SSPC-SP 16 Brush-Off Blast Cleaning of Coated and Uncoated Galvanized Steel, Stainless Steels, and Non-Ferrous Metals
Nonmandatory Appendix A: Explanatory Notes
Brush-Off Blast Cleaning Galvanized Steel
A9.1 Thickness of Zinc on Galvanized Steel: The zinc layers should remain intact during brush-off blast cleaning. The rate of cleaning is typically 110 m2 per hour (1200 ft2 per hour) or greater. It is recommended that the thickness of new galvanizing be measured before and after brush-off blast cleaning using measurement techniques described in SSPC-PA 2 to confirm that it still conforms to ASTM A123 or ASTM A153A/153M, as applicable. Any areas with insufficient thickness should be repaired in accordance with ASTM A 780.20,21,22
A9.1.1 For some complicated shapes, a reduction in galvanizing thickness may be difficult to avoid. A mock-up or test area should be abrasive blasted to determine if excessive zinc is removed. If this is the case, consideration should be given to replacing the zinc (e.g. spot applications of an organic zinc-rich primer) or alternative measures of surface preparation such as zinc phosphate treatment may be used. These methods are beyond the scope of this standard.
A9.2 Zinc Oxides: Newly exposed zinc surfaces will oxidize rapidly, especially in the presence of moisture. During brush-off blast cleaning and subsequent painting of galvanized steel, the surface temperature should be a minimum of 3 °C (5 °F) above the dew point, in order to retard the formation of zinc oxides. To limit the amount of zinc oxide on the cleaned surface, galvanizing should not be permitted to get damp after cleaning, and should be painted as soon as possible within the same work shift that the surfaces were cleaned.
A9.3 On galvanized steel surfaces, the use of wet abrasive blast cleaning can result in formation of oxides and hydroxides. Additional information on the preparation of galvanized steel for painting can be found in ASTM D 6386.23
SSPC-SP 16 Brush-Off Blast Cleaning of Coated and Uncoated Galvanized Steel, Stainless Steels, and Non-Ferrous Metals, SSPC: The Society for Protective Coatings, Pittsburgh, PA, 2010, www.sspc.org
ASTM D6386 Standard Practice for Preparation of Zinc (Hot-Dip Galvanized) Coated Iron and Steel Product and Hardware Surfaces for Painting
Significance and Use
This practice describes the procedures that can be used to prepare new and weathered zinc-coated surfaces on after-fabrication steel products for painting, and that can improve the bond of paint to the zinc surface.
Scope
This practice describes methods of preparing surfaces of new and weathered hot-dip galvanized steel for painting with liquid paint and coating products. Preparing surfaces of new and partially weathered galvanized steel for powder coating is addressed in Practice D7803. Hot-dip galvanized steel is produced by the immersion of fabricated or unfabricated products in a bath of molten zinc, as specified in Specifications A123/A123M or A153/A153M. This practice covers surface preparation on iron and steel products and hardware that have not been painted previously. Galvanized surfaces may have been treated with protective coatings to prevent the occurrence of wet storage stain. This practice does not apply to sheet galvanized steel products nor to the coil coating or continuous roller coating processes. Sheet and coil surface preparation can be done in accordance with Practice D7396.
ASTM D6386-16a, Standard Practice for Preparation of Zinc (Hot-Dip Galvanized) Coated Iron and Steel Product and Hardware Surfaces for Painting, ASTM International, West Conshohocken, PA, 2016, www.astm.org
http://www.astm.org/cgi-bin/resolver.cgi?D6386
ASTM D7396 Standard Guide for Preparation of New, Continuous Zinc-Coated (Galvanized) Steel Surfaces for Painting
Significance and Use
This guide describes procedures that can be used to prepare new zinc-coated surfaces for painting and improve the bond of paint to the zinc surface.
Scope
This guide covers surface cleaning and various methods for treating new, continuous zinc-coated (galvanized) steel surfaces produced by either the hot-dip method or by electroplating. This guide is applicable to only surface preparation for application of liquid paint and coating products, and not for powder coating applications. This guide covers surfaces that have not been treated previously at the mill to provide temporary protection against staining by moisture other than by easily removed protective oils (see Appendix X1). For preparing surfaces of new or weathered items of zinc-coated steel produced by batch processing, refer to Practice D6386.
ASTM D7396-14, Standard Guide for Preparation of New, Continuous Zinc-Coated (Galvanized) Steel Surfaces for Painting, ASTM International, West Conshohocken, PA, 2014, www.astm.org
http://www.astm.org/cgi-bin/resolver.cgi?D7396
The American Galvanizers Association (AGA)
Publications
Duplex Systems Generate Excellent Return on Investment
Preparing Hot-Dip Galvanized Steel For Powder Coating DVD
Preparing HDG Steel for Paint (CD Version)
Preparing HDG Steel for Paint (DVD Version)
HDG vs. Paint in Life-Cycle Assessment Case Study 2: Parking Structures
HDG vs. Paint in Life-Cycle Assessment Case Study 1: Balcony Structures
Hot-Dip Galvanized Steel vs. Zinc-Rich Paint
Suggested Specification for Preparing Hot-Dip Galvanized Steel Surfaces for Painting
A Victory Over Paint for Galvanizing
Duplex Systems: Painting Over Hot-Dip Galvanized Steel
Hot-Dip Galvanized Steel vs. Paint
https://galvanizeit.org/education-and-resources/publications
Search Title:
Preparing and Painting Galvanizing
Hot Dip Galvanizing Versus Zinc Rich Primers