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June 8 - June 14, 2015

How do you adequately assess the adhesion of a newly applied coating?

Selected Answers

From Angel Rivera of Rivera Coating Inspection & Consulting LLC on February 27, 2017:
Adhesion testing on a newly applied coating system is a no-no, but if required by the specification, a test plate can be used. If the coating system is not showing signs of premature failure, why preform a distructive test that will require repairs. Remember, you can't spell Paint without Pain !!

From Daniel Reed of Delta Engineering on August 18, 2015:
Depending on specificenvironmental conditions, such as  air and substrate temperature and humidity, an adhesion test may be conducted prior to published cure times. The interpretation of the result is key.  If it passes, GREAT, but if it fails, wait until the manufacturer's specified time and then conduct another test. If time is not critical, just wait until the specified time for testing.

From Rodney White of Independent Consultant on June 17, 2015:
Trevor and Simon are both spot-on. There should be no adhesion testing done until the coating is considered completely cured. Any testing on a "newly applied" coating would produce wildly inaccurate results. Once cured, by all means proceed with testing appropriate to the coating and the substrate.

From Simon Hope of Bilfinger Salamis on June 12, 2015:
You don't! A coating should be fully cured before any assessment of adhesion is undertaken, as you do not get a true representation of the potential performance until full cure has been achieved. I was left sorting the mess out on one occasion where a supposedly competent inspector decided that, because a newly applied internal tank coating, a phenolic epoxy, was peeling from the substrate when he pulled the masking tape up (he had been told not to touch by the contractor), the coating was defective and needed to be removed. After a full shift of blasting for two guys later, less than half a square metre had been taken off!! Still not satisfied, he demanded pull of tests done. These he did himself and proudly announced that all the tests but one had failed at below 5MPa. On analysis all the failed tests were 100% glue/coating interface failure and were because he had pulled the tests after about 8 hours when using an epoxy that took in excess of 24 hours to reach an acceptable level of cure. Also, he had failed to abrade the coating surface to provide a suitable key and remove any surface contamination! The only test that passed was the one applied on an area that had been blasted, and he had forgotten it and pulled it the following day--29MPa!! This proved pretty conclusively that the coating was fine and exceeded specified requirements, though our friend still tried to insist that he was right and that the coating should be condemned! Interestingly enough, the coating was left, and I had reports that it is still in perfect condition, having been on for some 15 years now and has been deemed fit to be put back into service for the next few years!!

From Alfredo Claussen of Instituto Mexicano del Petroleo on June 10, 2015:
Just one brief comment on the phrase: "seconds when UV curing..." Well, not so fast, my friends! Even when UV "curing" appears to be so fast, actual polymerization continues after the UV source is turned off, and adhesion/physical properties continue to change for several full hours. The process only appears to be "instantaneous," but it is not exactly finished "in seconds."

From trevor neale of TF Warren Group on June 8, 2015:
A newly applied coating needs to reach its full cure before any testing should be carried out. This may vary from seconds when UV curing is taking place on a production line to many weeks, depending on the technology, temperatures and environment. The method of evaluation will then vary with the specified DFT.

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Tagged categories: Adhesion; Asia Pacific; EMEA (Europe, Middle East and Africa); Latin America; North America; Quality control; Quality Control

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