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October 2 - October 6, 2017

What is the best way to remedy over-thickness of a topcoat after it has dried and cured?

Selected Answers

From Greg Thorpe of Hertel Modern on October 10, 2017:
Depending on the extent of the "highs," we've found that using abrasive sand paper (120 grit or finer) usually works well. Keep a DFT gauge on site to ensure the desired DFT is reached. Clean the area of dust and residue before spraying a cover coat to hide the sanding marks. Be sure to soft-edge the masking around the repair site to help blend in the repair to the rest of the top coat. We've used this approach extensively on the LNG plant here in Australia and always had good results.

From David Grove of The Grove Real Estate Group on October 6, 2017:
All answers appear to be good; however, I believe that Mr. David Hopkins provided the best response because the type of coating was not identified nor the reason for requiring removal. Imagine if the topcoat provided a seal to a softer waterborne, intumescent fireproofing and thickness impacted the UL requirements. As Mr. Erik Andreassen identified, the coatings manufacturer should be involved with the decision. Good job to you all!

From Warren Brand of Chicago Corrosion Group on October 5, 2017:
The question implies that it has already been determined that the topcoat is too thick and needs to be reduced. If the surface is a hard surface, such as an epoxy or urethane, you could try abrasive blasting with a very fine aggregate. However, this will remove any gloss and will be difficult to control. Further, great care must be taken to ensure that the blasting does not fracture the coating system and/or degrade its adhesion the the substrate or primers. If this is in a tank interior, this may not be an issue, particularly if you're working with a thick coating system, say above 25 mils, and need to remove only 3-5 mils. On anything exterior it becomes far more difficult due to aesthetics. In terms of costs, it may be easier to remove the topcoat completely down to either the primer or steel and recoat.

From Elvis Sequeira of Berger Paints Emirates Ltd on October 5, 2017:
I agree with the first two responses. In addition, after total cure of the applied paint system, in consultation with contractor and client, a pull-off adhesion test could be done to determine the pull-off strength, and then the final decision will be taken by the manufacturer to OK or give a suitable recommendation.

From Erik Andreassen of CPS on October 3, 2017:
Check with the coating supplier's data and technical service before making a decision. Refer to the DFT requirements in the specification. If the answer is exceeding all requirements, request the coating supplier to recommend a correct approved repair procedure for his material and get approval from your client to continue. Document all correspondence for future issues and Q.C. reports.

From david hopkins of Retired on October 3, 2017:
What type of topcoat--is it for chemical or UV protection? Is it a gloss finish; is it epoxy or urethane or water-based or enamel? Unless all details are supplied, no qualified answer can be given.

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Tagged categories: Coating/Film Thickness; Paint application; Quality control; Quality Control; Topcoats

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