In most cases, paint peels around the
windshield molding, the door handles or other areas that are difficult
to clean or sand properly.
In a business that pays you more for going
faster, it’s tempting to skip steps and "save" time.
As with many paint problems, there’s always time to do it over
but never time to do it right the first time. Though some preparation
is time consuming, it’s essential to obtaining a lasting, quality
finish.
To avoid another case of topcoat peeling,
check out the following steps. A little extra time spent in preparation
will save time in redos.
Step 1
The first step in preventing paint from peeling
is to have a clean surface. Often, areas that peel are the ones
that are hard to clean. By taking a little extra time to make
sure the surface is thoroughly clean before sanding, you
can prevent many adhesion problems.
There are two kinds of adhesion: chemical
and mechanical. To obtain a strong chemical adhesion, you need
a clean surface and a compatible topcoat applied in the correct
time frame. Miss any of these three criteria, and you won’t have
good adhesion.
Mechanical adhesion is nothing more than sanding
or abrading the surface to give the topcoat more area to adhere
to. Sanding almost doubles the mating surface because you now
have the additional surface area down one side of the scratch
and up the other side. Paint peels when it can’t hold onto the
substrate, so the more surface contact, the better the adhesion.
To ensure good chemical adhesion, make sure
the new finish gets good contact with the old one. If the old
surface is still covered with wax or paint sealant, the new finish
may stick to the wax. But, as soon as the wax lets go, the new
topcoat will come off with it. Wax and grease removers are solvents
designed to break loose the surface contamination from the old
finish. Lacquer thinners or enamel reducers tend to smear the
contaminant on the surface, but real wax and grease removers are
designed to float the road goo on top of the solvent. If you wipe
off the surface with a clean rag while it’s still wet, the goo
will come off cleanly.
Often, a poorly cleaned surface still looks
slimy. This is your clue that the first step – cleaning the surface
– isn’t done. However, there are times when the surface may look
clean, but the new finish will still peel off a few months later.
To be certain the old surface is really clean, toss a cup of water
on the recently cleaned area. If the water sheets off, the surface
is likely clean enough to sand. If the water beads up, the surface
isn’t clean and more work will have to be done before you begin
sanding.
If your original petroleum-base wax-and-grease
remover didn’t work, try wiping the surface again with an alcohol-base
solvent. If that doesn’t get the cup of water to sheet off, scrub
the surface with a mixture of hot water and laundry detergent.
The
trick is to find something that will break
the bond that the wax or road film has with the old finish.
Step 2
Once the surface is clean, abrade the old
finish to remove the gloss and increase the surface area. There’s
no substitute for a thorough sanding with sandpaper.
Many painters claim they don’t get paid enough
to sand everything with sandpaper, so they scuff the old finish
with something that works faster. Steel wool isn’t as popular
as it was years ago, but it still conforms itself well to odd-shaped
areas and serves to scratch up the finish in fine style. If you
use this method, make sure you blow off the shreds of metal left
behind before you paint, and remember to wear eye protection.
Another option is abrasive-encrusted scuff
pads, which come in several grades and colors. Most often, the
red-colored pads are coarser than the gray/green pads. In either
case, the depth of the scratch in the old finish is dependent
on how hard the tech pushes down on the pad. Using the same red
scuff pad, it’s possible to create a scratch that’s as coarse
as 220 grit or as fine as 400 grit. The difference comes from
the downward force on the pad. As you apply more pressure, more
encrusted abrasive is forced into the surface. Other abrasives,
like flap wheels or fiberglass-strand pens, also work well to
scratch up the old surface.
In many peeling incidents, the problem area
was neither sanded nor scuffed. The painter was in too big a hurry
and painted right over an unabraded finish. Not surprisingly,
when the new finish was chipped, the broken edge had nothing to
hold onto and gave way, little by little.
If your techs complain they can’t get the
vehicle completely sanded in the time allowed, make it easier
for them to do the job quickly. Buy special tools and sanders
that will make it fast and easy for them to sand the entire old
finish. With the huge variety of power sanders and specially shaped
sanding blocks available, there’s no reason your techs can’t get
in every crevice found on a car.
Step 3
If the surface is clean and thoroughly sanded,
about the only other cause for peeling finishes is a compatibility
problem. The easiest way to prevent this is to use paint products
from one manufacturer.
In an effort to match the durability of OEM
finishes, paint chemistry has gotten very complicated. Paint manufacturers
can’t worry about whether their products work with another paint
manufacturer’s.
"But," says the unconvinced shop
owner, "we painted the last three cars using Brand X clear
over Brand Y basecoat, and it worked fine."
My answer: You were lucky the last three times.
Sooner or later, your luck will run out.
Who will this shop owner turn to when an application
problem arises? The Brand X manufacturer isn’t interested when
you’ve used Brand Y color. Vise versa, the nice folks who made
Brand Y aren’t going to be surprised that the Brand X stuff didn’t
work.
By choosing products within one brand of finishes,
many potential peeling problems can be prevented. However, you
must still adhere to a time schedule. Suppose your shop painted
the Brand X basecoat on Monday but didn’t get around to applying
the correct Brand X clear until Thursday. The car left the shop
looking OK, but the customer is back in just a few weeks because
the rock chips on the leading edge of the hood are turning into
gigantic peeling spots. The problem: the time between color and
clear (or sealer and color or primer and sealer, etc.). Using
the correct products from one manufacturer helps, but the painter
still has to follow the directions for those products.
Other Causes
If the customer is back within six months
with a peeling finish, look to one of the above as the cause.
If the car returns sometime after six months with a peeling clearcoat,
check for a thickness problem.
If the clearcoat is too thin, the UV rays
of the sun will shine through the clearcoat and oxidize the base
color. The UV rays will literally eat the basecoat resin (which
has no UV screener in it), causing it to powder right where it
meets the clearcoat. No finish sticks very well to powder, and
the clear is no exception.
How did the clearcoat get too thin? Most likely,
it was sanded and buffed to get the dirt out. If you plan to give
the finish a thorough sand and buff, make sure to spray an extra
coat of clear just to feed to the buffer. As any painter can tell
you, there’s a big difference between a quick scuff-n-buff on
the hood and a total wet sand and polish to remove a farm-field
worth of dirt from the car.
Several vehicle manufacturers recommend that
you remove no more than 0.3 mil of clear, or durability will be
affected. If you sprayed two coats of high-solids clear and filled
the job with dirt or orange peel, you may have to remove more
than 1 mil of clear to get the job deliverably smooth. If you
know you’ll have a dirt problem, spray a third coat of high-solids
clear. That way, when you’re done with a hefty sand and buff,
there will still be a thick enough coat of clear to withstand
UV rays.
An Ounce of Preparation
Though peeling of the finish is one of the
most common paint-shop problems, it’s the absolute easiest problem
to prevent. Make sure the part to be painted is clean and sanded,
and when painting, use one brand of finish and apply it according
to the manufacturer’s directions. Remember: An ounce of preparation
is worth a day of redos.
Mark Clark, owner of Clark Supply Corporation
in Waterloo, Iowa, is a contributing editor to BodyShop Business.
Check It Out
A prevalent problem in paint shops across
the country, topcoat peeling can easily be prevented.
- Often, areas that peel are ones that are hard to clean. By
taking a little extra time to make sure the surface is thoroughly
clean before sanding, you can prevent many adhesion problems. - There are two kinds of adhesion: chemical and mechanical.
To obtain a strong chemical adhesion, you need a clean surface
and a compatible topcoat applied in the correct time frame. Mechanical
adhesion is nothing more than sanding or abrading the surface
to give the topcoat more area to adhere to. - To be certain the old surface is really clean, toss a cup
of water on the recently cleaned area. If the water sheets off,
the surface is likely clean enough to sand. If the water beads
up, the surface isn’t clean and more work will have to be done
before you begin sanding. - Once the surface is clean, abrade the old finish. There’s
no substitute for a thorough sanding with sandpaper. - Another sanding option is abrasive-encrusted scuff pads, which
come in several grades and colors. Other abrasives, like flap
wheels or fiberglass-strand pens, also work well to scratch up
the old surface. - If the surface is clean and thoroughly sanded, about the only
other cause for peeling finishes is a compatibility problem. The
easiest way to prevent this is to use paint products from one
manufacturer and to follow the manufacturer’s application directions. - If the car returns sometime after six months with a peeling
clearcoat, check for a thickness problem. If the clearcoat is
too thin, the sun’s UV rays will shine through the clear and oxidize
the base color, causing it to powder. If you plan to give the
finish a thorough sand and buff, make sure to spray an extra coat
of clear just to feed to the buffer.
Take a Closer Look
Paint chips when hit by a rock, period. Even the most durable
of finishes will chip if you throw gravel at it long enough. The
problem turns from chipping to peeling when the broken edge of
the topcoat doesn’t have a good hold on the old finish.
One of the best ways to tell if the old finish was indeed abraded
is to look at the peeling area with a 30X-power microscope, which
is AA-battery powered and available at many hobby or electronic
shops for about $10. One look through the microscope will tell
you if the old finish was sanded. It will also show if there’s
primer or sealer sprayed on under the topcoat.
