"Larry Jaques" wrote in message
...
On Wed, 30 Aug 2017 21:27:09 -0400, wrote:

On Wed, 30 Aug 2017 11:20:00 -0400, "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

If you don't get ALL of rhe rust out, it WILL come back - but a
Wax-Oil reatment will drive out moisture and seal moisture out -
doing
a pretty good job of reducing rust. Bedliner just locks in any
moisture amd lets it rot from behind leavinf you a plastic fender.

How well does phosphoric prep/etch/rust-converter work in this
application?


https://www.amazon.com/Permatex-8177.../dp/B000HBNX38
"Not recommended for automotive exterior sheet metal repairs."

When POR15 first came out I called their tech help number and asked
about it for exterior rust spots. The girl said it wasn't recommended
for that use, but didn't know why, nor have I seen a reason more
recently.

When there is access to both sides I weld in steel patches, otherwise
I sandblast all the rust off the exterior. In some cases my
sandblasted repairs have lasted a decade, possibly because the back of
the panel or bumper was still intact.

The problem here apears to be rust that broke through from the back,
because the fender lip joint wasn't sealed well enough. I can barely
see some of the damaged area from the inside, let alone sand it or
scrub off all the factory caulk. I don't want to apply something
flammable that I can't remove later to weld.

The dealer's body shop would replace the entire quarter panel, for
more than the value of the car.

-jsw