Glass-smooth show car – or factory orange peel collision repair?
Las Vegas—It’s glass-smooth and looks miles-deep, laid over an eye-popping, sparkling custom finish on a Ridler Award-winning street rod. Or it’s a factory-like orange peel finish, designed for an invisible repair. Regardless of the desired outcome, the clearcoat is the finish everyone sees.
“It’s important to choose the right clearcoat to get the job done the way you want it and in the time you want it, but really, it’s most important to meet customer expectations,” said Jennifer Boros, director of marketing for PPG’s collision segment in the U.S. and Canada.
Boros led a group of PPG experts in the session, “Choosing a Clearcoat is not so Clear: Helping You Understand Your Choices,” which was part of the Society of Collision Repair Specialists’ OEM Collision Repair Technology Summit during its Repairer Driven Education series at the recent SEMA Show.
Understand clearcoat chemistry and the need to follow the tech sheet
Although clearcoat in the can appears simple, there is much development and testing that goes into a clearcoat before it’s brought to market to allow for ease of application, curing, and longevity, Boros said. PPG tailors multiple types of clearcoats for different applications, such as for spot repairs or overall refinishes, but “no matter what clearcoat you use, film build is key to longevity,” she said. “If you do a lot of custom work and a lot of cutting and buffing, it’s important to maintain a certain amount of film build to ensure the longevity of your finish.”
PPG Americas Technical Director Gareth Hughes noted that PPG designs its clearcoats to provide the requisite 2 mils of film build in just two coats, while some competitors’ cheaper clears may provide only 1.5 mils with two coats, which will lead to clearcoat failure as UV radiation from sunlight degrades the film down to the basecoat layer.
The UV blockers in the clearcoat are akin to a suntan lotion, but they’re designed to remain in the clearcoat film but lock into the basecoat.
“We put in enough additive so that at 2 mils, all UV light is absorbed before it can get down to the basecoat and start degrading pigments,” Hughes said. “We don’t release a clearcoat unless it withstands 5,000 hours of accelerated UV exposure, which is five years in the sun in Florida.”
Higher mil build than that can provide more protection, said Chemist Jack Dickens, but at the cost of potential application issues, such as sagging or solvent popping.
Presenters agreed that there are multiple application methods custom shops use to provide a glass-smooth finish, including applying up to five or six layers of clearcoat or applying two coats of clear, wet-sanding it, and applying two more “flow coats” of clear before a final polish. All methods are acceptable as long as 2 mils of clear film build remain in the end for protection.
Adhering to the procedures outlined in the technical data sheet is key to achieving proper product performance, including using the correct mix ratio of hardener to clearcoat. PPG chemists also spend much time selecting resins that will provide the correct hardness and durability, while allowing them to be buffed within a certain time window.
Speed selection is critical to achieving desired outcome
Painters can be tempted to select fast products to rush a job through, but they can run into problems if they use the incorrect product for the size of the job or the humidity and temperature in the spraying environment, said Application Support Specialist Darin Poston.
“If we choose too fast of a clearcoat, it wants to skim over before we have a chance to put that second coat on or to get around the area we’re spraying,” he said. “So if we have solvent entrapment, no matter what we do, it’s going to come out in the form of solvent pop.”
This problem can appear in two ways, he noted: “If I wait too long between coats, it’s going to skim and trap that solvent, or if I get on the second coat too fast, I can still trap the solvents,” which can also show in the form of [a dull appearance] dieback.
A simple test is to use a gloved finger on the masking material next to the sprayed panel; the clearcoat should feel stringy. “If I can drag my finger completely across it, I know I’ve probably waited too long. If it’s too soft, I need to give it a little bit more time.”
Match the clearcoat to the basecoat system used
“If you’re using a solvent-based system of one brand, you should use all of those products within that brand,” Boros said. “If you’re using waterborne, use all of the products within that brand, because those clears and those undercoats were developed to work with that basecoat system. Mixing and matching clearcoats over basecoats can cause pinching and dieback, as well.”
Humid conditions require same treatment as high temperatures
Clearcoats formulated for higher temperatures also work well for humid environments, Dickens said, because they stay open longer, which allow more time for the water in waterborne basecoats to dehydrate before the clearcoat cures.
“We do have a ‘torture chamber’ in our research department,” Hughes said. “We can control the temperature and humidity in a refinish spray booth that looks like it’s raining inside to make sure they do work.”