Epoxy and plug welds

J

jtfx6552

Member
I'm painting some parts prior to installation. Should I prime the whole panel including the plug weld holes and the places the plug weld holes will line up with?

Or should I mask little spots to keep the epoxy out and spray weld through in that area?

I'm an OK welder at this point, but I don't need any extra problems from primer vaporizing out of the holes, etc. I guess I don't know how tough this epoxy will be and how hard it will be to scratch down to the metal in the plug weld holes and around the edge of the holes in the mating panel.

I certainly would like as much protection on the panel as possible.
 
I would just epoxy the whole thing...no need for weld-through. When the epoxy is fairly fresh (within a day or so), just take a small screw driver and scrape off the epoxy inside the hole where you are going to weld. Sometimes I don't even scrape it off. You can weld right through the epoxy. I just think my welds come out better without contamination from epoxy.
 
Maybe Bob will come on later, but he posted on this issue not that long ago. I think the problem with having paint in the seam when welding, is the burnt residue left after welding. On doors, fenders,and other removable panels he suggested leaving it bare metal, and tape the seams after welding then pour epoxy in. Sounds good to me.
 
chevman;13584 said:
Maybe Bob will come on later, but he posted on this issue not that long ago. I think the problem with having paint in the seam when welding, is the burnt residue left after welding. On doors, fenders,and other removable panels he suggested leaving it bare metal, and tape the seams after welding then pour epoxy in. Sounds good to me.
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So, I guess you would tape onto the seam partially so the tape funnels the epoxy into the gap? Sounds like a good idea!
 
Yes, get the panel welded on and tape the bottom of the seam so it holds the epoxy from running out then flood the seam and let it cure.
 
So, for vertical seams like a cab corner, A-pillar patch or quarter skin.......use an auto twirler? (grin)
 
I did as Bob says on a truck inner bedside-to-floor seam and it worked out great. It was nice to see a layer of epoxy between the seam when I untaped it. Thanks, Bob!
 
Do not try to weld thru the epoxy. The weld will be dirty and I would not trust them to hold. Put the epoxy on it after welding, like Bob says. That way everything is sealed.

Aaron
 
I like to epoxy before putting the two panels together, put the panels together and then take an end brush and clean each plug weld hole before welding.

end-brush-bridled.jpg
 
Cleaning the plug weld hole is a must and it will work but oftentimes if there's a few coats of epoxy the contamination will make for more chance of blow through or burn back. It's suggested to clean the holes when using weld through primer also. The fresher the epoxy in that weld area the more difficult the weld will be. A spot blaster also works really well. I like clean bare metal, weld, then coat... but some areas are more difficult than others. After doing some corrosion resistance testing on weld through primers years ago I came to the conclusion the protection they offer is very minimal and I wouldn't want it in there if I planned to flood the seam with epoxy and seal it.
 
C10chas;13604 said:
So, for vertical seams like a cab corner, A-pillar patch or quarter skin.......use an auto twirler? (grin)
Click to expand...

A rotissery helps position the seam for sure but that verticle cab corner seam-you could tape it completely shut except the top and fill it-takes awhile but if it'll run in it will fill up.
 
I have never used a spot blaster to clean the holes, but it sure would do the job. My little shop isn't the best place to be abrasive blasting or I would give it a go .
Maybe next spring I will get a concrete slab poured in front of my shop so I can roll a project outside and work on it.
Was going to pour the slab this summer but never got to it as life got in the way :(
 
Senile Old Fart;13625 said:
I like to epoxy before putting the two panels together, put the panels together and then take an end brush and clean each plug weld hole before welding.

end-brush-bridled.jpg
Click to expand...

I couldn't find any "end" brushes locally that looked like they'd work good. Smallest I found was 3/4" diameter, they are stiff enough that it reall couldn't get in and clean the edges of the base panel. After calling spiral brushes, who told me a few distributors to call, I did find some smaller diameter, (1/4" and 5/16") at McMaster Carr. They haven't arrived yet, but I think they'll be great to clean out the hole and the edges of the top panel.

http://www.mcmaster.com/#end-brushes/=elnixi
 
A larger one will end up about 1/4 to 1/2 inch after it's been well-used
 
For those who cannot or will not take the time to completely saturate seams with epoxy, or where the ability to do so is in question, weld-through primer remains a good choice that is still recommended by leading authorities on collision repair for panels that are not zinc coated from the factory, or where the factory zinc coating is not intact.
 
I've got a question pertaining to this old thread. On my new trunk pan, I removed the original vapor canister bracket from the old one. I have epoxied both pieces. The white bracket I have marked the holes with a sharpe and ground this area to bare metal with a cone carbide tool. I have also took an exacto knife and cleaned out the inside of the holes on the pan. Is this all I should do prior to welding? Thanks.




Off topic, for you guys that have used SPI's white and black epoxy, does the white seem to smell more than the black?
 
The primer shown was painted on the rear tailgate opening, and also on the underside of the tailpan. This provides rust protection where in many cases the factory process does not add any paint until after assembly. In cars like this 55, in many cases the inner voids such as in the rockers or floor cross-members never receive any paint finish inside, making them especially prone to moisture and rust issues. You will need to clean the paint off the adjacent panel within the drilled plug weld hole for a good weld.


Picture314.jpg



Which is what brought about the need for this tool, the same size drill bit I used for plug weld holes is flattened and backfaced to resemble an end mill cutter.


Picture315.jpg



Picture316.jpg



This shows how it works, cleans the paint from the metal surface, but having a flat face on the cutter, it doesn't remove the metal as a regular drill bit would. Notice most of the "chips" are paint....


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And welded......


Picture321.jpg



Some guys will use a weld through primer to accomplish this same process, I prefer the epoxy as I read an issue of Auto Restorer magazine quite a few years back that a study showed epoxy offered better long term protection from rust. No matter whether you choose weld through or epoxy, either will be better than nothing at all.


For normal application, I spray inside my paint booth. For a small application like you see here, I'll mix up some epoxy and brush it on. (note brush strokes in first pic above) Again, the application process won't matter much as any exposed epoxy will be sanded and re-applied later, but now that we have some epoxy between the two panels, there is better rust protection regardless of how it got there.
 
Thanks Robert. I need to make a drill bit like that one. I plan to scuff and re-shoot once everything is welded.
 
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