Go to Ace Hardware and get "Ospho". It's green liquid in a semi-clear bottle in the paint section. Also, get a trigger spray bottle to put it on with. It turns the iron oxide into iron phoshate (I think that's right...I didn't take chemistry) and you can paint over it the next day...or when it's dry. Be careful, the stuff's rough on the eyes and nose so use goggles and mask...and spray downwind. It will also turn your driveway white so be careful where you use it. Used properly it's great stuff and we use it a lot here on the coast.