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Finally gave in and tried a weld-through primer on a uniside job, wish I had done it years ago
Been doing this for about 8 years now and always just used regular primer and prayed the welds wouldnt burn it all off. Had a 2018 F150 come in last week with some rust on the rear uniside rail, and the shop foreman Tim handed me a can of 3M weld-thru. Figured id try it just to shut him up. Man the difference is night and day. No bubbling around the welds, no fighting to get the panel to sit flat. Saved me like an hour of grinding and re-priming that one spot. Has anyone else had a specific product change how they do a common repair?
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elliot543mo ago
Yeah @emmam32 nailed it with the light misting thing. I made the mistake of hitting it heavy my first time and the weld just kind of sputtered and wouldn't bite right. Learned quick that you're better off going light and letting it flash off before welding. The SEM stuff is thinner for sure but I still stick with 3M because that's what my supplier carries and I hate ordering stuff online. Either way it beats scrubbing off burnt primer with a wire wheel for 20 minutes after every repair.
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emmam323mo ago
3M weld thru is good but you gotta be careful with the zinc content on certain steels. I used it on a uniside once and had trouble getting the weld to penetrate right because I laid it on too thick. A buddy of mine swears by the SEM brand stuff, says it leaves a thinner coat that burns in cleaner. The 3M stuff definitely beats using nothing but dont just spray it on heavy and expect magic. A light misting is all you need, two thin coats if you really wanna be safe.
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