Could I use JB Weld to fill some small gaps after weldind in a patch. Will it cause a problem with the new paint?
Thanks
Jan

If fixing the weld is not possible, I would opt to use fiberglass instead of JB Weld. Im no pro but thats my opinion. Of course, the best thing is to fix the weld or have someone else do it. You can also flatten out some copper pipe to place behind the sheetmetal when welding to keep from blowing holes in your sheetmetal. The weld will not stick to the copper.

If there are gaps, the welding is not finished. Don't risk using a filler. If moisture finds it's way through or if you use something that reacts with the paint, the paint job will be ruined and you'll end up doing it all over again. Do it right now and it won't come back to haunt you later on.

Tom

aluminum also makes a good backer for welding. soaks up heat almost as good as copper.

What about something like 'allmetal' (http://www.eastwood.com/usc-all-metal-2-1-lb.html) filler? I don't know if it's a good idea or not, just asking

What about something like 'allmetal' (http://www.eastwood.com/usc-all-metal-2-1-lb.html) filler? I don't know if it's a good idea or not, just asking

Great marketing name. No substitute for properly repaired metal. Yea, it's got metal in it but big deal. It's not going to stop H2O permeation through a missed hole and cause problems down the road. Floor pans and such are a little less to worry about but should be repaired properly nonetheless. I wish I came up with that product's idea and put it on the shelf.

keep welding. it helps to use a piece of copper on the back of the weld if you can reach to hold it, if you are having trouble with burn through.

I don't understand the common aversion to getting something welded up. it's not magic, and it ain't expensive really. now going back and fixing bad weld work after it's all painted and done, then that is a little more work. but why fix it half way and just invite the rust you worked so hard to get rid of to come right back. no thanks. fix it right once instead of having to fix it right the second time.