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October 9 - October 13, 2017

Should pull-off adhesion tests be carried out on a zinc-rich primer alone, or only on a complete system?

Selected Answers

From Patrick Jansen of IFO-Nederland on November 20, 2017:
I prefer on a complete system (if I see the surface preparation with anchor profile). If you will test this at the end, you have a complete test overview. Otherwise, you make a destructive test on an incomplete system. And according the specifications, you must wait till the primer coat has been cured, causing more delay. If I don't see any preparation, then it is may be better to do the test on the primer to know the basics are good enough to build a system on.

From David Grove of The Grove Real Estate Group on October 23, 2017:
I propose that a simple question be asked. What is the purpose of the tests because most IOZ's cannot be touched up easily or at all without re-prepping? If the surface prep and conditions were acceptable, then I would try to delay any pull-off testing until the system is completed. If you wait until the IOZ is fully cured, further delays may mean that contamination can become an issue. The site conditions should be the determining factor in what occurs. For all IOZ coating systems, I suggest that the full application process be followed by inspection.

From Marco Fabio Ramenzoni of ZINGA METALL BRASIL on October 13, 2017:
The purpose of a TRUE ZINC RICH coating application, both as a primer and as a single system, is to protect actively the steel substrate. It must be tightly adhered to the recommended treated steel surface, so to perform freely its electrochemical conduction and, therefore, its full cathodic protection. In any case, the adhesion should always be measured on the full system applied and cured. After all, it is the designed and recommended systems that must perform and not only just a part of it. Some extremely zinc rich coatings may have growing results on adhesion testing with time, starting from 4.1 MPa and going up to as much as well above 7 MPa, or more, within a few weeks or even months from the initial application. Perhaps, as a suggestion, the adhesion testing measurements should be taken both after  7-days  and 6 months of exposure, always for the full system, exposed to either accelerated or regular environments.

From amar jit singh of NIC T Pune on October 11, 2017:
The test to evaluate adhesion has changed from ASTM D3359 (cross-cut) to ASTM D4541 (pull-off). Revised Paint 29 requires adhesion testing to be performed on the cured primer prior to and following accelerated exposure with a minimum adhesion requirement of 600 psi (4.1 MPa) for each of four pulls on unscribed areas of three test panels.

From Ajay Sunke of ASSETReifurb Engineerr on October 9, 2017:
The objective of using a zinc-rich primer is to protect the surface as a sacrificial anode and form a protective film once the topcoat gets damaged. Looking at the objective of the primer, it is always topcoated with a compatible coating. And hence, the adhesion between the top coat and zinc-rich primer is more important then the adhesion of zinc-rich primer to the metal surface. After an  adhesion failure of the topcoat, the zinc embedded in the primer will come into the picture and start working its role of sacrificial anode and form a well adhered film. Hence, the important is to measure the intercoat adhesion between topcoat and zinc-rich primer as a complete system and not of the zinc-rich primer alone.

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Tagged categories: Adhesion; Primers; Quality control; Quality Control; Site/field testing; Zinc-rich (inorganic); Zinc-rich (organic)

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