Testing and performance requirements for highly pigmented primers containing zinc dust are part of new revisions to a standard from SSPC: The Society for Protective Coatings.
SSPC-Paint 29, "Zinc Dust Sacrificial Primer, Performance-Based," was updated Feb. 25.
The performance-based standard is for highly pigmented primers that contain zinc dust as the major pigment component (minimum 65 percent weight in the dry film) and are defined by their ability to protect ferrous substrates.
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SSPC revised its performance-based standard for zinc dust sacrificial primers, Paint 29, on Feb. 25.
The standard, originally issued in 1991, contains performance requirements that owners and specifiers can use for inorganic and organic zinc-pigmented primer coatings intended for spray application for use by itself or as a primer in a multi-coat system.
The new technical revisions removed the outdoor testing requirements and outdoor performance levels. Performance criteria is now based on evaluation for accelerated exposure in accordance with ASTM D5894, Standard Practice for Cyclic Salt Fog/UV Exposure of Painted Metal.
The new revisions increased the required accelerated exposure time from 3,000 hours to 5,040 hours for both inorganic and organic zinc-pigmented coatings.
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.
The maximum allowed scribe undercutting values have been increased from 0 (no undercutting) to 1/16-inch (1.6 mm) for inorganic zinc coatings and from 0 (no undercutting) to 1/8-inch (3.2 mm) for organic zinc coatings.
SSPC-Paint 29 was revised by Committee C.1.1, Zinc-Rich Coatings, which is chaired by Tony Lambrosa of The Sherwin-Williams Company.
According to SSPC, when a higher zinc loading level in the coating is desired, SSPC-Paint 20 may be specified. This specification does not cover weldable preconstruction primers, such as SSPC-Paint 30, Weld-Through Inorganic Zinc Primer.
Founded in 1950, SSPC is a nonprofit association focused on the protection and preservation of concrete, steel and other industrial and marine structures and surfaces through the use of high-performance coatings.
SSPC provides information and standards on surface preparation, coating selection, coating application, environmental regulations, and health and other issues that affect the protective coatings industry.
More information: www.sspc.org.