POR-15 is a rust encapsulator, meaning when dry it forms an impervious coat or cover over the rust so it cannot obtain oxygen and keep rusting. As long as you remove all the loose rusty material, dust, flakes, and larger chunks, it can be applied right to the otherwise existing surface. Application can be by brush, roller, or even by gun as there is a specific reducer for the stuff. Depending on what kind of finish you are seeking, gun might give the best results. Use a cheapy for your shot because by the time you finish the gun will be junk. Be very aware that if you get it on any surface including yourself, that you don't want it on, you need to remove it immediately. Once it sets or hardens, you'll need to use a mini-grinder, or lots of hand sanding, to get it off. That includes human skin as it cannot be removed from that either. Only thing that works is time. Hee, heee, heee.
