Two years ago I painted my 86 pickup. Now the seam sealer at the seams of the box has cracked and moisture is getting inside and i can see rust forming.

Im planning on sandblasting the seams and welding them solid to match the doors etc...

any advise/recommendations?

you can see pictures of it two years ago in my build thread

 

pointless .. dont waist your coin .

if you look undernieth , there are 3 layers sometimes 4 if at a support location . you will not stop it .. it is only a matter of time !!


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Welding the seems will only make it worse. The only way to eliminate this is to go with a fiberglass box. If you weld it you will only heat it up allowing rust to set in quicker.

 

You could also solder or even braze the seams. Or...dare I say...fill them with bondo(bondo won't leak a drop of water if it's painted, nor will it tend to dry out, crack, and/or seperate from the body panels over time).

None of that makes a lick of sense.

 

I think what he is saying , is if you weld , it will "burn off' any protection that is still there . the box "skirts" (lower portions of the box) are spot welded to the upper portion . When Toyota or California built them , only protection there was the ecoat on the pieces and then seam seal and paint .. If you weld it , it will burn off the ecoat , if there is any left , and excellerate rust formation


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Exactly......... Once it's welded you are loosing all if any protection do to the extreme heat caused my the welding. I guess if you were to get all seams on inside and outside welded to were no moisture can enter then you may be alright that way. Just make sure that you use a really good sealer to seal the bare metal prior to painting

 

Welding will burn off the factory coating(I think this is what Toyota~boy was trying to say), note I mean the zinc chromate or whatever the factory used not the under body coat vinyl stuff.

You'll need to unmount the bed to apply a rust preventer, paint, and restore the undercoat if you want to weld the seams. If you're not using a TIG machine you'll also need to grind out any inclusions.

You need to strip the seam sealer, treat the rust, reprotect the sheet metal, paint and then re-apply the seam sealer and if you can't match the color then paint over the sealer.

If you media blast you will remove the factory protective coat (zinc chromate or such), which you need todo to weld anyway aswell as strip the undercoat. You would normally want to use paint stripper this will leave the coating intact, it's also why you don't sand down to bare metal unless you have to, incase no one ever told you.