Re: Fj Cruiser under coating
Anything applied over dirty parts can be worse than nothing at all, because it will then crack and tend to collect/hold corrosive moisture in the narrow spaces between it and what it was meant to protect. PVC undercoating is better than asphalt for this reason (it stays more flexible).
There are several threads on rust protecting your FJ, do a search. Quick summary:
0.5) wire brush off any red rust, the more you can remove the better everything else will hold up. Convert what's left from iron oxide to iron phosphate with something like Ospho, available from your local Sherwin Williams paint store.
1) clean all surfaces very well, starting with pressure wash (use a wand so you can concentrate on every nook and cranny), use oven cleaner on oily gunk that won't come off otherwise, and ending with brake cleaner to make each surface paint ready. Take your time, this stage is the most important. See above warning about poor adhesion leading to future, worse trouble.
2) brush paint a good quality primer coat, like POR15, onto everything (mask off brakes and rubber parts like parking brake cable housing and flexible fuel and brake hoses), then once dry go over that with a good quality black top coat paint (primer sticks to surfaces, top coat protects that from the elements). The primer and the top coat rely on each other for maximum life.
Note that the parts which will rust first are the frame and control arms and rear axle and the brackets for the bumpers. All of the black parts. The bottom of the cab itself tends to hold out for a very long time, due to what its made of. You can decide if you want to also do the cab or not.
3) after the paint stage is completed, then start in with the undercoating. Some use bed liner spray, or use a dedicated undercoating spray from a quality paint supply shop, or someplace like Eastwood.
4) after all of those coatings, then go over them with body wax, like Amsoil's Metal Protectant, or Waxoyl (there are several brands available). It is like cosmoline, in that it drys without leaving a tacky surface to collect dirt, and smells like a new car because new cars come with body wax coating their undersides.
5) after all of that, a lighter coating can provide additional protection, like Fluid Film (very easy to apply, penetrates small spaces well, but does tend to wash off over time, so re-application annually would be ideal).
Each layer protects the one beneath it, and each one provides the ideal surface for the one above to bond to.
Last edited by norm356; 07-16-2019 at 05:21 AM.