Noob looking to repair rust in car

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New to the forum, couldn't tell if this belonged here or the Projects section. I'm new to real world welding, many years ago I took adult ed welding classes and learned the basics, but never put them to the test with dirtier, thinner materials in a car.  My 2002 Impreza has lots of rot on the rear strut towers, this area is hidden from view on the inside, covered with undercoating in the wheel well so it doesn't have to be pretty. I'd like to extend the life of the car another 2 or 3 years. The bad news is there are two layers of material here, a thicker (about 18 gauge) outer layer that survived better than the much thinner inner layer. Looks like water got in between the two via some of the many holes in the outer layer that presumably are there to aid in assembly. I'd like to cut a larger patch out of 16 gauge and lap weld it over the affected area from the inside, instead of trying to create accurate patches to butt weld in. Is this a bad idea? It means I can get to the stronger metal away from the compromised area and not have to carefully create patches. Any thoughts, guidance?Thanks!GearLincoln 3200HDLincoln L56 .025 wire75/25 argon gas Attached Images
Reply:If you can you should always lap weld thinner materials, if its out of sight than a patch larger than affected area with lap welds
Reply:Cut out the rotten metal, if it's outta sight then go bigger and heavier, start with tacks or small welds with mig and move around, letting it cool and don't get in a hurry, it will distort if you get too fast and too long welding in one spot. Use seam sealer also when compleated and you should be good to go. On outer panels same theory applies but more precise at the joints and just little welds at a time and smooth them out with grinder then use autobody filler and sand and primer, Lot more involved. Good luck with it.Quality work is never Cheap, and Cheap work is never Quality!!If it's broke, and you're not, we can fix it!!  Lincoln Idealarc sp200Century 230amp ac/dcSmith O/A TorchesHuth Hyd. Pipe Benderother misc "cool" tools
Reply:Thanks for the input. I've cut out the rotted stuff, there's a good deal of mostly solid metal with pitted rust, is there something I should apply to that before covering it up? Would I also want to use a zinc primer? I don't want to go through this work only to miss a step and rust running amock again.Thanks.
Reply:I would first spray it down with encapsulator, then after that sets, flap disc off the surface. Then spray with weld through primer. Then proceed to spot weld or stitch weld the patch in. After that I would seam seal it, or get bedliner/rubberized undercoating and spray it wherever you can. Be careful not to trap any rust under it, as it will only become cancerous once again. Since its out of sight Id do both sides for good measure. And if you dont coat it, at least paint it. Bare steel will rust, and coupled with potential humidity that gets trapped under the trim, and in the matting, will only expidite the rust returning.Good luck
Reply:Looking into products to deal with the minimal amount of rust I have left is making my head swim. My local shop has SEM Rust-Seal, which seems like a viable option? My thought process is:Apply Rust-Seal to the exposed metal except for the edges that are going to get welded.Zinc primer over everythingLap weld on sheetPrimer over weldsSeam sealer where neededUndercoat it allDoes that sound right? I know prep is key, I don't want to screw it up and need to start over.
Reply:This is what you want for a weld through primer http://www.amazon.com/WELD-THROUGH-C...s=u-pol+primer It is copper based and you don't get burnt near as bad as with zinc spray when welding. Follow directions closely. I like to apply two light spray coats before plug welding panels on.Last edited by Slob; 10-09-2014 at 04:00 PM.SlobPurveyor of intimate unparalleled knowledge of nothing about everything.Oh yeah, also an unabashed internet "Troll" too.....
Reply:Get some practice material.  Lap weld as suggested.  Post pics and let the members here critique your welds until you are doing welds that are good quality.  That weld actually a structural weld as that area supports the suspension.   Also practice welding vertical.   As that is the position you need to welds in.Tiger Sales:  AHP Distributor    www.tigersalesco.comAHP200x; AHP 160ST; MM350P,  Spoolmatic 30A; Everlast PowerTig 185; Thermal Dynamics 60i plasma.  For Sale:  Cobra Mig 250 w/ Push-pull gun.  Lincoln Wirematic 250
Reply:All good advice. There are some really good tutorials over at metal meet - http://www.metalmeet.com/forum/index.php    Some real talented guys over there..
Reply:Look into a product called Ospho.http://www.crankshaftcoalition.com/w...val_with_Ospho I've used it with great results. Its easy to use and I can get it at a local Ace hardware store.
Reply:Things went pretty wel with the welding, the patches are in. I made a few small holes on the bottom edge, seems the material in the car was thinner there. Can I hit these with some seam sealer or do I need to plug them?
Reply:Me, my car, I'd make it perfect. Remember all the stuff you pulled out of there to get there. All the steps to get where you are. Do you want to redo any of it or ever look at it and think you could have done it better? But in the end, it's your car, do what you want. Likely "small holes" are not going to make or break anything if the rest of it is solid. It's just if they are small holes then welding them up shouldn't be the end of the world....