thecrazygreek
A.K.A. TheCraftyGreek
While peroozing the web I came across this nice write up. It has some good general info on auto paint with the pros and cons of each.
Enjoy!
undercoats
single stage
basecoats
UNDERCOATS
Undercoats are sometimes referred to as also known as primers, sealers, surfacers, or adhesion promoters 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 it's own benefits.
2K Epoxy Primer
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, corrsion 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 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
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-pourous 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.
2K Polyurethane Primer Sealer
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, excellent gloss hold out, reduced recoat sensitivity
cons: two component pot life, higher cost, contains isocyanates
2K Epoxy Primer Sealer
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: recoat 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 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, flexbility 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
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 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 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 urethanes 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 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
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 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
Enjoy!
undercoats
single stage
basecoats
UNDERCOATS
Undercoats are sometimes referred to as also known as primers, sealers, surfacers, or adhesion promoters 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 it's own benefits.
2K Epoxy Primer
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, corrsion 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 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
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-pourous 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.
2K Polyurethane Primer Sealer
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, excellent gloss hold out, reduced recoat sensitivity
cons: two component pot life, higher cost, contains isocyanates
2K Epoxy Primer Sealer
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: recoat 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 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, flexbility 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
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 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 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 urethanes 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 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
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 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
