Automotive Painting Myths That Need To Be Cleared Up

Automotive refinishing technology has change drastically in the past 20 years. Heck, in some ways, it changes every year. New tools are invented, old tools are improved, and paint products are updated to keep up with the demands of the industry.

It’s hard to keep up with it all. Unless you work in the automotive painting industry, chances are much of the information you come across might be outdated. Recently, I did some online research to see what kind of painting information the home restoration enthusiast might come across. It was no surprise that much of it was from 20-plus years ago. One of the reasons it wasn’t a surprise, is because these are the same questions I get from customers who come into my shop.

Automotive painting

I painted this Pontiac Bonneville in 1988. The paint was lacquer. It was also the last time I painted a car with lacquer. The difference between old- and new-technology paint is like comparing old print photos to newer digital photos. The newer paints are easier to use and hold up better.

For example, several times a year, I’ll see a client who thinks we still paint with lacquer. The refinish industry made the changeover from lacquer to acrylic basecoats and urethanes back in the late 1980’s. In fact, the collision industry advanced further in the 2000’s, and developed water-based, and waterborne finishes. These are becoming the standard for collision painting because they are quicker to use and easier to blend. But for restoration and custom work, acrylic basecoats and urethanes are the way to go. And unless you’re painting a 100-point Concours restoration, there’s no need to paint with lacquer.

After doing the research and talking to other painters, I have put together a list of the top five painting myths.

You Can Mix Brands Of Paint Together. It’s All The Same.

No, it’s not. In fact, this is a myth that some professional painters even believe to be true. They will use one brand of urethane clearcoat, and then another brand of hardener or catalyst. This is a bad idea because even if the circumstances are perfect, painting can go wrong. This myth is usually created by time or budgetary constraints. Maybe the painter is using a new brand of paint, but they have product from a previous project left over and don’t want it to go to waste. Or, maybe they’ve run out of the new brand of clearcoat, and there’s still one more coat of clear that needs to be applied. If that works, then they are in the 1-percent of success rate for something like that.

It is always a bad idea to mix brands of paint on any project. When paint goes wrong, it goes very wrong. A shortcut like that can turn what was one day of work into a week – or weeks – of repair. If paint wrinkles, lifts, or stays soft, all of the damaged material must be removed.

Here are two examples of what can happen when different brands of paint are mixed together. Chemical reactions between the products can cause all kinds of problems. On the left is Crazing. On the right is lifting.

In order to take all the guesswork out of your paint project and ensure the very best results, use one brand of paint from start to finish. PPG has multiple lines of paint. I use their Deltron line. But, if I’m using the DCU 2021 urethane, I would never use the catalyst for their DC 2000 line of paint.

One big advantage to using only one line of paint is that you get to know the idiosyncrasies of that particular kind of paint, what to expect, and how it likes to be sprayed. Find what line of paint is best for the needs of your project, get all the products from that paint line, follow the instructions in the technical information sheets, and there will be no bad surprises as you’re painting.

It’s Best To Immediately Spray Any Kind Of Primer Over Bare Metal.

This myth is another one leftover from the old days of painting. Spraying the wrong product over bare metal can cause big problems like lifting and peeling. There are a variety of metal-surface treatments available. Some shops will use a metal treatment, followed by an epoxy primer, and then do the metal work. Other shops will use a metal-treatment product, then do any welding or metal work, then apply epoxy primer or go directly to bodywork and primer surfacer.

This is a hotly debated subject, but the point is to treat and protect the metal properly from the start. Don’t just grab a spray can of cheap primer and spray down the surface. Protect the surface and keep it from oxidizing.

When left unprotected, bare metal starts to flash-rust after 30 minutes at 50-percent relative humidity. A good metal treatment will protect the metal and remove the slight oxidation that happened in the hours after it was blasted. I like to use RBL Restoration Plus Wipes. PPG recommends using its SX579 Metal Cleaner followed by SX520 Metal Conditioner. Most of these products use a zinc-phosphate solution.

So next time, before the vehicle is blasted/stripped, order a metal conditioner and be ready to use it after the project comes back from blasting. But remember, each metal prep product is different. So, know the instructions for using that product.

Automotive painting

Many restoration shops use Captain Lee’s Metal Prep and Conditioner. It dries and leaves a coating of zinc oxide. Once you’re ready to do bodywork or paint, simply sand off the coating or wipe it down with lacquer thinner.

You Have To Color Sand Between Coats

It’s hard to pick which myth is the most damaging to the painted surface, but this one is the most annoying on the list. Clients will ask me if I color sand between each coat of paint. No, I do not. This is another practice from the days of lacquer materials, and no longer applies. Back then, the painter would spray black lacquer, and then, sand and buff. The result looked like glass. But if a painter was shooting candy, pearl, or metallic lacquers, they would typically apply a clearcoat lacquer over it instead of sanding and buffing the base.

One of the reasons is, if you have a pearl or metallic basecoat, sanding it will scratch it. The sandpaper cuts into the actual flakes of metallic or pearl, and there will be permanent sanding lines in the paint. Clearcoating over the scratches won’t make them go away. Sanding a candy color would create unevenness in the candy layer, as its nearly impossible to sand perfectly even.

Another factor to consider is you only want as many coats of paint on the surface as are needed for coverage. Sanding between coats of paint would compromise that coverage. Remember, unless there’s significant orange peel, roughness, or severe flaws that require repair before further basecoat and clearcoat, there’s no need to sand your basecoat.

All Hardeners For Body Filler Are The Same

Wow is that wrong! Body filler hardeners (BPO) may look the same, but they’re not! Believing this myth can lead to some serious nightmares, like body filler that never fully hardens. If this soft filler gets painted, over, there can be lifting, cracking, and all kinds of issues. The worst part is, these issues can happen months – sometimes years – after the work is done.

I talked to Carl Seaboldt of Evercoat Products, and found out why. “All manufacturers develop body-filler hardener to its own specifications. Some have a higher or lower percentage of benzoyl peroxide. [That means] what hardens its filler/putty in the stated time, might not give you the same results if used with another companies filler/putty. One of our competitor’s BPOs makes our product cure slowly, and leaves it with a tacky surface. When customers complain about dry-time issues, our first question is about the BPO. Weak or not enough BPO can lead to different types of failures. Adhesion issues, cracking, shrinking, and/or swelling can happen if the filler/putty is under-catalyzed. Over-catalyzed filler can give you staining or cracking problems.”

Some body-filler manufacturers do not clearly mark their tubes of hardener and they can look alike. Every manufacturer has its own BPO, and for the most part, they are not clearly marked. When you buy body filler it’s a good idea to mark the tube of hardener so that you know for certain which body filler it goes with.

automotive painting

Properly mixed body filler should dry hard and sand easily. The stuff that sands off should have the consistency of powder. If hardened body filler feels rubbery or sticky, then it either needs more time to dry, was mixed improperly, or maybe the wrong hardener was used.

The More Paint You Put On, The Better

This is not true. There’s a reason car manufacturer’s only use a few coats of paint. Paint – even when it’s hardened – is not as hard as metal. The more paint there is on the car, the more fragile that paint is. Think about it like this: the thicker the paint layers are, the more “give” there is to the surface.

There is no place on the vehicle where this fact is more important than on the edges of the body panels, like the edges of the doors, fenders, trunk lid, and hood. These areas are prone to chipping. In fact, some restoration shops sand those edges almost down to the bare metal after every application of primer, just to keep paint from getting thick. Paint buildup on a sharp edge is very fragile.

This 1932 Roadster was displayed at SEMA in 2004. It was painted with House of Kolor Shimrin Designer Pearl paint. The paint looks a mile deep. But, HOK’s Shimron Pearl colors are designed to look endless with minimal coats. They recommend spraying their Designer Pearl with only 2 to 3 medium coats using a 75-percent pattern overlap.

This myth doesn’t really concern filler-primer coats, as you’re going to apply as much as you need to level the surface, and much of it will be sanded off. This myth is about unnecessary base and clearcoats. Only apply as much as is needed for coverage. Different kinds of paint will require more coats than others, and some colors will cover better and need less. If I’m painting a solid color like red or black, most of the time I’ll only apply three coats. Yellow can be slightly transparent, so I first spray a coat of white, followed by three coats of yellow.

Some metallic paints don’t cover well, and with those, I’ll spray four coats. Candy, pearl, or tri-coat paints need a couple of metallic basecoat layers followed by three to four coats of candy, and then a few coats of clear to protect it all. Right there, you can easily end up with eight coats of color and clear. This means careful and even color application and attention to re-coat timing so that the solvents dry out properly is crucial.

The trick is to get your paint to look deep without it being overly thick. A correctly sprayed metallic basecoat will reflect light and have a “bottomless” look. Then the candy sprayed over it will enhance this effect. Take a look at a candy-color chart and see how deep the color looks on those paint chips. I’ve got many candy, and pearl paintjobs out there that have survived in good shape over the years, with no problems. But I am careful not to go to the extreme and apply 15 or 20 coats of color and clear.

Testing The Myths

One way to ensure success with your painting project is to create test panels. Test your paint and your process before it’s sprayed on the project. If someone insists on a certain way of painting something – test it out. Find out for certain if the method will work or if it’s just another painting myth. Always remember, the best tools in a painter’s toolbox are patience and common sense! Good luck with all your painting projects.

Article Sources

About the author

JoAnn Bortles

JoAnn Bortles is an award winning custom automotive painter, airbrush artist, certified welder/fabricator, author, and photo journalist with over 30 years of experience in the automotive industry.
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