[962porsche]

if you did not use a direct to metal primer ( DTM) then the products will delaminate .
even most DTM primer don't like to stick to any galvanized substraight .
for the most part you will find at 1st it will chip very ez then later on it will start to peal .
you should have used a E-type primer ( Etch or Epoxy ) and one that is chromated . the only time you don't want to use a E-primer is when your using a product like feather fill also known as polyester spray filler or like product . if you use a E-primer under spray fillers the solvents in the E-primer will delam the spray filler about 6 months to a year later .

it is totaly NOT true at all that E-primers of old are better than ones offered today . in fact it's just to opposite !
the products now are of much better grade . the main content of epoxy primer is methoxy and propanol they are far better than even the same of 10 years ago . many people think that because products have to now be VOC compliant that they are less of a product .

the answer to the trivia is only a chromated primer does that .
chromates etch the substraight and only chromates do the etching .
propanol , methoxy and butyl benzyl phthalate is what bites into metals making them adhere . you will find DTM primers along with E-primers have one to all three of them .
because talc is the main content of filler primers it does not hold out any moisture . it does just the oppasite talc soaks up moisture . also talc offers no adhesion at all that is why you need a product like a E-primer under it over bare metals .