Jim Wilkins wrote:
I have a persistent rust problem on the lower edges of rear fenders
where the wheel well liner blocks access to the back side. The lower
edge seam wasn't watertight and rust has perforated the outer and
wheel well liner sheet metal below the factory sealer bead, which was
applied from inside after spot-welding and didn't reach down to the
joint. I dug out most of it so I could MIG weld patches without
igniting it.

Several local paint suppliers have suggested 3M 08852 Cavity Wax Plus
to coat the inside of my larger welded and smaller resin patches to
prevent or slow the so far yearly rust lines along their edges. LPS-3
wasn't up to the task, or I didn't coat the out-of-sight area well
enough with it. The Cavity Wax comes with long applicator tubes.

I'd like advice on if it really works, and how difficult it is to
remove if for some reason it doesn't and I need to weld in a larger
patch.

The clerk told me it's better than rubberized undercoating in the
wheel well. The suggested alternative there is spray can truck
bedliner, assuming it can be removed if necessary.
tia
-jsw



Cavity wax is good stuff. Waxoyl is another good option.
Both spray in as a thin liquid and the carrier evaporates leaving behind
a thicker coating about like a heavy grease. Both are somewhat self
healing as well.

Both can be removed by heating with a heat gun, wiping off the majority
and using wax & grease remover to get the film off.

Have shot a LOT of both over the years. They both slow the rust WAY down.

Stay away from the rubberized stuff if you really want to stop rust.
That stuff tends to trap moisture under it. Bedliner is good IF there is
NO rust at all and you don't want to remove it.

--
Steve W.