From: Dave Shaeffer [shaeff_d@bellsouth.net]
Sent: Friday, June 14, 2002 10:35 AM
To: 928
Subject: [928] RE: Keith's paint resto project.

Guys, gals, and others ....
My best advise (and I guess we all know what that's worth) is to determine
the total paint thickness _before_ using any abrasive compounds and/or
electric/pneumatic polishers. If the car is clearcoated and you remove too
much clear coat, you'll find your shiny "new" paint won't be that way very
much longer. If it's not clearcoated, you can easily find yourself looking
at a leopard-print paint job done in primer and whatever color it _was_. As
I've said before (seems like at least a million and a half times), the
typical factory paint job (including primers, color, and clear if used) is
only 5-6 mils (0.005-0.006") thick.

Some basic info/risk assessment/paint "repair":

If total paint thickness is between 2-3.5 mills:
Ether the primer is about to show or, if clear coated, the clear is nearly
gone. Using any abrasives can be disastrous. If the paint is in fairly good
shape (no deep scratches/gouges, excessively faded spots, etc.) the best bet
is just to keep it waxed with a high quality, non-abrasive wax, limit
exposure to sun and harsh elements, and you should get several more years of
life out of it. If you simply can't live with that, then the next best thing
to do is have 1.5-2 mils of urethane clearcoat shot over it. This will give
you several years of good looks before you must repaint.

If total paint thickness is between 3.5-5.5 mils:
This is the normal thickness range for most factory paint jobs, and you
should be able to "finesse" minor defects out, but if you're too aggressive,
you can still easily ruin the paint.

If total paint thickness is between 5.5-7.5 mils:
This still may be a factory job (some cars are repainted at the factory or
the dealer prior to shipment/sale), but you need to look carefully for signs
of a repaint. Overspray, tape lines in the door jams, etc. However, if it's
a repaint over the old paint, care must still be used, as unless you can
determine exactly how thick the new color/clear coat is, you can go right
through it to the old paint.

If total paint thickness is between 7.5-9.5 mils:
You're almost certainly looking at repaint. If the car was painted with a
quality base/clear system, or garaged, or "living" up north, it may last
several years before needing to be stripped and repainted. Again, if you
cannot determine the thickness of the "new" paint over the old, proceed with
caution.

 If total paint thickness is between 9.5-12.5 mils:
Generally you're looking at a car that has at least _3_ paint jobs, one on
top of the other. At this point, you'd be wise to ask what went wrong with
the first and second paint jobs, and what's really underneath all that
paint. Again, if it's garaged, and exposure to sun/the elements are limited,
it may last several years, but cracking/peeling/flaking are very likely, as
is a total strip and repaint.

If total paint thickness is over 13 mils:
Get your compressor in shape, and clean your paint gun. You have my
sympathy.

Paint thickness gauge:
Get one. I find it a bit amusing that folks will think nothing of spending
lots of money on "special" tools so they can save money doing their own
wrenching, but when it comes to the next most expensive (after a motor or
tranny) part of their car (a good paint job, some times worth more than the
car itself), they balk a spending a few hundred bucks on a good paint
thickness gauge that, with a bit of time, effort, and research, could save
them _thousands_ of dollars, lots of time, and much heartache. Go figure. :)
The gauges can range in price from $20.00 to $1500.00 or more. A good
digital can be had for under $400.00. Of course, as they depend on
electromagnetics to measure the thickness, they won't work on the aluminum
panels of the 928, but the readings of the steel panels will give you an
accurate reference for the rest of the car. But, if you have a small piece
of steel of a known thickness you can hold to the underside of an aluminum
panel, you can (using a bit of basic math) still determine paint thickness
using a gauge. ;)

However, be aware that the hood, tops of the fenders, roof (and all other
horizontal panels) do degrade sooner than other parts of the car, as they
are exposed more directly and more consistently to UV, and other harmful
elements, so keep that in mind when taking any readings and/or doing any
"finessing" on the paint.

Damage, what to do:
Cleaning/inspection. Thoroughly wash, rinse and dry the car. Inspect the car
panel by panel. If the defects appear as though they're on the surface, try
rubbing them with a bug/tar remover. Try any/all solvents on a hidden area
first. If the solvent fails to remove the problem, next step is a fine
polish. If the defect seems "crusty" or "corroded" (as is the case with acid
rain type damage) first prep the area with a "glass" brush (this is a
pen/pencil-like device with a bundle of glass fibers in place of the lead),
this can even be used to remove small amounts of rust. Once the area is
clean, take a few measurements inside the damaged area using a thickness
gauge (Groits and other such place have these. Price varies with quality),
record the readings, then take several readings of the surrounding area. If
the damage is only a few tenths of a mil and the surrounding paint is thick
enough, then finessing should work. If any of the defects are deeper, you
may not want to try removing them totally. Deeper defects will look better
if the surrounding paint is taken down a few tenths (if the paint is thick
enough to do so) so there will be less  of a "dip". If the defect is very
small in diameter, then touch-up paint may be the best bet.

Sanding:
If the defect is larger, or needs more work, than the next step is sanding.
Always use the finest grit that will remove the defect. I'd suggest starting
with 2000 grit. You can always go heavier, but if you start too heavy, you
can't go back. Why use super-fine paper and elbow grease when you can do it
in 1/4 of the time with a buffer ??? CONTROL. A few tenths (of a thousandth)
can mean the difference between fixing a defect and having to repaint the
car or an entire panel. Even 1000 grit or a buffer with a "no-cut" compound
can remove a lot of paint in short order. Always use a sanding block (size,
shape and "hardness" will be determined by the size and location of the
defect), as using your hand/fingers can/will leave "ruts" due to the
pressure of your fingers. Even though these ruts may be shallow and
"invisible", in direct sunlight and/or fluorescent lighting, they'll stand
out like the Grand Canyon. It's best to wet-sand (use a drop or two of dish
liquid in the water, as this also helps keep the paper from loading up), as
it keeps the paper from loading up with paint, and helps wash away paint and
grit from the paper with can add more scratches. Sand in one direction only
(I'll explain later), rinse the paper and the defect area often, and use a
second rubber block to squeegee clear the area every minute or two. This
allows you to better access the progress, as the remaining defect shows up
as shinier areas. Also, it's best to do this (or any paint/polish work)
under fluorescent lighting as it this shows any defects much better than
incandescent lighting. If you're not set up with good fluorescent lighting,
the natural sunlight is the next best thing. When you're ready to change the
paper, save the old piece (wash and rinse thoroughly), as a worn piece of,
say 600 grit, can become finer than a fresh piece of 2000 grit, and piece of
worn 2000 grit can become an ultra-fine 6000 grit.

Polishing:
Once as much of the defect as possible is removed via sanding, than it's
time to polish to bring back the shine. If the last grit you used for
sanding was 2000, you may be able to get away with using only one type
("grit") of polish/cleaner. It's best to do any polishing inside, as
sand/dirt is easily blown onto the car by even the slightest breeze. Also,
if possible, wet the floor before polishing to keep the dust/grit to a
minimum. If you are going to polish by hand (strongly recommend unless you
have a great deal of experience running a buffer on fine automotive
finishes, regardless of what the guys selling the buffers tell you), or have
a dark color paint, then you're probably going to end up using two steps for
the polishing phase.

The cloth:
The best bet is 100% cotton (clean and sand/grit free, or course). Be aware
that any synthetics (like nylon, rayon, dacron, etc) will scratch your
paint, so remove any and all stitching/binding unless you're 100% sure it's
cotton thread. Some of the new "micro-fibers" advertised may be O.K., but I
have no first-hand experience with them.

The Polish(es):
Too bad the manufactures don't have any standards regarding rating/grading
the abrasives ("grit") of polishing compounds as they do for sandpaper, so
the following is based on personal experience. For hand polishing, I use
"Blue Coral Liquid Fine Polishing Compound", followed by "Meguiar's Heavy
Duty Car Cleaner Wax". Again, if the last grit you used for the sanding step
was 2000, then it's unlikely that any sanding marks/scratches will be
visible after polishing. If you still have a bit of dullness or cloudiness,
then a coarser polish will be needed, followed by the wax. Polish 90 degrees
from the direction in which you sanded, this will show you the level at
which any scratches remain.

Hope this is/was some help to anyone considering a bit of paint "finessing"
...

Best regards,
Dave