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Q. We are experiencing rust spots through the paint on an exterior steel support structure. It was painted only about 2 years ago. How do you inspect the surface? What factors might be causing the problem? A. It would appear that the paint film is not thick enough to sufficiently cover and protect the substrate. I suspect that by performing paint film thickness tests in the areas that are showing signs of corrosion, you would find the paint coverage, or Dry Film Thickness (DFT) to be insufficient. The first step to a good quality paint job is insuring that you have a good clean surface in which to build your coating system. Secondly, select a proper coating system. Use the right tool for the job. Typically the primer is applied to a DFT of 1.5 to 2.0 mils, the topcoat also is typically applied to a DFT of 1.5 to 2.0 mils giving a total DFT of between 3 to 4 dry mils. The surface may require a higher DFT if you are painting over a grit or shot blasted surface. Follow the paint manufactures recommendations to be certain you have sufficient film build to provide adequate coverage. The paint must cover the peaks or high points of the blast profile. Insufficient paint coverage over a blast profile can be the cause spot rusting. We are available to travel to your location, perform several inspection tests and confirm the application of the coating complies to the paint manufactures specifications. Please contact us for any additional information.
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© 2008 - Ron Joseph, Paint Consultant in Saratoga, California |
