how to paint sheet metal that over Laps

mc1984ss

Frequent Racer
Apr 19, 2004
536
0
16
Wisconsin
I am repairing some rust on my core support. The patch piece will overlap another piece just like it did from the factory. I am wondering what is the best method to prevent this from rusting? Should I paint it with that through primer then weld the patch in? Or my second option was to paint it with do primer then grind away the paint to bare metal where so I can plug weld it? My guess is that even though some of the primer would burn away I think it would protect better than the weld thru primer but that's just my theory. What are your thoughts? Thanks in advance!
 

melloelky

Top Fueler
Jul 1, 2009
3,654
31
48
mass
your rite some of the weld through primer will burn away.what i do @work is prime the parts with the weld through,and when i 'm all done painting,i spray the seams/insides with an internal panel coating like 3m's rust fighter or transtars amber rust proofing.it runs into the blind areas that can't be primed after the repair.it runs into the crevice and coagulates and stays there.it offers some protection.it has a little red hose like the wd-40 cans so you can get into the hidden area.
 

Ribbedroof

Top Fueler
Sep 14, 2004
2,893
0
36
Rural Oklahoma
Just my opinion, paint the areas that will be covered with epoxy, then clean out the plug weld holes before welding. An old spotweld cutter can easily be modified to clean out the holes just where the weld will be.

Some automakers now specify that weld-through is NOT to be used (Chrysler, Toyota). I have read that there is some concern that using weld-through is actually making corrosion problemas more common. Do not know if it's the use of it, or the misuse of it that's the problem, I would suspect that it's the latter. I see many techs use it where a 2K primer should be used (inside open unibody rails, etc). It is not designed to be a long-term primer, but rather to be a sacrificial coating in inaccessable areas like pinchwelds.

Cavity wax is a great idea any time you have an enclosed area, use it all the time at work.
 

melloelky

Top Fueler
Jul 1, 2009
3,654
31
48
mass
Ribbedroof said:
Some automakers now specify that weld-through is NOT to be used (Chrysler, Toyota). I have read that there is some concern that using weld-through is actually making corrosion problems more common. Do not know if it's the use of it, or the misuse of it that's the problem, I would suspect that it's the latter.
hmm I'd be interested to hear more about this if you come across a tsb or something
 

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