2011 F350 rear fender rust spot and bubbles, does WoolWax help before installing fender flares?

[J Ryan]

Hi All,
I'm looking for some advice please. I know that Ford fenders tend to rust due to the foam insert holding moisture. My truck fenders started to bubble under the paint a few years ago and one just recently broke open exposing the rust. There are 2 bubbles about 3 inches big and the rust spot bubble that broke open is about 4 inches. I plan on going the fender flare route but conflicted on what to do so that it at least minimizes the rust spread. One body shop said they could grind down and prime but it will come back. I don't really care what it looks like since it will be well hidden under the fender flare, that is until it spreads. Another truck shop said that there is really nothing you can do and it will come back unless you replace the fender, not an option. They also said the best remedy would be to coat it with WoolWax like it is now which will seep into the rust and slow it down a lot. Then put fender flares over. The WoolWax seems like a good idea and simple too. Does anyone have any experience with this? Or any other options?

If this is an option I would guess I would have to break open the other two small rust bubbles to get some WoolWax in there too? Maybe get some of the loose rust flakes out.

I just did a full paint correction on this and it looks really good except the damn rust spot.

Thanks

[Bobby B.]

Once it starts rusting it just keeps spreading. I would think an underbody coating or a LineX coating would help slow down the rust from spreading quickly.

[Rsurfer]

I would think if you can stop the source of the moisture and then grind and primer the area it should last awhile.

[opie]

Once it starts theres no stopping it. Only slowing to prolong the inevitable. Wool wax or similar. I personally use fluid film. As long as it contains lanolin oil since it never actually dries. Best of luck

[DUBL0WS6]

On the outside I'd use a rust convertor and then cover with fender flares. On the underside, Woolwax would help seal out the water and air.

[J Ryan]

Update on this, and thanks for all the direction, greatly appreciated. I ended up grinding and sanding all of the bubbles to get the rust out which lead to a one inch hole that was eaten through from the rust. Then applying self etching primer on the outside and a couple spots on the inside. The I sprayed Fluid Film in the hole whatever I could reach side to side and on the inside of the fender. Put some Griots 3 and 1 Ceramic under where the fender flares would go, then installed the flares.

Boy, and uneasy feeling grinding away at my truck but I think the results are great now. I plan on taking the flares off in a year to see what it looks like and apply more Fluid Film and paint protection.