CoatingsPro Magazine

JUL 2018

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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COATINGSPRO JULY 2018 55 evident as compared to the typical red-oxide-primed surface. e customer had chosen the white primer to provide a bright and well-lighted work area for the manufacturing facility. Substantial discoloration of the white painted surfaces was apparent during the preliminary walkthrough. A lthough corrosion was observed, the majority of the "defect" was staining from the corrosion/rusting activity. e white surfaces provided a perfect background to contrast and highlight the corrosion and related staining. A ll of the fabricated columns, roof beams, and roof joists had received the white shop-applied alkyd primer. Diagonal rod bracing and other appurtenances to the structural steel were coated with the same material as well. e girts (horizontal bracing components) and roof deck panels with the ceiling side visible had both been factory coil-coated with a thin-film (<1 mil, or 25.4 microns) acrylic coating materials with a baked curing cycle. e various structural elements of the building and their respective coating materials can be grouped into the following categories: White shop-applied primer w Columns and roof beams w Roof joists Factory-applied thin-film acrylic coil-coatings applied by the manufacturer w Girts w Roof panels (visible ceiling side that was exhibiting corrosion and staining) e general condition of the build- ing interior was not what would have been expected of a newly constructed facility. e question of coatings failure and/or non-conformance to the specification was a difficult one. e specification as written was not detailed as to coating material and its instal- lation requirements, and it depended more upon the typical manufacturing process norms. ere were clearly many assumptions made about how to inter- pret the specification. Some Background Typically, the primers used for metal building structures are classified as SSPC Paint Specification No. 15 coatings. According to the Metal Systems Building Manual, MBMA (Metal Building Manufacturer's Association)—4.2.4 Structural Framing Shop Primer, "It is common industry practice for metal building manufacturers to use the SSPC Paint Specification No. 15 for the primer used on primary and secondary struc- tural members. A description of the coating material from the SSPC: Paint Specification 15 is as follows: 1.1 is specification covers a one coat shop-ap- plied primer for open web and long span steel joist and joist girders and for cold formed steel framing, and primary and secondary structural framing for metal buildings. is coating is intended to provide temporary protection to the steel joist during delivery, storage on site, and erection in an atmosphere comparable with SSPC Environmental Zone 1, normally dry. is coating is intended to be used as a holding primer that may or may not be removed before or after erection or assembly in the field." e material, as described above, is intended for service environments, such as SSPC Environmental Zone 1. From Using SSPC Coating Material Standards, a Zone 1 normally dry is further defined as: • 1A–Interior, normally dry (or temporary protection). Very mild. • 1B–Exterior, normally dry. Coatings may be subject to exposure to sunlight. Zone 1A-Interior would be the service environment expected within the interior of a building when complete. However, during construc- tion, those ultimately interior bound materials are unfortunately stored in a laydown yard outside and exposed to the elements. It's reasonable to assume that the coated materials were exposed to rain, the resulting ponding water, and weathering while in the laydown yard, and, because of that exposure, began to corrode and stain the white coated surfaces. With longer exposure to the elements, more corrosion of the surfaces would be expected. is would have explained why some areas erected earlier exhibited lower levels of corrosion and coatings defects. e primer applied to the structural steel was acceptable as specified, but it was not intended to provide any extended protection in an exterior environment for long durations. e primer applied to the columns and joists corroded as would be expected with extended exposure to the elements. Regarding the acrylic coil-coated building materials, ceiling panels, and girts, the rust staining was typically caused by the cutting of the materials to achieve a specific length. e ends Corrosion and staining evident on the structural steel Staining on Structural Steel

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