Auto Detailing News Winter issue

A Little More You Should Know About Paint
SOLVENT POPPING
You’re not a painter, but do you know
what “solvent popping” is? Solvent popping
occurs when trapped solvent in the
paint expands arid breaks through the
applied paint film. Inside each solvent
kernel is moisture, add heat and the water
expands and blows it apart. The solvent
is like spheres, you can actually see
them embedded if you go down through
a dried paint film, especially a clear coat.
They reach different levels in the paint
film, and you cannot buff them out. If
you sand them, then you are left with the
problem of pin holing. Bottom-line, the
paint has to be removed and re-sprayed.
What types of things occur with solvent
popping? Here are just a couple:
Blistering: This describes bumps in
dried paint film that looks like small pimples
or bubbles. This can be caused by
moisture trapped in the paint film, insufficient
drying time after wet-sanding,
contamination in the air lines used by the
painter or even heavy humidity during
paint application.
Air Entrapment: This is relatively rare
in painting and can be caused by trapped
air pockets in the wet paint film. Having
the spray gun too close or moving the gun
too slowly while not having sufficient air
pressure can cause this problem. It usually
can be rubbed out.
Dust Contamination: This is not
as much a problem today because of the
implementation of dust-free paint booths.
The chief cause of the problems today include
the use of poor grade masking paper,
particles coming from inexpensive degrading
air lines, poor vehicle prep and a painter
with dirty work clothes. Dust particles
usually will rub out.
To best understand the concept of solvent
popping what I want to do is ask and
answer a few questions about solvent popping
that were presented and answered by
a number of automotive coatings experts.
• What is happening when
solvent popping occurs?
Simply, solvent in the paint is coming out. Solvent is the
medium used to spray the paint. And, the solvent has to
completely evaporate for the paint to cure or crosslink.
This does not happen when the solvent “pops.” What
happens is the top layer of the paint crosslinks with solvent
underneath. Later, when the solvent tries to evaporate,
that is to go from a liquid state to a gas, you have a
solvent pop. It is just like popcorn where there is moisture
inside of each kernel. Add heat and the water expands
inside the kernel and blows it apart. Paint does the same
thing, blowing the paint apart.
• What is the gas you speak of? Air?
No, it is solvent changing from a liquid to a gaseous state.
• Is the gas flammable?
Yes, but they would be better called combustible on a DOT
scale.
• So for the painter and/or the detailer this is
a bad problem?
Yes, without question because there is not a quick fix. Bottom
line, if solvent popping has occurred on a paint finish it
has to be removed and repainted.
• What actually causes solvent popping?
It can be a combination of things in the painting process.
The spray gun, the painter and what is called film buildtoo
much paint.
• So even if you have a paint booth, good
spray gun and an experienced painter, if
too much paint is applied you can have a
problem?
There also is the issue of the solvent chosen. If the painter
chooses too fast a solvent you are going to have problems.
The biggest problem is the painter’s unwillingness
to change, to do things the old way. You have atmospheric
changes depending on the season and you must adjust the
solvents. In the fall things dry too slowly and in the spring
is when you see solvent popping occur.
• I have heard that shop owners tell their
painters “don’t buy anymore solvent until you
use up what we have got in inventory.”
Is that a problem?
As mentioned, there is a variety of solvents in every paint
product. That means there will be a variety of evaporation
rates in the solvents used to manufacture the paint. If
the painter uses a fast reducer that does not mean that all
the solvent in the paint would be “fast evaporating.” There
also could be some slow evaporating solvent as well. As the
temperature increases, if you continue to add fast solvent
the top of the paint will form a film or skin over which
traps the slow evaporating solvent, and eventually you will
get solvent popping as this solvent tries to get out.
• Are paint companies trying to develop
products to reach the correct flow to avoid
painter error?
Yes! If the paint has to do things to adjust for poor chemistry
then there is trouble. Paint companies need to put out “idiot-proof
” paint, so to speak.
• Until those products come along what can
the painter do to prevent problems?
The paint shops and detailers should purchase the “solvent
package” that is designed for the paint. For example,
when we talk about a clear-coat we mean ready-to-spray.
Everything is there, paint, reducer, etc. We have designed
a package and have tested it in a variety of situations. We
know it works, if you use all the parts. Unfortunately, some
shop owners, in an effort to save money, will buy cheap
paint and cheap solvents. Some will buy good paint and
cheap solvents.
• You hear painters complain about the
quality of the paint. For example, “the car
was perfect last night but when I came in
this morning the hood, roof and deck were all
bubbled over.” What is this all about?
This was a problem with air dry lacquer primers and sealers,
but we don’t use these any longer. It can still occur,
however, where there is super high humidity, like in the
Southeast Coastal area in the late summer. What happens
here is the painter uses slow solvents because it is hot, but
with the humidity so high the solvents are even slower and
won’t come out. Then you have heat speeding up the cross
linking reaction.
24 | AUTO DETAILING NEWS | VOL. 5, NO. 4 • WINTER 2020