Re: '84 5kS touch-up paint/galvanization question

["Fred Munro" <munrof@isys.ca>]

Benedikt;
    I have attached a list of rust repair tips I posted to the list some
time ago. I hope you find the info of some use.


   > I have developed a rust repair techique over the years which gives good
results.
    Sandblast the rusted area to bare metal and sandblast back to the
unrusted metal at the circumference of the spot. Feather-edge the paint
around the sandblasted area with 400 grit wet paper.
    Treat the bare metal with a phosphoric acid-based metal prep solution (I
use Dupont M3 Metalprep).
    Prime with an epoxy primer (I use Dupont Corlar)
    Prime again with a two part urethane filling primer ( I use Dupont
1044R).
    If you are using bodyfiller (heaven forbid!), apply it after the priming
is done. Bondo and it's ilk is not known for rust-resisting properties.
    Sand smooth with 400 grit wet paper (followed by 600 grit wet paper if
applying a clearcoat finish).
    Topcoat with matching colour. The new basecoat-clearcoat systems are
easy to use and to blend with the existing paint.
    I use wet-on-wet application techniques. You don't have to sand between
coats and you get a chemical bond (the paint systems have to be compatible).
    The success of the repair is in the primer system; the topcoat just
makes it look pretty.
    The galvanizing applied to this type of repair is a spray cold
galvanizing. It is basically a zinc-rich paint. It does not perform as well
as the hot galvanizing applied at the factory (a layer of molten zinc metal
applied to the surface of the steel). I personnaly do not use the zinc
spray, but it is recommended in the Audi procedure. IMHO it would only be
useful if the repair failed, and then you'd have to redo it anyway.
    Repairing the rust on the rear wheel wells takes special care. If it
shows up on the outside, it has usually progressed under the liner to the
bodymetal joint. If the rust gets a good footing in this joint, it is
extremely difficult to do a lasting repair. You have to remove the plastic
wheel well liner and sandblast the rusted area to bare metal. Prime as
described, and fill the joint with a sealing compound ( I use 3M Dripchek).
This type of rust failure is common to cars repaired in a bodyshop - if they
take the time to do it right, they won't make any money or would be deafened
by the screams of anguish when the customers saw the bill.

HTH

Fred Munro
'91 200q  261k km
-----Original Message-----
From: G. Benedikt Rochow <rochow@segosf.hlo.dec.com>
To: quattro@coimbra.ans.net <quattro@coimbra.ans.net>
Date: Tuesday, October 27, 1998 7:16 PM
Subject: '84 5kS touch-up paint/galvanization question


>
>
>This car has some large paint chips, and subsatntialy rust on some of them,
>on the hood, a rear door, and above one rear wheel.
>I'd like/need to sand off teh rust before applying touch-up
>paint and was wondering whether there is any danger of sanding
>off irreplaceable rust protection in those areas?
>
>TIA,
>-gbr
>
>
>