CoatingsPro Magazine

MAY 2015

CoatingsPro offers an in-depth look at coatings based on case studies, successful business operation, new products, industry news, and the safe and profitable use of coatings and equipment.

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Page 24 of 92

24 MAY 2015 COATINGSPROMAG.COM Notes From the Blog Editor's Note: Looking for " in the feld " information about the latest coating appli- cation techniques? We invite you to join the discussion. Te following are excerpts from the NACE Corrosion Network's (NCN) and NACE Coatings Network's email-based discussion groups for corrosion profession- als, with more than 1,000 participants. Te following excerpts have been selected for their potential interest to CoatingsPro readers. Tey have been edited for clarity and length. Authors are kept anonymous for publication. Please be advised that the items are not peer-reviewed, and opinions and sug ges- tions are entirely those of the inquirers and respondents. CoatingsPro and NACE do not guarantee the accuracy of the technical solutions discussed. You' ll enjoy a variety of opinions in this practical information exchange forum. For information on how to subscribe to these free list servers, click on the "Community" link on the NACE Website: Powder Coatings vs. Liquid Applied for Architectural Structures Q: A s su m i ng t h at h i g h - qu a l - it y m ate r i a l s a re u s e d , w i l l p owde r coat i ng s p e r for m b et te r ( l a st longe r, ret a i n g los s , etc .) t h a n l iqu id - ap pl ie d coat i ng s for a rc h i - te c t u r a l st r uc t u re s , suc h a s ba lcony r a i l i ng s, u nde rc a r r i a ge s, a nd bu s she lters? A: I wou ld i m a g i ne t h at powder coat i ngs wou ld per for m bet ter i n ter m s of l i fe e x pec t a nc y ; howe ver, a s a genera l r u le, l iqu id- appl ied coat i ngs wou ld produce bet ter g loss f i n i shes. Achieving Proper Dry Film Thickness by Sanding Q: In a two-layer paint system, if the dry flm thickness (DFT) of the primer is higher than required in some areas, is it a good solution to sand these areas to the proper DFT? Does sanding afect adhesion between the two layers? A: Tis will depend on the specifed coating system. I recommend contacting the coatings manufacturer for guidelines and repair procedures. If you are the inspector, make sure you document the DFT readings on your daily reports. A: Tere's no one "fx-it" answer. Tere are as many answers as the primer and frst coat applied, depending on the coating constituents; however, your procedure should have spelled out how this should be done. Any ambiguity would have been resolved at the pre-job meeting. I insist, almost always, to convene this meeting and have issues like this resolved. For this, I suggest you have a meeting — you, the owner, the contrac- tor, and the coatings manufacturer — to guide you in the proper way forward. A: In my opinion, as long as you remove most of the dust caused by the sanding, you shouldn't lose any adhesion with most coatings. In fact, I am of the opinion that you will actually improve the inter-coat adhesion by sanding. A: Unless you are applying a primer from Company A and a coating from Company B, there should not be any problems or rejection between the two products, so if the installation of the primer is properly done, the system should be fne. A: I think everyone is pretty much on the right track here when talking in general, but without knowing exactly what the system is other than "a two-layer paint system," the safest answer would be to obtain the manufacturer's guidance. Most of the time, the high DFT areas can be sanded down, but it doesn't sound as if we are dealing with an experienced quality assurance/quality control foreman, so giving him general guidance may cause more harm than good in my opinion. A: Tere is no perfect answer to this question without knowing the coating system involved; however, one can look at several factors for guidance in this situation: 1. What does the technical department of the manufacturer say about it? Remember that they have no way of knowing what that primer looks like after its application on the site. They can only give guidance based on their general knowledge of a properly applied primer. 2. What is the condition of that primer? Is it smooth and glossy, or is it rough like sandpaper? Primers are normally low gloss, even flat finishes designed to allow the next coat of paint an opportunity to wet into the primer and gain adhesion. A gloss finish indicates a resin-rich surface, which makes it more difficult for the next coat to wet into the primer and gain adhesion. 3. How well cured is that primer? Are you still within the recommended recoat window for that primer with the particular topcoat in the system? Despite the statement "unlimited" or "extended" recoat times, there is no such thing as unlimited recoat without knowing the condition of the coating being recoated. Architectural Structures, DFT by Sanding, and Tank Priming

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