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Discussion Starter #1
Should I put seam sealant in between lower cowl to firewall and upper cowl to lower cowl before plug welding? The assembly manual calls for something, I’m just not sure what. I found a video of some 3M urethane sealer used for spot welding. Is that ok, just clean around the plug welds?


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Seam sealer is applied after welding (and epoxy priming). Don't apply seam sealer to bare metal. I use Eastwood's... nice stuff but you'll need some Toluene to clean up.
 

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Discussion Starter #3
So, it’s good enough to seal afterwards? What did Ford use?




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Ford used a seam sealer that was as good as the alkyd enamel paints of the day.... it dried out, shrank and moisture got between it and the seam and "poof"..... rust. Much better seam sealers (and paints) out there today.
 

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Discussion Starter #5
I’m not quite to that point yet, I still need to get my frame rail/apron assemblies welded in, I’m just trying to make sure I have anything I need on hand before I get there.


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Ford used a seam sealer that was as good as the alkyd enamel paints of the day.... it dried out, shrank and moisture got between it and the seam and "poof"..... rust. Much better seam sealers (and paints) out there today.
Yeah, I didn’t see much effectiveness of whatever was there.




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Seam sealer is applied after welding ....
Not necessarily, weld through sean sealer are available and is used by the factorys and real body shops in connection with a spot welder. My cowl was assemblied with weld through sealer (using a spot welder) when the car was restored, The parts was epoxy primed and painted in the inside first, with only weld through primer were the welds should be.
 

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Discussion Starter #8
I found this, which is what made me wonder. Should I do something similar and clean the seam sealer off around my plug welds?
 

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I found this, which is what made me wonder. Should I do something similar and clean the seam sealer off around my plug welds?
Just remember that "plug" welding and spot welding are completely different. "Plug" welding is simply MIG or TIG welding two pieces together, through traditional welding, using the edge of a drilled hole as the point of contact. Spot welding passes an arc of electricity between 2 contacts, one placed on either side of the two pieces to be bonded. The amount of heat used is far less when spot welding.

While "weld through" products may be popular with production shops so they can make money when accepting insurance company labor rates, I'm not convinced they are the "right" way to do things. FWIW, unless someone has come up with some "miracle product", "weld thru primer" is generally speaking, just a simple primer with a high concentration of zinc. It's not a substitute for proper metal protection and, when subjected to heat, the zinc stays but the "paint" portion burns away.
 

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Weld though seam sealer is only for spot welding. Some may say they are compatible with MIG (wire feed) but if you read the manufacturer's instructions, you'll find they usually say MIG must be kept 2" away from the sealer. What that means on something like the cowl that has welds every inch or less, is that you can't plug weld with the stuff. A professional spot welder is just about all you can use with the stuff.

Another thing you could try is just using crash durable structural adhesive and not even weld. It doubles as a seam sealer. Ideally, it's used with spot welding or rivets.

I have a tube of this I was going to use Fusor® 2098 Crash Durable Structural Adhesive (Slow)
My plan was to weld the lower cowl on with plug weld then use this stuff from the upper cowl to lower cowl in conjunction with my HF spot welder but it just broke and it didn't work like professional spot welder and would require putting a lot of heat into the metal for more than 5 seconds each weld whereas the professional ones are probably on for less than 1/2 second and have timers. Regardless, I might just use the adhesive by itself with exception of a few quick stitch welds at the corners. I'll still fully weld down the lower cowl with weld through primer at the joints down below. Those aren't as critical for seam sealing since you can get to both sides of the seam. The upper cowl is different since you can't get to the inside seam after welding, hence why the structural adhesive might be the best bet there.

If going that route, make sure it's "crash durable" structural adhesive as it's much tougher than regular structural adhesive.
 

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Discussion Starter #12
So, the consensus is to plug weld and seam seal afterwards? Thanks for the input!


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Since my cowl was welded without any sealer when Dynacorn produced the body, I used some Eastwood chassis paint made for protecting the inside of the chassis. The paint can comes with a long tube that is inserted through holes, and the tube has a brass tip that sprays the paint. I used two cans on just the cowl, so hopefully that sealed it up.
 
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