Things You'll Need
Stiff-bristle synthetic brush
Acid-resistant rubber gloves
Plastic drop cloths
3 tbsp. muriatic acid
Paint stir stick
Inexpensive garden sprayer
Concrete is a prominent masonry material due to its versatility, design flexibility and long-lasting sturdiness. Inconsistencies in moisture content, ingredients and ingredient proportions during the cement mixing process can cause discoloration in cured concrete. For instance, dark patches of discoloration on concrete are sometimes caused by the inadequate combining of calcium chlorine with cement. Although discoloration is not structurally damaging to concrete, blotchy coloring can detract from the smooth appearance of concrete sidewalks, porches, patios, walls and other concrete surfaces. Fortunately, there are remedies for discolored concrete.
Pour hot water liberally over the discolored concrete. Be careful not to splash the water onto your skin.
Scrub the wet concrete with a stiff-bristle synthetic brush to remove the dark blotches. Remove as much discoloration as possible from the concrete.
Examine the concrete for remaining discoloration. If darkened areas remain, gear up in long clothing, acid-resistant rubber gloves and safety glasses to prepare for use of muriatic acid.
Saturate the surrounding vegetation with cool water for protection against acid runoff. Cover any nearby objects with plastic drop cloths.
Fill a plastic bucket with 6¼ cups of cool water. Carefully pour 3 tbsp. of muriatic acid into the water to create a very mild acid solution. Using a paint stir stick, thoroughly mix the acid and water.
Flush the discolored portion of concrete with cool water to prevent the acid solution from permeating the concrete too quickly. Let the concrete dry for five minutes.
Pour the muriatic acid solution into an inexpensive garden sprayer. Spray the acid solution directly onto the discolored concrete. Let the acid solution permeate the concrete for 15 minutes.
Rinse the concrete with cool water to wash away the acid solution. Flush the concrete completely. Using paper towels, blot up the acid runoff to further protect nearby vegetation.
Dispose of the garden sprayer, paper towels and any remaining acid solution according to your local hazardous waste department's instructions. Do not flush the acid solution down any drain.
Muriatic acid is extremely corrosive and toxic.
Do not use muriatic acid indoors; the fumes can permanently damage metals and other household materials.
Pouring water into muriatic acid causes a chemical reaction that emits heat.