Date sent:        7 Dec 1995 22:38:14 U
From:             "Beck Carl J" 

Subject:             Re: Clear Coat Checking

"Al Powell" writes:

> A question for those of you attuned to paint work:  my 83 ZXT has 
> some places between the T-tops and on the tops of the door panels 
> where the clear coat is turning cloudy/chalky.  It is not flaking 
> off.  
> I've tried using extra (NON-abrasive) wax on these areas to provide 
> as much protection as possible....but it's slowly getting worse.
> Anyone have ideas/suggestions on how to at least arrest this 
> process??  I fear the clear coat cannot be returned to transparency.

Hi Al:
In 1972/3 I worked for a BMW dealership, then in 74/5 for Datsun, then it 75/6
for Volkswag.  All of them had problems with Clear Coat paint jobs here in the
southern U.S.  We had to re-paint one year old BMW's...

The problem (according to BMW and most of the paint mfg.'s) had to do with two
factors. UV Damage from the intense sun in the South.  And a difference in the 
coeffiecient of expansion between the clear coat and color coat.

The sunlight passes through the clear coat, and heats up the color coat, which
in turn expands.  The clear coat then "cracks"....

This is not as much a problem with newer paints as the coeffiecient of
expansion is more closely matched between color coat and clear coat,  and there
is some UV protection built into them.  But even so in the early 80's Clear
Coat Metalic paints still weren't to good in the Sunny South.

One method that helps delay this problem, if you repaint the car, that the
shops use here is - spray the color coat (usually with some type of metalic
flakes) on the car, then  mix the color coat paint (without the metalic) with a
little clear coat and apply that, then apply the final clear coat on top of
that...(usually we are talking about acrylic enamals or acrylic lacquers with
metal flakes as the paint type of discussion here).

This method distributes the heat more evenly, and gives the clear coat a chance
to heat up along with the color coats.

Anyway - once it starts, it keeps getting worse...strip the car and repaint.

BTW - waxing these type of paints, actually helps seal the heat in the color
coat....and helps to accelerate the cracking process...any of these types of
paint jobs are better served by a "poly" based sealer/glaze/protectant..
Carl Beck
Clearwater FL
IZCC#260 & IZCOOR#002