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 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 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 it’s 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 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 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 categories 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 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 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 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.
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 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 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 (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 don’t 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, recoatability commonly an issue.
Nitrocellulose (NC) Lacquer
Lacquers are a class of topcoats that dry by solvent evaporation alone. These type finishes don’t “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.
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. Urethane’s used in automotive finishes are said to be “two component” 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 urethane’s 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 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 clearcoating 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 despite the fact that 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 has proven base/clear systems make their products look better for longer than single stage paints. Some of the basic types of basecoat used for repainting cars are listed below.
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).
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 futher 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 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 is 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.
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’ll try to cut to chase and offer some relevant information help you separate sales hype from true performance.
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 really 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 actually 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 referes 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 make 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 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 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.