I have my quarter pannels sanded to bare metal treated with metal conditoner and primed with DP90LF How far do I need to sand back to bare metal when I am welding in the patch pannels and filling the vinal top mounting holes?ie.. how far from the weld bead will the DP be affected? I will not be welding more than a 1/2 inch at a time and will be hitting it with a air gun to cool it. Will it be verry obvios how much the DP is ruined and needs to be sanded back to bare metal and reprimmed? Thanks sorry this is so long. Zach

Let's put it this way, if you were to strip the primer off MANY inches from where you are welding, say six inches, what difference would it make? I mean, if you went two inches, or six, it really isn't that big of a difference.

Let me also say that you WILL be doing some plastic filler work over those seams. You don't want to try to keep the filler work small because there happens to be some good primer nearby. You WILL be applying plastic filler well past where any burnt primer will be, so don't worry about it.

By the way, WATCH the welding and cooling bit. I don't do that hardly at all, VERY, VERY selectivly. You are after all SHRINKING the metal when you cool the hot weld. It is hardly ever needed, taking your time between welds is MUCH better. Let the short weld cool naturally for a LONG time, ten or fifteen minutes even between welds will be much safer than cooling.

Zach Id remove that primer at least 2in from the weld zone. That DPLF is not something you want in your weld pool.

When I did my floor and braces I sprayed them first with epoxy. well on a spot or two I forgot to remove that epoxy good enough when I went to weld. Had all sorts of problems trying to weld.

Also PLEASE dont hit the welded metal with air or water. Doing so just makes MORE damage and work then you are trying to avoid. You are just stocking that metal into staying in that form(shrunken), if you allow it to cool naturally a good percentage of it will return to its prior state.

Its no different then using a torch to shrink metal, YOU AE DOING THE SAME THING

Makes sense will do. I know when welding thick stuff you are never suposed to cool it with water or air but I have talk to many guys that used air on body metal. Are 1/2 in beads about right on 18 gauge body sheet metal or can I weld farther when putting the patches in?

I would stick to welds shorter than the 1/2" with that being your MAX. The real trick is to spread it around. Weld one, let it cool a little then weld another as far as you can get from the first. Then let them both cool ten or fifteen minutes.
Come on now, I KNOW there are other things you can do on the car while it is cooling. smile.gif

Then go back and weld a few more the same way, over and over until it is done.

You need to re-align sometimes along the way, re-position clamps along the way, tap here and there along the way. Just take your time.