then rinse well with clean water.
If water beads up on the surface, the acid wash might not work correctly. Degrease the surface and test it with water again. Avoid trisodium phosphate (TSP) cleaners, which can leave a residue that reacts violently with acid and releases very dangerous gas.
Step 2: Select an Acid
Choose an acid that matches your experience level and the location of the project. Sulfamic acid is the safest to handle and the one we’d point do-it-yourselfers toward. Phosphoric acid gives off fewer fumes and suits areas containing acid-vulnerable materials, including stainless steel. Muriatic acid is very strong, produces intense fumes, and belongs in professional hands only.
Step 3: Prepare the Acid
Mix the acid and water in a plastic bucket. Never a metal one; only plastic resists acid concentrations. To prevent a violent reaction, add water to the bucket first, then slowly pour in the acid. Consult the manufacturer’s guidelines for the water-to-acid proportions.
Step 4: Prepare the Surface
Hose down the slab so the concrete is damp but not puddling. Wet surrounding objects such as bushes, trees, doors, door frames, walls, carpets and cabinetry. Shield drywall or asphalt with a plastic drop cloth. Keep the concrete wet the entire time you work, dividing large surfaces into smaller sections and re-wetting as needed.
Step 5: Apply the Acid
Gently sprinkle acid onto the surface using a plastic watering can, working in small sections and pouring low to the ground to avoid splashing. The watering can will likely corrode in under an hour, so have several replacements ready. Follow the manufacturer’s instructions on how much acid to apply.
Step 6: Brush the Acid
Immediately after applying the acid, distribute it evenly with a long masonry brush or push broom. Then wait 5 to 10 minutes while the acid etches the surface.
Step 7: Rinse and Neutralize
To avoid damaging the concrete, scrub off all remaining residue before the acid dries, using a long masonry brush and plenty of water. Next, mix a cup of household ammonia, garden lime or baking soda into a gallon of water. Scrub the mixture over the concrete and let it sit for about ten minutes. Properly etched concrete has a uniform texture close to medium-grit sandpaper.
Rinse the surface several more times and dispose of leftover acid according to the manufacturer’s instructions.
Colorado Notes: Dry Air, Fast Evaporation, Runoff
Denver’s low humidity and strong high-altitude sun evaporate water off a slab startlingly fast, and a surface that dries mid-etch can end up blotchy or damaged. Work in smaller sections than the product directions suggest, keep a charged hose within reach, and schedule the job for early morning or a cool, overcast day rather than a July afternoon. Skip windy days entirely; wind dries the slab and carries fumes where you don’t want them.
Think about where your rinse water goes, too. Acidic runoff shouldn’t reach lawns, garden beds, or the storm drain, which in most Colorado municipalities flows straight to a creek. Neutralize wash water before disposal and check your local rules on concrete rinse water. A little containment planning keeps a weekend project from becoming a neighborhood problem.
Things to Consider
Before you etch or refinish a slab, confirm it’s in good condition. If the surface is sagging or cracking, you can have it restored at an affordable price using mudjacking techniques, perfected by AAA Concrete Raising. Give us a call at (303) 526-2222 and we can level your concrete surface before you begin work.
AAA Concrete Raising has served Colorado homeowners and businesses since 1988. Our crews use modern equipment that skips the noisy, awkward machinery, delivering a speedy, neat job that won’t disrupt the neighborhood. Contact our team for all your concrete restoration needs.
