<< I recently dropped off my GMC cab at the acid dippers, when it is
finished, it will have a phosphate coating sprayed thru and thru. >>
There are two phosphate coatings. One is iron phosphate which would be on
the metal if dipper uses phosphoric acid as his main dip. After rinsing he
might use a CONVERSION COATING which changes the iron phosphate to zinc
phosphate. This is what the OEMs use--both steps. Ask dipper if this is the
case, and what he recommends for further coatings. If you don't trust his
advice, go with an etching primer such as PPG DX1791. One light coat is
enough, but you want to get it into all seams and to the backside of as many
panels as you can. After that go over all surfaces with epoxy primer. If
your truck was AD black is right, such as PPG DP90 or DP90LF, the new
formula. If you have welding to do one light coat in that area is enough, as
it will burn off in welding (Should be removed before welding, but may not be
practical in hidden backsides.). Use 3 coats where welding is not necessary.
You can do body filler on top of this in a day or two.
I covered metal prep and priming in detail in THIS OLD TRUCK magazine within
the past year. I was school trained by PPG and have 30 years of OJT in chevy
truck restoration.
You might also ask dipper for references from happy customers whose paint
jobs have had time to age. The big problems with dipping is acid left behind
in seams which leaches out and discolors paint topcoats or lifts it off, and
lack of protection on the backs of hidden surfaces.
Sanding should not be necessary and is not advised as the acid roughs up the
surface sufficiently.
If dipper uses HCl--muriatic acid--it will ruin subsequent paint work. Stay
clear of that.
Bob ADler
Adler's Antique Autos, Inc
oletrucks is devoted to Chevy and GM trucks built between 1941 and 1959
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