The adoption of basecoat-clearcoat finishes by OEMs in the early 1980s represented a striking advance over single-stage color systems. By providing a coating over the base color, the clearcoat offered superior gloss, protection against color fade due to the sun’s damaging ultraviolet rays, and enhanced appearance, scratch resistance, and overall durability. Today’s clearcoats do all that better than ever.
Like all refinish coatings, clearcoats have made significant strides in advanced resin technology. Current clearcoats are compatible with waterborne basecoats and are a key part of innovative waterborne paint systems. These new clearcoats have been engineered to ensure easy use, generate superior productivity, and yield consistent high-level results.
Today’s range of clearcoat options covers all types of jobs that collision centers encounter. Our PPG clearcoat lineup, for example, includes air-dry express clears, quick bake options for production shops, as well as ‘glamour’ clears for the ultimate in a high-gloss, UV-protected finish.
Whether you work in a high-volume, production-oriented collision repair facility or a custom-focused restoration business, choosing the right clearcoat is critical for meeting the requirements of each job and customers’ expectations. To select the appropriate clearcoat for your situation, it is imperative to have a basic understanding of clearcoat technology, its role in providing a quality finish, and the key factors to consider in making the right choice.
The Chemistry
Refinish clearcoats are derived from acrylic resin technology. They are cross-linked with an isocyanate hardener to form a durable polyurethane film. Several chemistries go into a clearcoat:
- Resin — The resin is the foundation of any clearcoat and plays a significant role in how it sprays, how fast it cures, its hardness, its VOC content, and its overall durability. Since the resin is designed to be cross-linked with an isocyanate hardener, correct mix ratio is critical to achieving the proper reaction. Mixed improperly it can create a host of problems. And, when spraying any paint product containing isocyanate, it is essential to wear the proper respirator and safety equipment.
- Additives — Clearcoat performance is enhanced through additives in several ways. Additives can improve the atomization of the liquid to make it easier to apply and achieve better overall appearance with less orange peel. Additives can also affect how the clearcoat lays down—its flow and leveling characteristics.
- Catalysts — Added in very small amounts, catalysts speed up the reaction between the resin and the isocyanate hardener. The faster reaction, however, can shorten the clearcoat’s pot life and limit the window of time in which to spray it.
The keys to durability
The chief elements that contribute to a clearcoat’s durability are UV absorbers and film build.
UV additives absorb damaging ultraviolet rays, much like sun block for your skin. However, UV protectants alone cannot do the job to ensure durability.
Film build is critical
Film build is equally important to ensure long-term durability of the finish. It provides an important physical barrier to outside elements, including moisture and UV light.
Too low a film build can lead to premature film failure, dieback, and overall poor appearance. Too high a film build can lead to solvent pop, dieback, and even potential adhesion failure.
A final film build in the range of 2.0–2.5 mils is commonly recommended. Whether using a value or premium clearcoat, a film build below 2.0 mils will decrease durability. Before spraying any clearcoat on a job for the first time, measure film build on a test panel. This will help gauge how your application techniques affect the final film thickness. Two coats should suffice in creating adequate film build if you are using a high-solids, premium clearcoat. Some value-priced clears may require three coats to achieve the same degree of protection.
Knowing the film build is especially critical if the job will later be buffed. You cannot apply a film build of 2.0 mils, then buff off one-half mil. The result will leave insufficient UV absorbers or resin solids to block out the ultraviolet rays, thereby compromising durability.
Clearcoats come with certain cautions
These include:
- Dieback — The loss of gloss or matting after application can be due to many factors: too fast a solvent, improper film build, or lack of proper flash time.
- Sags — Usually occurring down a vertical surface, sags can be caused by application errors (too much at one time), or an incorrect mix ratio. Another cause is not allowing enough flash time between coats.
- Orange Peel — A clearcoat having the textured look of an orange peel can result when applying the clearcoat at too great a distance, when incorrect air pressure causes the fluid to atomize incorrectly, or if the solvent is so fast that it evaporates before the clearcoat is allowed to flow properly.
Selecting the right clearcoat for the job
Clearcoats can be divided into four major categories, primarily based on their speed of application and the jobs for which they are used: 1) air-dry express, 2) speed, 3) production, and 4) glamour. The number of panels to be repaired is a prime factor in considering which clearcoat to use; heat and humidity of the operating environment are also key considerations.
Repair size
The number of panels to be repaired should be the first consideration. If performing a spot or one-panel repair—such as a bumper cover—an air-dry express clear is a good choice. This clearcoat is especially ideal when the job needs a fast one-day turnaround. Now let us say that the repair includes a bumper cover plus one panel or three panels. Here a speed clear can be a good choice. Its three- to five-minute flash time will open up the application window wide enough to apply two coats of clear. Some collision centers prefer a general-purpose production clear to handle all types of repairs. This type of clearcoat offers adequate flash times to handle most multi-panel repairs. A glamour clearcoat is the fourth option and the right choice for large jobs or overall jobs.
Equipment
Clearcoat choices become more limited if a paint booth lacks bake capability. The longer air-dry times of production and glamour clears significantly limit paint shop throughput, so express and speed clears offer the best options. A glamour-type clear is still the best option for large or overall jobs but require an overnight dry.
The environment
Every clearcoat has a prescribed flash time, air dry, and bake standard that is generally based on an operating environment of 70°F at 50 percent humidity. Conditions exceeding these temperature and humidity levels require the use of a clear with an extended application window. It is a situation that is especially common in warm, humid conditions. For example, let us say the job is a three-panel repair and the temperature has risen to 90°F and a humidity of 70–80 percent. Normally, a speed clear would be the choice for this repair. However, in this situation, a production or glamour clear, with their longer flash times, would be the better choice.
Warranty repairs
Many OEMs are recommending approved refinish systems and procedures for warranty repairs. One procedure to pay particular attention to is the requirement to apply clearcoat from panel edge to panel edge. Blending or fading out the edge of the clearcoat is not permitted. In situations in which there is no panel break line, one might have to apply clearcoat to the quarter panel, roof, and opposite quarter to reach the final panel edge.
Paint manufacturers also have standards to meet for warranty requirements. As an example, Gareth Hughes, PPG global technical director, notes that two coats of clear applied edge to edge with a film build of 2.0 mils after buffing is required to comply with the terms of PPG’s Lifetime Limited Paint Performance Guarantee for its premium clearcoats.
Final appearance
Some factory finishes have a higher degree of texture or orange peel than others, e.g., luxury vehicles tend to have smoother, glossier finishes. So matching texture is another factor in choosing a clearcoat. In general, a glamour or slower-drying clear will flow more after being applied and provide less orange peel than a speed or express clear. Getting the surface wet enough and controlling the texture is key to achieving good appearance and texture.
There are many factors to consider when selecting and applying the right clearcoat for a repair. Pay particular attention to the product’s recommended mix ratio and flash times and the temperature and humidity of the operating environment. Equally essential is maintaining a final film build of 2.0–2.5 mils to ensure long-term durability. Of course, like any refinish product, be sure to read and follow the manufacturer’s technical and safety instructions. PPG and other major paint companies offer a choice of clearcoats to fit the job requirements. Talk to your distributor or company representative to see what options you have. Then, make the decision, keeping in mind that you will probably be using different clears for different jobs.
