Types
of Car Paint and Auto Paint
Understanding the types of car paint available is
important to make sure you are using the best product for your
application. There is a lot of industry jargon used which is often
confusing at best and in some cases misleading. Our goal in this article
is to give some good details including pros and cons for the various types of
car paint products.
Undercoats
Undercoats are sometimes referred to as primers,
sealers, surfacers, or adhesion promoters which is a broad category
encompassing anti-corrosive primers, primer sealers, primer surfacers, and
adhesion promoters used in properly preparing the surface for color.
Undercoats serve a wide range of uses with varying types of chemistry involved.
Anti-Corrosive
Primers
Anti-Corrosive primer’s main function is to protect
the substrate (whatever is being painted) from degradation due
to the effects of corrosion. There are many types available each
with its own benefits.
2K (2K means 2 part) epoxy primer is an outstanding
choice for refinishing bare metal due to the excellent adhesion and corrosion
resistance imparted from the anti-corrosive polymers in a typical 2K epoxy
formulation. Epoxy primers often serve a dual purpose as a good sealer as
well.
Pros: Excellent
adhesion, and corrosion resistance. Adheres to a wide range of substrates.
Cons: Typically, does not sand or fill well compared to
surfacers, slow cure in cold conditions.
Self
Etching Primer
Self etching primer is a primer system which can be
one or two component and also provides very good
corrosion resistance and adhesion on a wide variety of substrates. These
primers are used extensively in auto collision repair due to their speed of
dry.
Pros: Very good
adhesion and corrosion resistance, fast dry even in cooler climates
Cons: low film build makes them useless for much fill or sanding,
corrosion resistance slightly less than 2K epoxy.
Enamel
Primer
Enamel primers cure by oxidation from the air and
can provide some useful benefits such as no pot life and no activator component
to measure and dose. Corrosion resistance can be quite good although
typically not as good as 2K epoxy.
Pros: good adhesion
and corrosion resistance, not pot life (unless activated), no isocyanates
(unless activated), typically inexpensive
Cons: can be sensitive to recoat (wrinkling).
Primer
Surfacers
Primer Surfacers ultimate role is to provide a
smooth surface by hiding hiding defects such as
scratches, gouges, chips, small dents, and the like. In general Primer
Surfacers are used over anti-corrosive primers since strong corrosion
resistance is not one of this category strong suits
They are typically sanded to a smooth surface ready for painting so the ability
to sand easily is important.
2K Polyurethane Primer Surfacers
2K Polyurethane primer surfacers or urethane filler
as they are also sometimes called are two component primers designed to fill
well and sand easily. These primers are the work horse for the collision
repair industry when fill and sanding is required. Urethane chemistry
ensures best durability and long-term performance for a
number of performance attributes.
Pros: High solids
for filling, greater long-term flexibility and durability, less shrinkage, good
sanding
Cons: higher cost than lacquer, contains isocyanates (health risk),
relatively short pot life, two parts to mix
Polyester
Primer
Polyester primer is sometimes referred to as spray
filler or sprayable bondo. It cures by reaction
of peroxide induced crosslinking of unsaturated polyester polymers. This
is a two-component product.
Pros: Very high
solids/Fill, typically lower sprayable cost than 2K urethane, low solvent
content.
Cons: much less flexible than urethane on average, activator
dosage can be inaccurate, can be hard to sand.
Lacquer
Primer
Lacquer primer dries by solvent evaporation
alone. This approach has been used for many years but has diminished
greatly since urethane primers offer much better system durability long term.
Pros: low cost,
fast dry, easy sanding.
Cons: tends to shrink, crack,
and check on long term exposure, high solvent content is bad for environment.
Primer
Sealers
The primary role of a primer sealer is to provide a
smooth non-porous foundation for color to be applied over. Primer sealers
typically are lower in viscosity to ensure a smooth application without
sanding. Primer sealers generally are not designed for good sanding
properties.
Two component polyurethane primer sealers have
become the choice for most painting professionals for sealing purposes due to
the durability, cure rate, and reduced recoat sensitivity versus enamel primer
sealers.
pros: excellent
durability, good cure response in cold weather, excellent gloss hold out,
reduced recoat sensitivity.
cons: two component pot life, higher cost than enamel,
contains isocyanates.
Many epoxy primers also double as a nice primer
sealer as well. However, epoxy should not be used as a sealer under
transparent or semi-transparent colors due to their instability to light
exposure.
pros: long pot
life, excellent adhesion/corrosion resistance.
cons: slower cure than 2K urethane, instability to light.
Enamel
Primer Sealer
Enamel primers have been used as sealers for
decades and dry by oxidative cure so no additional
activator is required... When properly formulated they offer great
sealing properties.
pros: low cost, no
activator required, good adhesion/corrosion.
cons: re-coat sensitivity can be a problem on many.
Adhesion
Promoters
Adhesion promoters is a category of undercoats
whose sole purpose is to ensure adhesion of subsequent layers to a give
surface. These are typically low in solids and often clear in nature.
Generally used to ensuring adhesion on paints to plastic substrates.
pros: adhesion
over plastic, commonly ready to spray.
cons: no fill, no corrosion resistance (not normally needed
on plastic), over application can be easily done.
Single
Stage
Single stage topcoats which are also known as, one
stage, monocoat, or direct gloss, reach their final
gloss without the use of clear coat. These finishes can vary greatly in
terms of gloss and other appearance factors. The durability performance
can also vary greatly depending on the chemistry used to achieve a cured paint
film. Knowing what kind of single stage, you are working with is critical
to know what to expect in terms of durability.
Alkyd
Enamels
Alkyd (pronounced AL-KID) enamels were among the
first paints ever used on automobiles. A large portion of the polymers that
make up the back bone of alkyd enamel paints are actually derived from natural
renewable resources which may be the only thing going for them now when
compared to modern single stage finishes. Alkyds cure by the reaction of
atmospheric oxygen to form a cured paint finish with varying gloss
levels. These finishes do not require an activator but an activator may
be used in most if improved durability is desired. Alkyd enamels are rarely
used for automotive coatings today.
pros:
No activator required, low cost, good flow and leveling, excellent flexibility.
cons: slow dry, poor durability, recoat sensitivity.
Acrylic
Modified Alkyd Enamels
Acrylic modified alkyd enamels most
commonly known as “acrylic enamels” now were a step up from alkyd
enamels where an acrylic polymer was grafted on to an alkyd to help improve
durability and dry time. Acrylic enamel does show improvements in that
area which makes it a viable product even in today’s automotive market.
Like alkyd enamels acrylic enamels typically can be used with or without
activator.
pros: no
activator required, low cost, good flow and leveling, reasonably fast dry.
cons: durability less than urethanes, flexibility
can be an issue, reloadability commonly an issue.
Nitrocellulose
(NC) Lacquer
Lacquers are a class of topcoats that dry by
solvent evaporation alone. These type finishes do not “cure” they simply
“dry”. Because of this they are said to be reversible meaning they can be
dissolved with the appropriate type of solvent. Nitrocellulose Lacquers
were early solutions to the slow dry of alkyd enamels for improving
productivity in automotive finishing. They typically dry very
quickly. However, the problems associated with Nitrocellulose lacquers
and the raw materials used to make them (NC polymers are extremely flammable)
eventually led to their demise for use in the automotive coatings
industry. Their use today is typically associated with the period correct
restoration of certain vintage vehicles.
pros: very
fast dry, easy to spray, no activator required.
cons: yellowing in many colors, poor flexibility led to
cracking and checking, fuel resistance vs. curing finishes.
Acrylic
Lacquer
Like NC lacquers acrylic lacquers feature fast
drying. However, the acrylic polymer back bone contributes to improved
lightfastness and gloss retention vs NC lacquers. Acrylic lacquers are
typically applied in many layers often with polishing between layers to get a
beautiful deep gloss finish that lasts…well a little while when used
outdoors. Acrylic lacquer was indeed an improvement over NC lacquer but
still does not have durability comparable to urethane single stages.
Acrylic lacquer is still used today by some for mainly for restoration of
vintage vehicles or those wanting to purchase something really
cheap.
pros: vary fast
dry, easy to spray, no activator required, usually very low cost.
cons: poor flex leads to cracking, fast gloss loss requires
constant polishing.
2K
Urethane Single Stage
Urethane or Polyurethane single stages are
relatively new on the auto paint scene although they have been around for
nearly 30 years now. Urethanes used in automotive finishes are said to be
“two components” because they require the use of an activator to cure the
film. Much of the technology was developed in Germany and the German term
for two component was shortened to “2K” which is often used to describe
them. There is a wide variety of urethanes on the market
but most used in automotive finishing are very durable and can make some
fantastic finishes. One of the few downsides of urethane’s is the fact
that the activator used in them is quite hazardous to your health so great care
must be taken to avoid exposure. However, with adequate exposure controls
and personal protective equipment painters handle these finishes constantly
with no problems. Another downside to urethanes is they have a pot life
meaning once mixed with activator there is a limited amount of time the mixture
is useful.
pros: most durable
single stage, high gloss, greater solids for deeper looking finishes.
cons: pot life, contains isocyanates which are harmful
while painting, cost is higher than other single stages.
BaseCoats
Basecoats also known as, base, or base color, are a
class of automotive paints that require a clear coating to achieve the final
gloss and appearance of the painted system. The process of applying a
basecoat color and then clear coating is known as a two stage or basecoat
clearcoat process. Basecoat and the basecoat/clearcoat process in general
was designed to improve upon certain weaknesses of single stage finishes.
As a general rule basecoats apply metallic and
pearlescent finishes more evenly and with more effect than single stage
finishes. Furthermore, basecoats tend to dry much faster and leave a lower film
build than single stage finishes making them more suited for multi-color and
graphic painting. Perhaps the greatest attribute of basecoat/clearcoat
systems is improved longevity. Properly used basecoat/clearcoat systems
hold gloss significantly longer than single stage finishes and require less
care and maintenance (less waxing and detailing) as the finish ages. This
was not always the case as early attempts on production cars had issues with
the clear coming off but today car manufacturers control production parameters
much better and rarely have issues with the clear coming off. In general,
base/clear finishes just perform better long term than single stage gloss
finishes. In fact, more than 90% of all cars rolling off the assembly
lines today are painted with a base/clear system even though applying
base/clear requires an additional step to reach the final finish. Auto
manufacturers incorporate this extra step in their process because thousands of
hours of performance testing have proven base/clear systems make their products
look better for longer than single stage paints. Some of the basic types
of basecoats used for repainting cars are listed below.
Urethane
Basecoats
Urethane basecoats use the strength of the urethane
linkage in molecules to build a tough yet flexible basecoat system. This
class of basecoats either requires the use of a small amount of catalyst
(usually 1-2 oz per quart or up to 5%) or the urethane linkages have been
pre-built into the resin system. Many of the brands known for “premier
quality” have utilized this approach to make high quality basecoats.
pros: durability
and toughness, excellent weathering, metallic/pearlescent control.
cons: sometimes an activator is required (depends on brand).
Polyester
Basecoats
Some brands also feature their basecoats as a
“polyester” basecoat. Polyester basecoats are formulated with special
polyester polymers that generally help with metallic and pearlescent
orientation. Depending on the type of polyester polymer used the solids
can be slightly higher than urethane basecoats which can be a pro and con in
some cases depending on what you are doing.
pros: slightly
higher solids vs urethane basecoat.
cons: often less durable than urethane basecoats.
Single
Stages Masquerading as Basecoat
Some manufacturers will recommend applying a
clearcoat over their single stage finish for added durability. This
approach does indeed improve the durability and depth of the single stage finish but you do not get a lot of the key advantages of the
base clear system. Single stage does not handle metallic and pearl as
well as base, single stage typically does not hide or cover as well as base,
and single stage does not offer the same rapid dry speed and low film build up
for quick and clean tape lines as basecoat. Some even offer a “basecoat
converter” for the single stage but this acts to dilute the pigment in the
single stage even further reducing coverage even more.
pros: cost is
sometimes less per gallon but often more in total job cost than a real
basecoat.
cons: lower coverage, slower dry, less metallic/pearl control than
true automotive basecoats.
MidCoats
Midcoats
are a class of auto paints that create a unique color effect by applying a
semi-transparent color layer over a base color layer. This approach is
sometimes referred to as a 3 coat or tri-stage process of generating
color. Truly unique colors can be generated in this manner. White
Pearl Tri-Coats, chameleon paints, and candy paints are all common examples of
this approach. As far as the chemistry is concerned most midcoats are either the same or similar chemistry as a
basecoat or a similar chemistry as a 2K clear or single stage. Often in custom
painting intercoat clear or 2K urethane clear is used
to deliver effect solids such as pearl powders, flakes, glow in the dark
powders and the like. While intercoat clear is
nearly always a midcoat, 2K clear is typically not
except when used to deliver effect solids. In some cases, you have a
choice between which type of midcoat you use and
knowing the various options will help you make the correct decision for your
situation.
Midcoats
from Basecoat Chemistry
The title sounds like a
oxymoron for sure but what we mean here is midcoats
created from the same chemistry as a basecoat. As you might expect you
get the same advantages from using a midcoat based on
base coat chemistry as you would from a base coat. When applying effect
solids such as pearls, and flakes you should always
consider a midcoat derived from basecoat chemistry
first. We also intercoat clear in this category
since well engineered intercoat clear is typically
the same chemistry as a basecoat. Chameleon paints, and white pearl midcoats are essentially exclusively built from base coat
chemistry. The orientation control and the pearl “flash” (measured as
flop index) effect are substantially higher with basecoat chemistry. When
we compare midcoats of basecoat chemistry vs midcoats of 2K chemistry this is what we see:
pros: better
orientation, faster dry, cleaner taping (less lip), better pearl flop,
resistant to lifting/wrinkling.
cons: less depth and build than 2K finishes, over
application is sensitive to cracking, adhesion problems.
Midcoats
from 2K Chemistry
Midcoats
built from 2K chemistry are less frequently used but still a noteworthy
category since 2K candy paints or tinted clears are categorized here which
represents a significant use of midcoat. The
depth of image and resistance to dye migration (bleed) are the main reason 2K
clear type chemistry has survived and flourished in the mid coat
category. Some painters also like to use 2K clear to apply their pearls
and flakes but professionals find intercoat
clear superior for this use unless you are using the “sprinkle” method of
applying metal flake which works better with a 2K clear since it is slower
drying than inter coat clear.
pros: more
film build = more depth of finish, greater resistance to dye bleed.
cons: more lifting/wrinkling potential, slower dry, less
control of pearls.
ClearCoats
Clear Coats is one of the most critical categories
for modern automotive finishes because it plays the largest role in determining
the final appearance and durability of a base clear system. There are many
options available for clearcoats on the market but knowing which is the right type to buy can be confusing. We will try
to cut to chase and offer some relevant information help you separate sales
hype from true performance.
Topcoat
Clears
Topcoat clears are simply clears that are intended
to be the final or “top” coat of paint applied in a base clear finishing
process. As the final coat performance factors such as gloss, depth of
image, flow and leveling, ease of polishing, resistance to scratching,
hardness, and longevity are some of the key factors a topcoat clear must
exhibit to be truly effective. While there have been many attempts from
other chemical types there is only one relevant chemistry for a topcoat clear
and that is 2K polyurethane clears. I know some people would argue 2K
urethane finishes are different but from a chemical standpoint a 2K urethane
does not exist rather they all belong in the same “poly” (meaning many) urethane
family. Lacquer clear is another type of topcoat clear that has been used
in the industry but its relatively ineffectiveness compared to 2K polyurethane
clears makes lacquer clear irrelevant for our discussions. While 2K
polyurethane chemistry may be the only relevant category for topcoat clears
there are variations within the chemistry and “sales hype” which we will
discuss in more detail below.
2K
Polyurethane MS Clears
MS refers to “Medium Solids” with solids
essentially being the amount of film left behind after the solvent evaporates
from the applied paint. This represents a wide category of clearcoats
encompassing most of the clearcoats available for sale in North America. A
simple “MS” description is actually a very broad description
so it is difficult to determine much about expectations from this simple
description/ If you are investigating a clear that has simply uses
“MS” as the description ask the supplier for more detailed information to
determine which of the following categories it best fits into.
Turbo,
Production, Speed or Spot Clears
You will see these terms used a lot to describe
clears that are designed to be polished and put back into service very quickly.
These clears are often used by collision repair facilities to improve production
through their facilities. These clears often require more polishing
to achieve that deep wet look gloss than the next type. However, once
polished they can and often do look just as good as Glamour Clears.
Glamour,
Overall, Wet Look or Show Car Clears
This class of clear is generally slower in drying
than the speed or production clears but this can be good as it allows for more
flow and leveling. The down side is that it also makes
them easier to sag or run and gives more time for dust, bugs, and the like to
land in the finish. Generally speaking, the “off
the gun gloss” (gloss before any buffing) is higher than the faster speed
clears. These clears also tend to be less moisture sensitive on drying
which can be a benefit to those with less-than-ideal air delivery systems.
HS
Clears
HS or “Higher Solids” Clears will contain more
resins and additives which in turn leaves a thicker film left behind after
solvent evaporation. This typically results in a deeper, higher gloss finish
than “MS” clears. The downsides to this class of clears is
that they can be a little harder to spray without orange peel or without
sagging or running. Like overall clears, HS clears tend to dry a little slower.
Because of the higher solids content JS clears are generally the most expensive
variety of clear as well.
Euro
Clears
Euro clears are clears that are reportedly based on
European technology which some companies advertise as better and thus charge
more for the “Euro” product. This term is mainly used for marketing purposes
and in our experience does not suggest a superior product by any means.
The technology used in the European automotive refinishing market is largely similar to that used in body shops across north
America. One difference we have noted is that body shops in Europe have a
higher percentage of shops using heat to accelerate drying. This might
suggest Euro clears on average have been better optimized for baking
conditions. However, there are many clears made in north America that are
very well suited for baking applications as well. As for durability
performance, there is no evidence to suggest that on average Euro clears
perform better on average than standard clears made in North America.
InterCoat
Clears & Jambing Clears
Intercoat
and Jambing clears are a special class of clears
typically not used as a final topcoat clear. Intercoat
clears are in most cases simply a clear version of the resin system used in
basecoat colors. This resin system provides the fast dry and
metallic/pearlescent orientation that true automotive basecoats are known
for. A clear version of this system is useful for application of effect
solids like pearls, flakes, and specialty powders. Being basecoat
chemistry, it also has good “tie-coat” properties to help adhesion of basecoats
to fresh coats of basecoats and clearcoat etc. This is particularly
useful in layering processes such as art work.
Jambing
clears are clears designed specifically for the purposes of painting door jambs
and other non-exposed vehicle areas where a fast-drying clear is useful so
doors and the like can be closed soon after application and prepared for
painting.
