I was at Home Depot this morning and asked if they had any self etching primer. They didn't but what they had was phosphoric acid which said it is used to etch the surface of alluminum for painting. Has anybody used this before and does it work well? Cost wise it is cheap, only 14 bucks for a gallon and that will go a very long way. Just brush on and let it sit for 15 minutes and hose off.