If using POR 15 my understanding is that you have to use a brush. There's no big mystery to methodology, from what I have read it cannot be sprayed without fatal consequences.
Please correct me if someone else has better information.
I use a siphon system on the end of my compressed air blower nozzle for doing things like that.
This way I basically blow the POR in without actually atomizing it like paint spray.
I use the elevation of the POR container to regulate flow.
And you are correct about wire brushing first being recommended, but sometimes it's just not possible and we have to settle for the best we can do.
And then I just realized you probably meant brushing the POR on and not prepping by brush.:D
