treating pitted metal before welding it in

I've got a panel that needs to be welded in but it's pitted and I don't want the rust coming back. I bead blasted it but thought a chemical etch would be a good idea, especially for places that won't be accessible after the panel is installed. The product I have is Eastwood Fast Etch (yes I contacted them, no I didn't get a good answer other than to buy their weld thru primer). The propoganda for it says "Fast Etch effectively dissolves rust and leaves a protective zinc-phosphate coating...all in 1 time-saving step"

Has anyone welded on metal treated with something like that? I planned to apply it and clean with prepsol before welding. Would I need to grind the metal shiny where I will be welding? FWIW the parts lay flat together overlapping, and plug welds in place of the original spot welds hold them together.

Thanks,

 

You are dealing with phosphoric acid, probably a diluted version of the acid.

This thread should be able to answer a bunch of other questions you may have on the acid:

http://www.jalopyjournal.com/forum/showthread.php?t=263091&highlight=ospho+welding&showall=1



What I recommend is cleaning the area you will be welding, simply put "make the metal shiny", the weld area will be contaminated with the acid and will not weld properly. once welded and ground down you can soak the area again to cover it with acid for more protection.

Good luck.

 

I have used a product made by 3M called "weld thru coating" with good results resisting corrosion.

 

Pitted or not, I epoxy prime the inside of panels that cant be reached easily after ***embly. If plug welding an over lap, after overnight dry of epoxy, I remove it, to bare metal with a rice cake or rolok type disk back about 3/4" from the weld site. I spray the bare metal the areas at the weld site with weld thru primer. After ***embly, I treat the enclosed area with body cavity wax. If there is no access I make one during the repair. Sounds like a lot of work, but I hate rust.

 

Thanks all. The unreachable part isn't inside a panel, it's between them. Once it's welded in I'll bury it in seam sealer. Just wanted to see what I could do to protect the areas that are (factory) lapped before the welding.