I just went through this on my rear fender project (still underway). I used
a good scraper knife with straight razor blades. I bought a pack of 100
razor blades for about $5 at harbor freight and went to town. Sometimes I
used a heat gun to soften things up a bit though only when necessary, as
scraping it off cold doesn't leave a residue, using a heat gun tends to. I
didn't have too much undercoating; and probably broke 10-15 razor blades in
the process.
Next I scrubbed the whole thing out with a stiff wire brush and a hose-
getting everything as clean as possible. Next step is to Por-15 the
underside of everything. Which actually brings me to a question: I cover
the back-side of all my welded areas with fiber-glass re-enforced bondo. I
use a disk sander to rough it out, but go ahead and leave it built up just a
little to help strengthen the area. The area around the weld is typically
surface rusted a bit; which the POR15 really likes to stick to. The POR15
also seems to stick really well to the bondo. But, I'm a bit perplexed
about what to do in the area right around the weld:
1) Bondo over surface rust, POR15 over bondo... will the bondo stick to the
slightly rusted surface OK? Will it continue to rust with a layer of bondo
between the POR15 and the metal?
2) Sandblast area, bondo and then POR15. Seems this might hurt the adhesion
of the POR15 to the metal in the area surrounding the bondo patch. And, I
hate to sandblast of a layer of metal in an already weakened (welded,
ground-down) area.
3) POR15 and then bondo (then maybe POR15 again). Will bondo stick to
POR15 OK? Will the POR15 stick well to freshly welded and ground metal (and
in many cases brand new metal patch panels). My experience has been that
POR15 really doesn't like to stick to new metal very well.
Up until now, I've been going with #1...
Ryan.
oletrucks is devoted to Chevy and GM trucks built between 1941 and 1959
|