Consensus on Lap Joint Weld Prep? |
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Consensus on Lap Joint Weld Prep? |
bkrantz |
Dec 17 2019, 09:45 PM
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#1
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914 Guru Group: Members Posts: 8,066 Joined: 3-August 19 From: SW Colorado Member No.: 23,343 Region Association: Rocky Mountains |
So based on experience and expert knowledge, what's the best way to prep metal for lap joints, especially with plug welds? No paint or treatment? Ospho? Weld-through primer? And what about seam sealant after welding before paint?
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Literati914 |
Dec 17 2019, 11:42 PM
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#2
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Senior Member Group: Members Posts: 1,670 Joined: 16-November 06 From: Dallas, TX Member No.: 7,222 Region Association: Southwest Region |
Scuff to clean metal, then phosphoric acid, let dry...then clean w/ wax grease remover, then epoxy prime, let dry...plug weld, scuff away slag, grind if needed, then epoxy prime the exterior of the new seam, add seam sealer... then the top of the sealer will get epoxy primed again before paint, of course.
There's more than one way to skin a cat but I've read at least a couple of articles that compared weld thru primer with just using epoxy primer.. and the EP was the victor. So, anyway that's the technique I favor, one less item to buy, if nothing else (I've paid good money for Weld Thru primer that wouldn't spray too), YMMV. |
bbrock |
Dec 18 2019, 09:00 AM
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#3
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914 Guru Group: Members Posts: 5,269 Joined: 17-February 17 From: Montana Member No.: 20,845 Region Association: Rocky Mountains |
Scuff to clean metal, then phosphoric acid, let dry...then clean w/ wax grease remover, then epoxy prime, let dry...plug weld, scuff away slag, grind if needed, then epoxy prime the exterior of the new seam, add seam sealer... then the top of the sealer will get epoxy primed again before paint, of course. There's more than one way to skin a cat but I've read at least a couple of articles that compared weld thru primer with just using epoxy primer.. and the EP was the victor. So, anyway that's the technique I favor, one less item to buy, if nothing else (I've paid good money for Weld Thru primer that wouldn't spray too), YMMV. (IMG:style_emoticons/default/agree.gif) This was my process too. Only thing I'll add is that you need to scratch away the primer inside the plug holes with a scratch awl or screwdriver before welding. That's true even if you use weld-thru. I started my resto using Upol copper weld-thru which is really nice stuff, but I noticed it was burning back from the welds just as far as epoxy so I switched to just using epoxy to save money. More black soot with epoxy than Upol but otherwise seems to be a similar end result. I also followed the welding by brushing the edges of the seams with reduced epoxy to let it seep into the joint. |
FL000 |
Dec 18 2019, 01:43 PM
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#4
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Member Group: Members Posts: 422 Joined: 31-January 12 From: Lancaster, CA Member No.: 14,076 Region Association: Southern California |
This was my process too. Only thing I'll add is that you need to scratch away the primer inside the plug holes with a scratch awl or screwdriver before welding. That's true even if you use weld-thru. That's interesting. I am a novice welder, and I always had less than satisfying results with the myriad of weld-through primers I tried. I just assumed weld-through was meant literally! I'll keep this in mind for future projects. (IMG:style_emoticons/default/beerchug.gif) |
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