Welding - back side rust question

[Argeo]

Hi,

Just wondering what people do to prevent rust on the hidden side when a new piece of metal is welded into a spot that is not accessible after the piece is welded into place. I would think you could POR-15 the back but the seams would still be unprotected. Is there anything that should be done to protect the seams or is this just a problem with no solution?

Thanks,

David

[Tim K]

Prime what you can with a non-porous primer/paint and use weld through primer at the seams. I still drill through both panels when spot welding at a seam (outer 1/4" and inner 1/8") otherwise I have problems getting good penetration using only the weld-through stuff and a hole in one panel. I use an old copper tip from a MIG for a back-up (copper won't stick).There was a thread a little while ago about the weld through primers. If I remember correctly the Wurth product was getting the most positive response.

Tim K

[Argeo]

Thanks Tim.

What is weld through primer?

David

[Tim K]

It's just zinc rich paint in a rattle can. Easy to apply and dries fast.

http://www.wurth.com.au/a030311.asp

Tim

[Argeo]

Alright Tim, now I am confused. How is the back side weld seams protected if it is painted on? It can't be painted over the seams once the sheet metal is welded into place. Back side is not accessible. Am I missing something here?

Thanks,

David

[deoxford]

Argeo: I have been thinking about that also.. I welded some parts on the car and I painted and primed the outside but how do you get the back side painted is a good question. I was thinking of using some POR-15 in a spray bottle and catching the left overs a few time till al is coated.

[Argeo]

Last night I painted some sheet metal with POR 15 that I will use for some of those places I can't get at afterwards. Year, I am not sure about the actual weld though. Maybe I am being picky but if the area rusted out before, obviously it is an area that sees dampness from time to time. I guess I will just watch out for puddles.

David

[Zeke]

The heat from the weld will make the back side vulerable to rust. Sometimes you can turn a spray gun down to a stream, but you need a pressure pot to do so. Rattle cans can get into some places thru an opening nearby.

With the little straw attachment, you can use this. Get the spray cans. I've tested it for a year now and it works as it says, on a maintenance program. Not a one time deal. I'm testing a cosmoline based spray now and the rust hlod out looks good. I've eliminated a product, as well. It failed to do much.

I'll have more info soon.

[Argeo]

Thanks Milt.

David