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January 14 - January 18, 2019

What do you do when the surface profile is higher than the dry film thickness of the specified primer?

Selected Answers

From Larry Muzia of Exceletech Coating & Applications, LLC on January 21, 2019:
Reducing the depth of profile is one solution but usually not the best way to deal with the issue. I would go back to the specifier and coating supplier to get a recommendation of utilizing a primer that is formulated to achieve the necessary film thickness to not only coat the valleys but also to cover at least 2 mils over the peaks. Inorganic zincs are prone to mudcracking/splitting when applied too heavily and organic films may be subject to solvent entrapment or excessive film stress; however, in most cases, excessive profile depth can be handled with a switch to a primer suitable for the depth.

From Warren Brand of Chicago Corrosion Group on January 16, 2019:
This is a complicated question, which Jeff, David and Jon have addressed nicely. The bigger issue is what will the DFT of the entire system be? If you're applying a thick system, say, >30 mils, then the blast profile may not be deep enough to provide sufficient adhesion for long-term performance. We need to look at what caused the issue in the first place. If the primer was applied too thin, then the aforementioned comments are spot on. If the blast was too shallow, that opens up a completely different can of worms.

From Jon Cavallo of Sponge-Jet Inc. on January 15, 2019:
Simple solution - Re-blast the affected substrate area with a finer abrasive to obtain the correct profile. Applying an excessively thick primer usually results in disaster (solvent entrapment, blistering, etc.).

From David Grove of The Grove Real Estate Group on January 14, 2019:
The solutions have only been touched upon as presented. You can not add an additional primer if there could be solvent entrapment, or if during the minimum drying time for recoating, there was surface corrosion development on the peaks of the profile and the primer is not an inhibitor type. As a result, several things have to be evaluated: the actual surface condition (looking for corrosion and/or contamination) after the minimum recoat time has been reached; ensuring that the applied coating can accept an additional recoat that meets the specifications and/or is tolerant to the surface condition. It is important to remember that coating systems may have a maximum thickness for the environment or location, and individual coatings may have a min-max limitation that will not meet the system’s requirements for the actual location. With a question that does not provide specifics, the course I would choose is, to discuss this in advance with the responsible parties (owner’s rep., manufacturer, and the applicator) before- hand and agree on specific factors forward and ensure documentation of the agreement is recorded as well as the details of any occurrences on site. With my specifications, I always ensured that the applicators could actually see when they had sufficient coverage by the coatings’ wet appearance during application, etc. We were very successful, and of course, I had excellent support from my team to achieve these results. Have a safe and great 2019!

From Jeff Kim of Sherwin-Williams on January 14, 2019:
For organic primers, one solution is to apply an additional coat of primer to comply with specified DFT. If the primer is an inorganic zinc, additional coats are generally not advised unless the manufacturer's instructions specifically permit this practice. Primer should cover profile peaks by at least 2 mils DFT to prevent pinpoint rusting..

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Tagged categories: Dry Film Thickness (DFT); Quality Control; Quality control; Surface profile

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