patch panels ???

Hello,

I'm getting ready to install some sheet metal patch panels to combat some rust in an old truck that I own. When spot welding the patch panel in place what is typically used on the bare metal surfaces (flanged sections that overlap and are spot welded) to combat rust? I know paint is not a good idea as it can contaminate the weld. I've heard of coating the welding surfaces with a Zinc weld through product but not sure if this is correct either. I don't want to leave the flanged edges bare as I'm sure that rust will form again between the pieces of metal.

Any help would be appreciated!

I'm not exactly sure of your question. I assume you are concerned with the back (non-appearance) side ?

What I've done is sand all metal clean, then wipe with a prep pre-paint wash (DuPont 'Quickprep' is one, I think). These are mild acid solutions to remove micro-corrosion.

Then I weld panel in place. When I can get at the back of the finished patch, I coat with roofing tar as an undercoating. The grind, prep, prime, paint appearance side.

Good luck !

Weld through primers are excellent, however, despite their fancy name they are no more than a Zinc rich primer available at any industrial paint vendor in brushable form or to thin for spraying.

Here in UK I recently paid the equivalent of 40 dollars for a gallon (that is a similar price for only 3 small so called weld though primer aerosols) The paint is so heavily loaded with Zinc that I could hardly lift it off the counter.

I coated both flanges and the complete inside of the sill (rocker), that I was about to spot weld, with a brushed coat of the primer and waited for it to dry. It worked a treat the zinc in suspension maintainted the electrical contact with no problems.

As a side issue it is also an amazing product when sprayed. I thinned 50/50 as I would ordinary primer and applied to bare metal, painted areas and bondo skimmed areas in my engine bay. When dry it appeared as primer would, a nice grey matt finish. The surprise came when I started to prepare for the next coat. When rubbed down it becomes a metallic finish with excellent pin hole filling properties. It took the next coat of primer no problem.

I highly recommend it's use and I hope that the paint's properties will keep rust at bay.

Adrian Dix-Dyer Repatriated Triumph TR4A under restoration.

Can you please share the brand name of the zinc base paint you used ?

As requested the name of the product is:

Firpavar 178 Zinc Rich Primer.

Manufactured by Firwood Paint and Varnish Company Bolton, Lancashire,