In my 27 years in the industry, I’ve never
seen paint problems more infrequently than I do today. Massive,
critical paint failures are extremely rare in any shop that uses
a single brand of automotive finishes from start to finish. The
few times in the last couple of years that I’ve gone to look at
an entire job that "blew up" on the painter, the shop
was mixing brands of undercoats, catalysts and topcoats.
Of course, using a single brand doesn’t automatically
mean your paint jobs will be flawless. A lot depends on the painter
and the environment, and a few paint problems still plague us
all when weather and shop conditions change.
From a couple of feet away, three of these
plaguing problems look very similar. To the naked eye, solvent
popping, moisture blisters and fisheyes all look about the same
– like tiny holes in the paint. Since they look so similar, here
are some tips to help you tell them apart and to prevent them
from ruining your paint work.
Under a 30X microscope (which you can buy
at a hobby shop for $10), solvent popping looks like a miniature
volcano. The edges surrounding the hole in the paint film are
peeled back just like the top of a volcano. Like the molten rocks
inside the volcano that burst through the Earth’s crust in a huge
explosion, solvent that’s trapped inside a paint film that has
dried only on the very top layer will violently burst out into
This bursting happens when the top layer of
the paint film loses solvent and dries before the rest of the
solvent – trapped in the lower portion of the paint film – can
escape. If your solvent speed is just a little too fast, the bulk
of the solvent will escape, leaving just enough trapped solvent
to cause die back. If your solvent speed is way out of whack,
the bulk of the solvent will be trapped inside and popping is
inevitable, leaving little holes in the paint film. Solvent pop
is a more violent form of die back.
Paint dry speed is dependent on the temperature,
the humidity and the air movement past the vehicle.
- Hot temperatures cause paint solvents to evaporate quickly;
cold temperatures cause solvent to linger inside the paint film
for a long time – just long enough to cause runs and to fingerprint
the next day.
- Humidity’s effect on dry times varies with the temperature.
Hot, dry weather – such as in Arizona – causes the solvent to
flash off very fast. Cold, damp weather – such as in Iowa – causes
the solvent to remain inside the paint film.
- Air movement past the car has an enormous effect on dry times.
Just like blowing on her fingernail polish causes your female
friend’s nails to dry faster, blowing more air past the car will
rapidly suck out the solvent from the paint film.
Unless you can control these elements – shop temperature and humidity
– all year around, you’ll need to change solvent dry speeds to
suit changing shop conditions. Solvent popping generally happens
when the weather changes and the painter doesn’t add a slower
solvent. When in doubt about solvent speed, choose the slowest
solvent you can use without running the paint off onto the floor.
The solvent is too slow when it stays sticky long enough to collect
excess dirt and dust.
Though it’s also possible to create solvent popping by applying
the paint film too thick, the root cause of the solvent pop is
the same: The top layer of paint dried before the remainder of
the solvent could evaporate through the many coats of paint film,
and instead, punched its way out, leaving a hole in the finish.
Looking through the 30X battery microscope, you can see the edges
of moisture blisters aren’t peeled back like those in solvent
popping. Instead, these holes look like miniature craters with
smooth, round edges.
What causes these miniature craters? Water.
Water comes in three forms: solid, liquid and vapor. The difference
in form is the result of temperature changes. Successful paint
shops have long since done everything in their power to trap moisture
vapor in compressed-air lines before it reaches the paint job.
However, on very hot and humid days, many shop moisture traps
can be overwhelmed.
The result: The water is sprayed onto the car inside the paint
film. Once the paint begins to dry, the water droplets rise to
the top edge of the paint film and are incorporated into it. The
paint resin then glosses up and hardens while the water droplets
continue to evaporate, leaving behind empty pits.
Note: Clearcoats are particularly susceptible to a moisture-pitting
problem in hot, humid weather. If the pits are small enough, they
can often be color sanded out and polished back to a gloss.
If your shop has moisture running through its air lines, it’s
also possible to trap such a large amount of water inside the
paint film that the drops – rather than rising to the top edge
– are encapsulated inside the paint film. These water blisters
will bulge up after the paint dries, and when they’re pierced
with an ice pick, water will run out. If you have this much water
in your paint line, I’ll bet your air tools are rusted solid,
Final filters that screw onto the spray-gun air inlet are designed
to trap the last little bit of moisture that slips by the desiccant
drier or refrigerated air dryer, but they’re not a long-term solution
to a moisture problem.
These little holes in the paint film are the most difficult of
the three to diagnose and correct. Unlike solvent popping, which
is always caused by the top layer of paint drying too fast, and
moisture blisters, which are usually sprayed onto the car in the
compressed air, fisheyes can be caused by many different things.
The 30X microscope can help you identify fisheyes. Under such
magnification, it’s possible to see that these imperfections have
a tiny moat around them. Why? Because the paint film flowed around
the imperfection much like a river splits around a large rock
in a riverbed. The contamination that interrupted the paint flow
can come from many sources.
Here are some tips to try to identify the cause:
- When a customer calls with a fisheye problem, the first question
I ask is whether the fisheyes are on just the flats (hood, top
or decklid) or if they’re on the sides of the vehicle, too.
If the contamination is just on the flats and not the sides, my
best guess is that the contaminant blew or drifted into the booth
and settled on the car.
If the contamination had been in the air line, the paint or the
spray gun, the entire car would be plagued with fisheyes. Because
it’s not, it’s likely that something like tire dressing or diesel
smoke was sucked into the booth after the car was solvent wiped.
Conscientious cleaning with wax and grease remover is the surest
solution to prevent fisheyes in this case.
- If the fisheyes are all over the vehicle, they could have
come from the air line.
Worn air-compressor piston rings allow oil to be blown downstream,
which will definitely cause fisheyes. An oil coalescer is designed
to trap this oil, which is carried down the air lines on the back
of water droplets. When the effluent from your moisture trap is
white, the water has oil in it. Stopping these kinds of fisheyes
permanently will have to be done at the piston rings.
- If the entire car is covered with fisheyes, the spray gun
could also be the cause.
If your shop uses a gun washer, it’s possible that the cleaning
solvent is contaminated with something. In the early days of gun
washers, we had several dealership body shops whose gun washers
got contaminated when the mechanics washed out service parts,
such as a carburetor. The spray guns that were exposed to the
contamination had to be completely disassembled and cleaned to
remove the problem.
- If the fisheyes are on the entire vehicle, another cause could
be a sophisticated paint sealant/wax.
These products are often sold by new car dealers and can be very
difficult to remove when painting is necessary. The test for cleanliness
is to toss a cup of clean water on the part after you’ve cleaned
it. If the water sheets off, the part is clean; if the water beads
up, the part isn’t clean and you must reclean it with something
that will dissolve the paint sealant.
I generally recommend that our customers try their regular solvent-based
wax and grease remover first. If water still beads up, we have
them try an alcohol-based wax and grease remover. The trick is
to find something that will break the bond the sealant has to
the paint. If neither type of wax and grease remover works, we
have the painters try a mixture of very hot water and laundry
detergent. Sometimes the same enzymes in the laundry soap that
remove your tough stains will also break the sealant’s bond to
the paint. Once the test cup of water sheets off, wipe the panel
with regular wax and grease remover to pick up any soap film the
detergent may have left behind.
When the fisheyes in your shop come and go, finding the source
is a true challenge; it’s actually easier to solve a fisheye problem
if the shop has them in all the paint work.
We’ve had our best success when we made charts listing every variable
for a given paint job, including which painter, which spray gun,
which air line, what make of car, which undercoats, which solvents,
what color, what time of day, what day of the week, etc. Although
no painter wants to play 20 questions every time something needs
to be painted – it takes way too much time – it’s your only chance
to find and correct randomly occurring fisheyes.
Tending to Tiny Holes
Simply using a single brand of paint products won’t guarantee
flawless finishes. You must also take into consideration the painter
and the shop conditions.
Hopefully, your shop continuously changes solvent speeds to keep
in tune with the weather and never has solvent popping in you
finishes. Likewise, if you install the right equipment to dry
the compressed air and you maintain it carefully, your chance
of seeing the tiny moisture holes in your paint work are pretty
slim. Unfortunately, tiny holes that result from fisheyes are
hard to prevent.
Whatever their cause, don’t let the size of these holes fool you.
They may be tiny, but their effects on your bottom line can be
Mark Clark, owner of Clark Supply Corporation in Waterloo,
Iowa, is a contributing editor to BodyShop Business.
Check it Out
To the naked eye, solvent popping, moisture blisters and fisheyes
all look about the same – like tiny holes in the paint. But it’s
important to tell them apart to cure them.
- Solvent popping looks like a miniature volcano, with the edges
surrounding the hole in the paint film peeled back. Solvent popping
occurs when the top layer of the paint film loses solvent and
dries before the rest of the solvent – trapped in the lower portion
of the paint film – can escape. Solvent popping generally happens
when the weather changes and the painter doesn’t add a slower
- Moisture blisters look like miniature craters with smooth,
round edges and are caused when water is sprayed onto the car
inside the paint film. Once the paint begins to dry, the water
droplets rise to the top edge of the paint film and are incorporated
in it. The paint resin then glosses up and hardens while the water
droplets continue to evaporate, leaving behind empty pits.
- Fisheyes – which have tiny moats around them – are the most
difficult to diagnose and correct because they can be caused by
many different things. If the fisheyes are just on the flats of
the vehicle, the contaminant probably blew or drifted into the
booth and settled on the car; if the contamination had been in
the air line, the paint or the spray gun, the entire car would
be plagued with fisheyes.