An Easy Fix for a Big Problem: Four Simple Ways to Prevent Mottling Reply

Capital City Choppers had invested heavily to promote itself during the Republic of Texas motorcycle rally in Austin, Texas.   They had shown off their best bikes and sponsored an event to get their brand in front of the tens of thousands of motorcycle enthusiasts that travel to the city each summer for one of the nation’s largest bike rallies.

Their gamble was a success:  not long after the rally ended, they began fielding calls from people who had been at the rally, seen the company’s work, and wanted to hire them for a custom chopper. In total, the company received more than enough orders to justify the expense of marketing at the event. And with new orders coming in from faraway states, this was a great opportunity for Capital City Choppers to earn some exposure in new markets.

Custom motorcycles and choppers in Austin, Texas

Motorcycles at the Republic of Texas Rally. Image Courtesy of the Austin Times

It usually took the team at Capital City Choppers three or four weeks to complete a new project.  And with business adding up, it seemed unreasonable to ask new clients to wait six months (or more) for their chopper.  To handle the influx of new business, Capital City Choppers hired a new welder, a new mechanic, and a new junior painter.

For the first couple of months things worked out just fine on the new bikes. They ran great, sounded good, and looked great….except something was wrong. The paint on the gas tanks on two recent projects didn’t sparkle the way it should. Instead, the paint was dull and splotchy.  The senior painter checked the equipment and found everything was hooked up correctly.  He made sure the paint was properly mixed and the substrate was properly cleaned.  Once these things were confirmed, the senior painter took the new hire aside and told him, “I know you are doing your best but the problem isn’t the equipment or the paint….it’s you.”

Mottling is easy to prevent...if you know why it happens in the first place.

An example of mottling due to inconsistent paint application. Image courtesy of Dupont.

If you are a professional painter, you have no doubt encountered “mottling.”  Even if you’ve never heard the proper term, you know what it looks like.  Mottling is a defect in metallic paint work that causes spots, stripes, or splotchy patches in the coating after it dries.   More specifically, mottling occurs when the metallic bits in paint are given cause and opportunity to bond together in an abnormal way.  A variety of conditions can lead to mottling.  And while tools like this BYK Mottling Meter are excellent for evaluating jobs after they have been completed, you should focus on preventing mottling as much as possible in the first place.

While we’ve spent a lot of time discussing how to prevent problems that originate in the quality or paint or tools being used, mottling is almost always the result of improper technique by the painter.  Painters that hold paint guns too close to the substrate, apply paint unevenly, or apply too thick of a wet coat to the substrate are setting themselves up for mottling to take place.

Thankfully, preventing mottling can be accomplished by simply paying attention to the process itself.  Properly mixing paint, using well-functioning air compressors and properly cleaned airbrushes, and regulating temperature in your workspace will greatly reduce instances of mottling caused by materials. From there, the burden is on you. These simple tips should reduce mottling, leaving you to be proud of a job well done instead of scratching your head, wondering why your work looks unprofessional.

  • Make sure that you are using equipment you are familiar with.  If you are using a new airbrush, first consult the technical documentation and data for the unit before starting the job.  If the documentation is not available, use the brush in a non-critical function first and evaluate the results after the paint has dried.
  • Always hold the airbrush level and parallel to your paint surface.  It’s possible that you have seen airbrush artists fling their brushes around while working. For a professional painter looking for consistent, top-quality results, you should leave the pageantry at home.  Use your tools the way they are meant to be used, which includes holding the brush level to your paint surface.
  • Apply even coats by making even passes across the substrate.  One of the best ways to not only avoid mottling but to get a smooth, even finish, is to make long, even passes with your airbrush across the paint surface.  Continue the pass until you have extended beyond the edge of the painted surface to avoid any blotches that result from releasing the brush trigger.
  • Apply multiple coats, drying and sanding for evenness between coats.  Some things can’t be rushed. Avoiding mottling and producing a gorgeous result often takes time and patience.  Applying a single, thick coat consisting of multiple passes covering each other is a leading cause of mottling.  Finding a uniform coating thickness in this manner can be near impossible and ends up wasting more time than it saves.  To get a more professional result, apply multiple coats, lightly sanding each after drying until the final topcoat is applied.

Airbrushing a Motorcycle Gas Tank. Image provided EyeKandi Art.

Thankfully, the experienced painter at Capital City Choppers was able to recognize what was happening and help his colleague learn from his mistake.  Many professional painters never stop to consider that the error could be a result of their own work; they either blame their equipment or simply paint over the mess without taking a moment to learn or absorb what has really taken place.  Mottling doesn’t have to affect your bottom line, nor cause you a headache…you simply have to be on the lookout for it and recognize the issue before it becomes a recurring problem.  Click here to learn more about proper paint thickness application!

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