CoatingsPro Magazine

JUL 2016

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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56 JULY 2016 COATINGSPROMAG.COM cause any signifcant issue other than a minor cosmetic one; however, repairs to the afected area could create more signifcant cosmetic issues. W hen pinholes are present in an applied coating flm, they can be very difcult to repair, and they cannot typically be corrected by applying additional coatings alone. Te surface tension of the coatings material tends to further magnify the defect and will not bridge over the void. Removal of the coating layers exhibiting pinholes is typically required, although sometimes brushing and rolling the coatings into the voids has limited success. Defects that fall into the pinhole categor y can also be confused w ith cratering and fish-eyes. T hey all have a similar visual appearance. Fish-eyes are ty pically caused by a contaminant on the surface, such as an oil, that resists the coating film and results in a circular crater that extends to the surface that was contaminated. T hat surface could be the substrate or an underly ing application of paint. Craters ty pically tend to be larger and more shallow ty pes of voids in the coating film. In this case, the evidence showed that the voids were in fact pinholes, and we recommended that the contrac- tor adjust the application process to minimize the formation of pinholes. Tis was accomplished by allowing the inorganic zinc primer to properly cure before additional coats were applied and to apply a mist coat of the interme- diate epoxy to plug the porosity of the inorganic zinc primer. Moving Forward Pinholes can be a problem. Terefore, the best practice is to try to avoid creat- ing pinholes during application in the frst place. Tey are typically created by poor application techniques, including: • Excessive atomization pressure • Dry spray • Air trapped in a porous previous coat (inorganic zinc and concrete) • Poor spray technique With inorganic zinc, it's imperative to allow the material to cure properly before applying the intermediate coat. Other signifcant issues can manifest from applying additional coatings material to uncured inorganic zinc. A Photo 2. This is a coating that typically would require replacement due to the poorly formed coating film. When pinholes are present in an applied coating flm, they can be very difcult to repair, and they cannot typically be corrected by applying additional coatings alone. Illustration 2. Pinholes developing in intermediate and topcoat from outgassing of the inorganic zinc primer during the application of the intermediate coat. Pinholes

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