davidr,

You are correct that bleach and cat urine do not mix well. Try Krud Kutter Mold and Mildew Stain Remover. It doesn't contain bleach and can be used for interior and exterior projects. I purchased mine at Wally World.
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I failed to mention you will find Krud Kutter in paint department.

Arjay, thanks for the tip. I'll try that next time.

After a lot of poking around the net, I found several suggestions calling for various amounts of TSP and borax. (Did you know you can make your own version of that popular $9 per quart mold control spray by mixing a gallon of water, 2 tbsp of borax, 2 tbsp of baking soda, and 1 tbsp of TSP?)

I ended up mixing about a half-cup each of Savogran TSP and Twenty Mule Team borax in 2 gallons of hot water, and scrubbing down the walls with it using a long-handled stiff brush (that stuff is downright vorpal if you get it on your skin). That and the power washer got almost all the nasty stuff off the walls.

The smelly floor is another matter. Phew! Nice kitties. (Not.) Anybody have a homebrew recipe for an equivalent of those expensive "enzyme" pet odor removers, such as Nature's Miracle?

Good information here, thanks for sharing.

A carpet installer some years ago recommened Oil of Wintergreen from the pharmacy counter. Diluted and put in a pump sprayer then saturate the concrete floor. Let sit and evaporate on its own. It worked quite nicely on dog urine stain/smell in a former home. Worth a try as the small bottle wasn't that much if memory serves.

And though not homemade but have had good luck with Odoban from Sam's/Costco. Comes in a gallon jug and you dilute as needed. I would use it full strength on the cat urine affected floor. Spray on generously and let air dry. It might be $20 or so but it makes a ton.