Hm. I've never seen advice here about paint issues, but it would be
nice.

I have the same problem with my old Sentra -- its pale bronze finish has
frosted-looking patches on the trunk and hood. Some guy told me that
will happen with a lot of metallic paints. But I can scrape it with a
fingernail and it's bronze underneath.

What's the truth?

Sorry, but the information included in the response I sent came from
my head.  The infomation was put there by multiple week long sessions
at schools offered by Dupont in Detroit, PPG here in the San Francisco
Bay Area, New United Motor Co., Chevrolet in San Leandro, California,
Ford Motor Company in Detroit, and of course "daddy" may have taught
me a thing or two after I was old enough to get out of the crib in the
office of the body shop he owned.  I painted my first item, my own
bicycle, before I was ten.  In fact, because our shop, like most shops
during the 50's--I may be older than you think--had many partial pints
and quarts of lacquer paint****(this reminds me_ pints and quarts_look
at the end of this response for an aside that connects us to
England)**** left over from repairs to customer's vehicles.  A kid, me
that is, should be able to use such material , not just let it spoil
from age.  So one week I painted my bicycle five different times using
five different colors.  It wound up blue metalic.  I painted my first
complete car when I was 15.  (If you want to hear that story ask!!!) I
have done body work on a car, belonging to a supply sargeant, on the
side of the road near Tombstone, Arizona, in 1964, to make a few extra
bucks when I was in the Army. (More funny stories)  I did the body
work with hammer and dolly, applied plastic auto body filler (bondo to
you), sanded it smooth with a 2x4 wrapped with sand paper. I  primed
and finish sanded the repair, BUT, sent the owner to the local
body\paint shop for the painting.  A quality technician or a quality
repair shop really does want the best that is possible for the price
they charge their customers.  I have been ICAR certificated--they give
out certificates after the class is attended--as a student, and an
instructor in Unibody Repair, Welding, Finish Matching, Steering and
Suspension, Plastic Welding and Repair,  Aluminum Vehicle Welding and
Repair, and I have taught ICAR classes of more than  one hundred
students-- pros in the auto collision industry.  I hold a lifetime
Teaching Credential in Auto Body Repair at the community college level
from the State Of California.  I have given one day and four-day
seminars to the owners of Miracle Auto Painting franchises from Calif.
to Texas.   I do other things too.

I'm sorry to bore you, but perhaps, if I say that painting is
something that requires preparation, then paint application;  my
background may lend support to belief.

Since this is the open internet, the present government administration
is snooping on anything and everything, identity theft is rampant, and
mostly because we just want to be left alone unless "we" want company,
I can understand you not wanting to submit your self to defamimation
lawsuits by mentioning where in the world you live that has absolutely
no quality repair shops.

I responded to your post because you sounded as if there is no hope
left for you in this paint world.  But there is, there is.  First, It
is possible for novices (newbies to you computer folk) to do the paint
steps that really guarantee that the paint will stay put where the
painter's spray gun applies it.  This is the bulk of the time that is
figured in by Mitchell Manuals and the other companies that figure out
the time required to do  auto body and paint related labor items.  If
you take an old, bent, dirt laden, scratch infested, wet mouldy fender
from a car  part recycle facility (wrecking yard) into your $100, 000
downdraft spray booth, you will find, after using a stop watch, that
it takes about six minutes, including suitable flash time (see my
origional post) to put three coats of color (base coat) on that
fender.  If anyone else is watching you do this, you may have to prove
that you do not need another session with your analyst, just this
week, and you may wonder why the official time to refinish that fender
is 2.2 hours.   It is the time to prepare for the painter that
sucks-up most of that 2.2 hours, or 2.2 times $120 here in San
Francisco (***San Fran***next time--see next parenthisis brackets). If
you have a cash flow problem, but are able to scratch that itch on
your leg you have most of the skills that you need to do the ncessary
preparation ("prep" from now on,  'cause it is less up-load time).
What is needed is a thorough understanding of the problem.  I have
four kids, two boys-two girls.  Any one of them could write this post,
so don't think that if female help is available, it cannot be
utilized.  There is a community college in California that has only
one student that has graduated with two Associate Degrees in Auto
Repair .  One in Auto Mechanics and one in Auto Body Repair.  And SHE
proudly displays them both at work. But enough advertising, now back
to our program.....

Problem:  Clear Coat Failure

Only cure, except selling the car, is :  1-Remove the clear coat , and
color coats if they have also lost adhesion.
2-Reprime all metal that is exposed by sanding off the clear and base
coats.  Use the primer to "fill" any low spots that occur in the
process. (Pickie, Pickie, Pickie)   3-Finish sand the primer you apply
with proper "grit" sand paper.  4-Mask (use "masking tape"  for this
step, Halloween items do not work as well) or remove any items that
you don't want the paint gun to spray with paint (usually the
windshield, at least, qualifys for this step--you may certainly add
more items if you wish--some folks don't add more, believe it or not).
5-Aim the paint spray gun at the car and pull the trigger at the right
times as you move the spray gun.  It is definitely eaiser to move the
paint gun than to move the car for this step.

Basically, that is all there is to fix your problem.

STUFF HE DIDN'T TELL YOU:  Environmental;  Fish do not like paint.
Sand with water, use a five gallon bucket, use warm water in winter,
cool water in summer ( this is so your hand does not freeze in
Detroit, or heat up too much in Needles or Yuma).  As you scratch the
itch on the paint that you want removed, occasionally dip the sand
paper ino the water bucket.  When the excess water flows down the side
of the car to ground level, the fish would love it if it does not make
the trip to their home.  Sand the car on a level concrete slab, if
possible, allow the water to evaporate, then sweep up the dry base
coat\clear coat stuff that is there, pastic bag it, deliver it to a
recycling station, or at the very least put it in the garbage in a
double bag.  (I am a tree hugger at heart, a fish lover when I dive in
the Pacific, but also a realist.  For years, paint shops have let
paint residue run down the drains in their floors--residue  from paint
that used ground lead to insure better coverage with fewer coats.  NOW
we know that lead is not healthy for children and other living things,
just like war!  Your car paint does not have lead in it, well, unless
it was painted in China lately.....  But keep the sanding sludge out
of the drain ditch, the gutter out front, and don't let the kids lick
the drive way.   IF YOU CAN.  I don't believe that any state has laws
that will cause the enforcement agents to look you up for sanding one
car, but how much effort does it take to sweep the drive way compared
to sanding that car???  Much like the ratio of prep versus applying
the paint to that fender you painted in your $100, 000 paint booth.

More Environmental:  Use plastic gloves to protect your pinkies, or
maybe your hands, safety glasses for your eyes, long sleeves for your
arms.  If you dry sand with a mechanical device--use a face mask for
dust.  Are these really necessary??  Well, I know a teacher that uses
all of these techniques when he works at home on his own cars--even
when no students or anyone else is around.  If you attend a Dupont
paint class  in Detroit, you will use safety glasses when you enter
the lab area , if  just to watch from far away.  I think that if you
are old enough to own a car, you can decide for yourself, although we
citizens are losing this freedom to choose our own protection limits.
But I had to mention these, didn't I? Check directions on any products
that you use.  Think about what is listed by the maker of the product.
All should say " To be used by trained professional personnel only,"
or their legal departments are not earning their money.   Minimum
advice is to not use any spray paint material in a closed area,
especially, acid etch primer.  Use it, but outdoors.  Painting in a
garage that has any device that has a gas pilot flame is not wise, and
is also not recommended by local fire departments.  Buy an
inexpensive, but reliable, disposable face mask that is stated usable
for paint and\or oganic vapor products.  It is the size of the holes
in the filter material that really matters.  A molecule of air is
smaller than a molecule of paint organic vapor.  Of course, you can
always hold your breath while applying the primer.  The reason for the
filtering device is that most of the paint products have items in them
that cause cancer, destroy brain cells, do nasty things to your liver
and spem count, and\or create breathing problems.  I may have failed
to mention a thing or two.  Just wanted to bring your attention to
those possibilities.  You might want to consider not spraying on a
windy day if your neighbors new Porsche Carrera is close to your drive
way.  That might be more expensive than a newer Sentra.

Wet Sand the vehicle using that scratching motion that you said you
could do--your arm will naturally tell you the proper length. Wet
sanding is using water as a lubricant and as a medium to remove
sanding sludge from the contact area of the sanded material and the
sand paper.  There is a type of sand paper that is made for this
process.  It is readily available at auto body supply businesses.  It
is usually called "wet or dry".   Buy sheet sand paper.  Fold the
sheet in half--bringing the ends of the long length together, and
crease the fold.  Tear the paper in half at the crease.  I suggest
that you fold the paper and press the fold a few times before you tear
the sandpaper.  (practice makes perfect)  This helps to end up with
two equal halves.   If you don't choose the correct way to fold at
first, you will recognize that you can not fold the sandpaper into
equal thirds that are about "hand size."  This half-sheet tri-folded
piece of sand paper dipped into that warm or cool bucket of water,
placed under your flat open hand is the machine that will do all the
work to remove the failed layer of clear coat.  NOW, choices!!   I
love choices.  Makes the day un-boring.  First, to help make what I
have just mentioned more simple, remember to ask the sand paper sales
person to show you how to fold the sand paper.  If the sales person
cannot demonstrate how to do this, don't buy the sand paper from this
person.  Would you visit a Dentist that could not demonstrate how to
brush your teeth?  I thought not!  Have the person that sells you the
sand paper also show you "sanding pads."  There are many types of
these made.  I like firm, not squishy, not hard, sanding pads that fit
under the hand, and are designed to accept that torn tri-folded
half-sheet of sand paper.  This type of pad will keep the sand paper
flat and working along the contact surface.  Your hand has fingers
that allow no pressure between them.  Inefficent.  The next time I
design a human, I must remember to add flat square fingers.....
Another type has one flat side and the other side round.  The sand
paper is held in place by nail like devices.  This item may be called
a sanding "block,"  is usually harder,  more expensive, and uses
another type of folding.  DID I MENTION THAT I AM AWARE OF THE COST OF
THINGS.  BUT THAT IS WHY WE ARE DOING THE SANDING AND PREP,  RIGHT??
Anyway, this flat and round sanding block is best used close to side
moldings or any place that is perpendicular to the metal surface.  The
hardness of this type of block allows you to apply pressure very close
to body moldings to leave sanding scratches there--very close to the
molding.   I suppose that this is the time to mention that PAINT
STICKS BY SHRINKING ON TO THE SANDING SCRATCHES as it dries.    We
call this condition, "mechanical" adhesion.  This is why after
priming, there is more sanding.  Also, this shrinking is what causes
sand scratches to appear after the paint has dried, IF AN INCORRECT
"GRIT" of sandpaper is used .

One good thing that you may not have considered is, that usually, the
sides of the vehicle only need to have sand scratches enough to
accomplish mechanical adhesion.  The U V light does not work directly
on the vertical side panels of the car.  Therefore, the clear does not
deteriorate in these locations.  Simply sand well enough to remove the
shine from the surface of the side panels and that is all that is
required.  

Consider that the car factories and paint shops both utilize "systems"
that use different materials, but are designed to work in the same
way.  The system starts at the bottom, creating adhesion to the metal.
A phosphate based acid etch product cleans the bare metal and leaves a
super thin layer attached to the steel.  This coating is made so that
the stickest stuff in the in the auto body repair kit, epoxy primer,
will cling like a second skin.  Base coat material is made to adhere
to the epoxy  primer.  Clear coat stuff is formulated to, you guessed
it, stick to the base coats.  Epoxy primer used by auto paint shops is
rich in zinc.  This is the start of rust prevention on the system.
Most nasty rust is caused by "galvanic" action.  Basically two
different metals in the same area when wet create a battery like
condition.  Pluses and minuses, and ions, and well, to be short with
this, this condition creates electrolysis, and creates rust.  Epoxy
primer is a two part-- mix it just before use-- you have maybe two
hours before your primer gun has jelly in it--type of product..  You
will not want to use this at home.   An acid etch primer will act
simularly to create the initial bond between the bare metal and the
base coat material.  The base coat sticks to the acid etch, and the
clear coat sticks to etc, etc.  You are an expert in this by now,
aren't you.  This is the primer you may want to use.  It is available
in spray cans.  It does, as it's name declares, contain an acid.  The
purpose of this primer is to eat away any microcopic rust on the
metal, etch the steel, leave the super thin coating , and apply a
protective coating that other coatings will adhere to.  

In a perfect world, you would start with one manufacturers product and
end with that manufacturers product on the top layer.  This is not a
perfect world, and all you really want is a car that will not rust,
retain the paint that is applied, and not be embarrasing.  And these
things for an acceptable price.  Therefore you will break the first
cardinal rule, and mix manufacturers' products.  You have only two
choices of material that you will need.  Acid base and\or "filler
primer."  You understand that the etching primer is a must, and is
applied before any other product is sprayed on the metal.  Otherwise,
nothing will adhere as well.  Filler primer is placed on top of the
etching primer to raise the level of the low spots that you sanded to
get out that scratch in the door.  Acid etch primer is not applied
over anything but bare metal, it will not stick to painted surfaces
well.  ( I know, what about the edge along the metal-paint
border?--Spray thin coats--) This fact means that you will need
another type of primer that is available in your area--it may be
different from San Fran, and I rarely use spray primer in cans to be
able to make a good recommendation.  Talk to your painter, and your
paint-sandpaper supplier to see what they recommend.  There may be a
good, bad, maybe choice here.  Lacquer is not as good as some other
choices, but may be better than an enamel primer.  Enamel is a tricky
material to use, it will flow down the fender before you know it,
takes too long to dry, is time sensitive to being recoated, is
difficult to sand as a fresh primer gone bad, and will cause
"wrinkling" if applied too thick.  Remember, that .008 " is the
maximum for all the coatings before cracking is near.  You may exceed
this and do well.  I have seen a factory fresh Ford van that had been
painted with eight layers of alternating base coat-clear coat.   The
factories have been known to repair scratches on new vehicles before
they leave the factory property.  But Eight times????  The van was a
year old, and had no outer evidence  to show the layers.  A stone chip
caused the owner to request the repair.  

Somewhere in here I must mention two things that will affect the
process.  Sandpaper grit or grade,  and painting technique.  In the
auto paint world sandpaper is measured in numbers.  The sanding grit
or the abrasive stuff used to wear away the old dead clear is labeled
according to roughness.  These grades of sandpaper may also be called
xxxgrit sandpaper (the xxx's were used instead of numbers for ease of
explanation.)  There is an american and a european system of sorting
sandpaper.  Those that spend Euros will get a numbered paper that has
a P at the end.  This will probably not be a concern to you, but now
you have a bit of trivia for the office party.  The range of sandpaper
numbers shops use can be from 16 grit to 6000 grit.  Your fingernail
will fit between the pieces of abrasive glued on 16 grit sanding
disks.  Think boulders, large rocks, or the size of the sand in
Carmel, Calif--out about 100 feet from shore.  In thirty feet of water
you can count the individual sand particles while you lay on top.  At
the other end of the scale, your fingernail might not know which side
of the paper to use to sand with....use the side that has no numbers.
You should only need 220 grit wet or dry, 320 grit wet or dry, 400
grit wet or dry, 600 grit wet or dry, and 1000 or 1200 wet or dry, or
just some of these.

If you have a piece of property that you want to landscape, you would
use a bulldozer first, right??  After the dozer leveled out the big
stuff, you would use a shovel.  Then a big rake, then a small rake,
you get the idea?  To eliminate wasting time, using 220 grit will
remove the bulk of the clear.  If you were a shop, you might chose
another grade that would be rougher or coaser.  And you would use a
machine.  But for us, we want to remove the clear without leaving a
really rough surface in the metal.  When you see that your paint needs
to have a bed of 600-1200 grit sand scratches to lay on you will
understand your job.  So, here it is....220 grit to remove most of the
bad paint, then 320 grit to remove some more of the bad paint and some
of the 220 grit scratches, then 400 grit to remove the 320 grit
scratches, 600 grit to wear some more then sand with the grade of
paper that the paint can wants.  Some where in here you apply the acid
etch, then the filler primer, sanding as per directions.  SEE,  I TOLD
YOU--THERE ARE NO SECRETS.  JUST WORK.  BUT YOU CAN DO IT.  I was
wet-sanding cars for completes and spot jobs early in life, so the
kids can help too.  Think about the first novel manuscript that was
written on a typewriter!!       Tom Sawyer.....

Now a word from our paint gun sponsor.  The paint can...   The proper
method of using a spray can can probably be best obtained from some
youth in New York, New York.  I have seen their stuff, and it is
good....Well, I didn't say that I approve, or that it was appropiate.
But since I don't personnaly know any of those artists, I will say
that you should: 1- Hold the spray nozzle about 12 inches away from
the surface.  Spray with a straight line aim, overlaping each stroke.
2-Spray light coats--this creates less flash time between coats of
primer.  3-Spray in an orderly fashion-think rectangle, think spray
quickly to maintain a wet edge on one line, then spray the next line
before it dries, think too much paint is worse than too little paint.
think multiple thin coats are better than fewer thick coats.
4-Painting in the shade is better than painting under the full sun,
but most things are possible.  The big secret here is to get some wet
acid etch on the bare steel some way.  Since we are probly going to
sand the acid etch a little, the primer does not have to look like a
Picasso Cubist original.

More important than what I say, are the words on the paint can and the
primer can.  I could never figure out why some painters thought their
methods were better than the guys that made the paint.  The painters
never did spend millions testing out their way to do the stuff........
By the way,  did you know that the final word on a paint formula comes
not from that multimillion dollar computer, but from the seven women
working in the lab.  They have no color blndness.....

When you do prime the metal surfaces, cover any  part of the Sentra
that does not need primer.  Including your neighbors Porsche.  It is
always easier to cover than remove paint from that part. You can use
blue masking tape, yellow, white, whatever, but remove the tape as
soon as possible.  Cleaning the glue left on surfaces after the sun
has heated it up can be a real chore.  An "orange" or citrus base
cleaner may be more useful than other products to remove the glue for
this mistake.  I think it may take less time to remove masking, then
remask,-- some times--, than to leave masking tape on for any length
of time in the sun.  Before "taping" machines were invented, the
covering medium was newspaper.  Clean the window, place the newspaper
on the window, pull masking tape along the edge of the newspaper, then
pull the newspaper\tape assembly away from the glass and apply it to
the areas you need to mask.  This is not recommended for top coats,
some times the little particles of paper are blown off  into the
paint.  Not good that, is it?  If you are going to pay $6000-$10,000
you will want the shop to use that specially treated clear-coat stuff.
Another choice is plastic drop cloths.  Cover the whole car, then cut
out the area that you are going to prime.  This is the professional
method, but they use a mill thickness that is higher than I have seen
in household drop cloths.  I paid 77 cents for drop cloths to cover
the kitchen floor before painting the wood work and trim this last
Thanksgiving.  AND we are trying to save costs.....  The other bad
part about not using newsprint is that you have to bring a book to
read during flash times.

A few words about other choices......   Paint sanding sludge will
follow the gravitational pull that nature puts on it.  Remember the
concrete slab subject earlier!  But also, it  goes down between the
edges of the fenders and the hood panel. (bonnet in England)  As it
follows this road it will deposit  dried dust inside the engine area.
Come to think of it, there is other dust in there already.  Also there
is dust and dirt under the car, around the wheel house areas, under
the doors, not to mention near the bumpers, etc.  If we are going to
be really critical, perhaps we should wash and or rinse the under side
and engine area shortly before pushing it at the poor painter.  Most
of the dust in a new paint job comes off the painter, or off the
underside of the vehicle.  Removing parts or masking--This is a time
versus dollars versus possible part breakage, versus quality issue. It
is best to have nothing at all on the car when you paint.  This leaves
an uninterupted sheet of water barrier and color to protect those
panels.  Paint flow is hard to get next to moldings, so that sheet is
not uninterupted.  But let us look closer.  If you have moldings on
the side of the car, they are attached with a strip of urethane foam
that has glue on both sides.  We may safely call this double-sided
tape,  yes?  Good.  Now, when you remove that side molding, you will
remove that tape.  Some of the tape will go with the car, some of the
tape will go with the molding.  If you have not won any lotterys
lately, and your luck is really bad,  it is possible that that
molding, which is doing just fine where it is,  will have hardened and
in the removal process--will break.  Can happen, has happened, will
happen again in the future.  In that case lets hope that Nissan has
one available in their regional warehouse, or in the back-up space in
L. A.  They are only required to keep unimportant--not smog
related--items around for five or ten years.  I know that purists will
want to remove and re-install, but folks this is a cheap job.  Er,
ahh, I mean cost effective.  Another little item, if you pull the
lights off prior to painting, are you legal for the road?  Where do
you pull the lights?  Where do you put then back on after??

Why didn't I ask this next question at the begining?    I mean,   if
you find that you don't answer yes, then all those corrections to my
typing I have made will have gone for naught!!!

Evaluate the cost of painting over the estimated expected life of the
engine, transmission, etc.  A $600 paint cost divided by five more
years is $120 per year, not counting gas price increases.  If the cost
is higher,  the math used is still the same.  Is the total cost and
the anual cost acceptable to you?   One thing that has not been
mentioned much, is the owner's love of the car.  If you really like
the car, then the age does't matter.   Does anyone want to buy a 1924
Chevy 4 door open Touring car?   Yeah!  See.

Many people do not have the ability, the eyesight or even the desire,
to judge if the prep technician masked the un-removable items really
close.  Some do not care if the removable items are left on and masked
(less expensive--also called cheaper), if this brings the cost into
their budget.  Quality is a decision of the owner.  Usually, a
production paint company-read long line of cars going one way into the
spray booth, then out the other side into the adjoining attached
infared lamp heated "oven"--will be less expensive than a collision
repair facility that makes it's profit more on metal repair types of
work than applying paint.  Some of these shops consider painting a
nusance, and paint only out of necessity.  The names of the production
shops near you may be Maaico, 1-Day-Paint-A-Car, Miracle Auto
Painting, or something else.  You have stated that none reach the
quality that you desire.  If what you have seen that has disappointed
you was not the final spraying, then perchance you may be willing to
do the prep, and find a willing paint shop to only apply the paint. Be
prepared for the paint shop to demand to use their regular material.
If you change their paint, you may create a bottleneck in their paint
line that would make helping you bad for them.  A small independent
collision repair facility (body shop to you), may be your best choice.

I hope that this information will help.  I will monitor occasionally
to check for response.  If I can offer more information, I will
if it is desired

e b

*****Aside topic****Pints and Quarts.

In English Pubs beer is ordered in pints and quarts.  Whenever a
disturbance ocurred or the patrons became unrully, the barkeep would
yell out "Mind your pints and quarts." This is where the term, "Mind
your P's and Q's" came from.
This info courtesy of Matilda of Australia

 On Thu, 24 Jan 2008 02:02:55 -0600, "DemoDisk" <packrat@nospam.com>
wrote: