"Storage Primer" ??

[johnm]

  I recently purchased two replacement quarter panel skins for my 280SL from K&K Manufacturing which, by the way, has provided some excellent parts and great service over the 5 years I have been restoring my car. The quarter panels came primed (dark brown). We sanded prepped and epoxy primed the quarter panels but admittedly not down to bare metal. I recently had to mask a part of one quarter panel and upon removal of the masking tape the tape removed the epoxy primer and the primer beneath right to the metal. I enquired to K&K and was told the quarter panels were shipped with a "Storage Primer" only and that it has to be removed to the bare metal. I find that a bit puzzling as there were not labels or notes indicating this. Now it appears I must remove all of the epoxy and brown primer and start over with bare metal. Can anyone relay a similar experience or help me understand what I've encountered and what "storage primer" is?  Thanks

[andyburns]

The advice you have been given is good.  Epoxy primer is designed to seal bare metal.  Often it is extremely heavy paint and has a very high zinc content.  If applied to bare metal this gives excellent rust protection which is the main advantage of an epoxy primer. 

If the factory has applied an inferior primer for the purpose of storage and you paint over top of it your overall protection has not been significantly increased.  Sure you have an additional barrier but if the base primer lets go or there is rust under it from being stored for long periods then your no better off.

Usually the factory primer almost falls off when you put paint stripper anywhere near it.  Quite telling if you have ever stripped any epoxy paint before which takes quite a bit of removing.  It would only take a few minutes to get a factory panel back to steel.

Whatever you do don't blast it as this takes off a layer of factory applied zinc.  The panels prior to paint would have been dipped.  Chemical paint removal on factory panels off the car is by far the easiest and cheapest way to go.

Quite a few of these OEM and reproduction panels have also been sitting around for years waiting for the new owner.  More than often they haven't been stored in optimum dry conditions and the inferior factory storage primer has let itself down and allowed rust below its surface.  I have stripped back W108 brand new panels and found quite a lot of spider rust beneath.  I wish I had taken photos to show you.

If you don't treat this stuff I can almost guarantee that in a very few years it would grow and you would end up stripping the whole thing back again (or the next owner).  So at this point it is just one extra easy step and you prevent this kind of outcome.

[johnm]

 Thank you. This advise was very helpful.

[garymand]

Andy, how about the Alu?  I had a new door installed.

And, my trunk was paineted a long time ago and I freaked out over the orange peel.  The guy got a little miffed at my pickiness, re sprayed it and gave it to me the next day.  It has spidered and cracked.  I guess he glazed over the fresh paint and re-sprayed.  I'm not a body guy but I want to try to do this myself, at least to strip down my trunk and get it ready to paint.  What do you recommend?

[andyburns]

Gary, orange peel is the least of your worries especially with solid paint.  Much of it can simply be cut out given your solid top coat is thick enough.  Preparation of Ali is a different matter altogether.  Its actually quite pleasant to work with if you know what your doing.  Same preparation as steel with the exception that its much softer and rusts/oxidizes much faster.  Probably contentious but my opinion is that your better off stripping all the paint by hand with chemicals.  Commercially you will be talked into using media blasting to do it but that's probably because there is more profit in doing it this way for the proprietor.  

I stripped my bonnet back to bare metal with about 20 dollars worth of chemical paint strippers and then finished off with 400 grit and then 800 grit sandpaper.  When your sanding ali its apparent how soft it is so you have to be very careful not to go too hard or you can easily gouge it.  Even 400 seemed to coarse.

Once you have sanded it back to clean even surface you have very little time to get the sealer on. From memory you only have an hour or two once you have sanded off the ali till you have to paint it.  Just like standard steel you can get corrosion that creeps under the paint.

The sealer selection is also critical.  Not every etch primer is suitable for ali.  Check the spec sheet.  Again I went for an epoxy primer.  Chemically hardened with good anti corrosive properties and suited to adhere well to filler on top of it if required.  Once that had cured I sanded and blew another coat of conventional 2k etch one top.  This intermediate layer is better suited to take the final top color coat and is less likely to cause any frying or reaction.  I have heard of people that spray top coats right over the epoxy but all the research I did suggested that the additional etch is the way to to go.

Just remember its irrelevant how good the top coat is if what it sits on is a pile of poop.  I don't think this advice is anything that any competent corner shop painter would not also be giving you.

I am no expert painter as well so please treat this advice for what it is... coming for a part time amateur car buff who has done tons of research on youtube and google.