Cat urine contains both uric acid, pheromones and other waste products that give it a potent odour. Unless sealed, concrete is a very porous material that the urine saturates, leaving a stain and a lingering odour. Unlike other surfaces, you must take special steps to clean the urine from concrete since the urine becomes trapped within the porous material and will continue to emit the odour whenever it comes into contact with moisture.
Sold in pet stores, you can purchase enzymatic pet urine cleaners to treat any urine stains on concrete. These cleaners contain enzymes, which break down the urine, and harmless bacteria to digest the organic ingredients of the urine. Use enzymatic cleaners to treat the area of the stain before using any other cleaners, which can dilute the ability of the cleaning bacteria. Completely saturate the area and any area surrounding the stain to completely remove all of the urine. Since the concrete is so porous, you need to ensure the cleaner does not dry too quickly for the bacteria to work. Soak a towel in the enzymatic cleaner and cover the area of concrete with it. Place a plastic tarp over the towel and let the area dry for 24 to 48 hours.
Chlorine bleach can help eliminate old urine stains and odours. Mix up a solution of one part bleach and nine parts water. Pour the bleach solution over the stain, saturating the area, and allow it to dry overnight. Reapply the solution if necessary. Use a scrub brush on the bleach to clean away any stains on the surface. The bleach will disinfect the concrete, killing any odour-causing bacteria that has formed in the urine and fade the stains left by the cat urine. The bleach scent should dissipate within a few days.
Mix vinegar with two parts water to form a more environmentally friendly urine cleaner than chlorine bleach for the concrete. Spray or pour the vinegar solution on the urine stain. Sprinkle the surface with a paste made from baking soda and hydrogen peroxide to scrub away any stains on the surface of the concrete. Sweep away the baking soda when the solution dries. You can treat the area again with either the vinegar and water solution or pour hydrogen peroxide into the stain and allow it to dry. It will naturally bleach away any stains and kill any bacteria left in the concrete from the urine.
You can use vinegar, hydrogen peroxide, chlorine bleach or enzymatic cleaners to clean urine from concrete. These cleaners, especially the enzymatic ones, work best on fresh stains. For older stains, the odours may remain even after cleaning, especially in concrete subfloors. If, after cleaning multiple times, the stains and odours remain, you need to seal the concrete to keep them from seeping through. Purchase a special oil-based primer and sealant that you paint directly over the urine stains. Wait until the coat dries and continue to apply as many coats as necessary to keep the stains from seeping through the sealer. This will eliminate the stains and odours completely.