How do I remove old and set in cat urine smell and stains from concrete?

If it's pourous concrete (not smooth) then I'm not sure if my solution will work for you, but here are a couple of suggestions.

Remember: Always use proper ventilation and recommended safety equipment when using any chemicals!!!

Mop it with a bucket of HOT water and strong bleach solution (1 cup bleach to 1 gallon of water) Repeat one or two more times after floor has completely dried.

Gets some amonia and put it in a spray bottle and spray the entire area.

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White vinegar! I used this and it was a miracle.