Although concrete is a very hard and durable material, it is porous and absorbs stains and holds odors. If your cat has urinated on your unsealed indoor or outdoor concrete, you need to use chemicals stronger than typical household cleaning products to remove the ammonia smell for good. It's also important to seal the concrete afterward to prevent pet urine and other substances from penetrating it again.
Wash the Stained Area
Before using stronger cleaners to remove all traces of the cat urine, wash the area with a mixture of warm water and a biodegradable detergent. You also can use a combination of 1 part distilled white vinegar to 2 parts warm water. Apply the solution to the urine-stained area using a bristled scrub brush, working it into the concrete. Allow the area to thoroughly air-dry before continuing.
Cat Litter and Bleach Approach
When the concrete is dry, sprinkle some clean clay cat litter onto the area and rub it into the flooring using a wood block. Work the litter into the concrete for about a minute to open up the porous material and prime it for the bleach solution. Next, fill a bucket with half water and half bleach, and slowly pour it over the stain, covering the entire area. Allow the cleaner to sit on the concrete overnight and clean the area with a soap and water mixture the next day. Open windows to provide adequate ventilation while using the bleach.
Trisodium Phosphate Crystal Approach
If you still smell cat urine after trying the bleach solution, fill a bucket with 1 gallon of hot water and pour in 2 pounds of trisodium phosphate crystals. In a shallow enamel pan, slowly add water into 12 ounces of chlorinated lime until it forms a paste. Combine the trisodium phosphate solution with the paste in a clean plastic container and add warm water to create 2 gallons of cleaning solution. Pour a 1/4-inch-thick layer of the solution directly onto the urine stain and sprinkle on enough powdered talc to create a thick paste. Allow the paste to thoroughly air-dry, and then scrape it off and dispose of it. Clean the area with a soap and water mixture. Make sure to ventilate the area and use gloves and safety glasses when handling the materials.
Seal the Concrete
After the cat-pee stain and smell are gone, seal the concrete to make sure the incident doesn't happen again. Apply concrete sealer to the flooring according to the manufacturer's directions. Not only does the sealant make the concrete moisture resistant, it gives it an attractive shine.