I live in a 2nd floor apartment and I let my cat lounge on the balcony. I have had an insect infestation on the balcony that I treated with a permethrin spray.
It's been 8 hrs since I sprayed the balcony and now I'm concerned whether to let my cat out. Is it safe, or if not, how can I clean my balcony so it is safe for the cat and so that washing it does not endanger other animals.
See International Cat Care. I agree with Separatrix that the balcony probably needs to be scrbbed down before you let your cat on it. If it were my cat, I'd consult my vet, bringing the bottle with me, and describing how much I used.
I doubt that rain will do a good enough job. Permethrin is oil based, and according to this reference can persist outdoors for days.
The National Pesticide Information Center discusses how to clean a permethrin sprayed surface, but you need to call their number (given at the bottom of the article) or visit your vet.
Permethrin in high concentrations is harmful to cats. In low concentrations it's used as a flea treatment, including for cats.
What you've used was probably a relatively high concentration since it wasn't used for flea treatment on an animal. You might want to wash the balcony down or wait until it's rained before letting the cat out. It's reasonable to be concerned.
