NOTE This standard covers shop-applied corrosion-protection systems for structural steel and miscellaneous metals fabricated off-site before field erection. (1.1)

NOTE Three primary system families are addressed: shop prime painting, hot-dip (batch) galvanizing, and duplex systems that combine galvanizing with a paint topcoat. (1.2)

NOTE The three families are distinguished as follows, and the choice among them is the central decision of this standard: (1.3)

NOTE This standard applies to building structural frames, open-web steel joists, miscellaneous metals (stairs, railings, lintels, embeds), ornamental ironwork, and similar steel assemblies that receive their primary corrosion protection in a fabrication shop. (1.4)

NOTE Coordination with the work of related standards. (1.5)

NOTE This standard governs only the corrosion-protection coating. The base steel, its fabrication, and its erection are governed elsewhere: (1.6)

NOTE The following are outside the scope of this standard. (1.7)

NOTE Materials, surface preparation, application, and inspection shall comply with the latest adopted edition of each of the following unless a specific edition is cited. (2.1)

NOTE The publishing body for the SSPC-SP and SSPC-PA designations is now AMPP (the Association for Materials Protection and Performance), formed by the 2021 merger of SSPC and NACE International; the legacy SSPC designations remain in active use on current project specifications and are retained here. (2.3)

NOTE Action Submittals (3.1)

NOTE Informational Submittals (3.2)

NOTE Closeout Submittals (3.3)

NOTE Applicator and galvanizer qualifications establish that the firms performing the work have demonstrated competence in the specified systems. (4.1)

NOTE Inspection governs how compliance with surface-preparation and thickness requirements is verified. (4.2)

NOTE Mock-ups and pre-application conditioning. (4.3)

NOTE The protective system is selected from the exposure category, the required service life, and the project budget. (5.1)

NOTE The default systems for typical commercial construction are SSPC-SP 6 commercial blast plus an alkyd or epoxy primer at 1.5 mils DFT for interior framing, and ASTM A123 hot-dip galvanizing for exterior miscellaneous metals (railings, lintels, embeds). The selections below depart from those defaults only where exposure or appearance demands it. (5.2)

NOTE Primer generic type determines compatibility, performance tier, and surface-preparation level. (5.3)

NOTE Inorganic zinc-rich primers (silicate binder) provide the strongest bare-steel cathodic protection and qualify many slip-critical connections, but require near-white blast preparation and accept only epoxy or urethane topcoats. Organic zinc-rich primers (epoxy binder) trade a small amount of cathodic performance for easier topcoat compatibility. Alkyd red-oxide primers are the economical choice for interior, protected steel. Epoxy and urethane primers serve intermediate barrier roles where zinc is not required. (5.4)

NOTE Alkyd topcoats shall not be applied over inorganic zinc-rich primers. (5.5)

NOTE Alkyd films saponify over the alkaline zinc-silicate surface, causing adhesion failure; only epoxy or urethane topcoats are compatible over zinc-rich primers. Because this is a boundary on what is permitted rather than an action, it is stated here as rationale; the corresponding obligation appears as a clause in the Topcoat Systems section. (5.6)

NOTE Surface preparation level is the single largest determinant of coating service life and is matched to the primer generic type. (6.1)

NOTE Standard shop prime systems require SSPC-SP 6 commercial blast cleaning, which removes all visible oil, grease, rust, and mill scale with no more than 33% staining per unit area. Inorganic zinc-rich primers and high-performance systems require the higher SSPC-SP 10 near-white blast, which limits staining to 5% per unit area. (6.2)

NOTE Shop prime painting shall be applied in accordance with SSPC-PA 1 covering surface preparation, mixing, thinning limits, application conditions, and inspection. (7.1)

NOTE Dry film thickness is specified by primer type and is the governing acceptance parameter for shop paint. (7.2)

NOTE Alkyd red-oxide primers are specified at 1.0 to 2.0 mils DFT, with 1.5 mils the typical default. Zinc-rich primers, whether inorganic or organic, are specified at 3.0 mils DFT to satisfy the SSPC Paint 20 requirement of a minimum 65% metallic zinc by weight in the dry film. (7.3)

NOTE Surfaces left uncoated in the shop must be identified so the applicator does not over-paint connection and weld areas. (7.4)

NOTE Standard practice leaves slip-critical faying surfaces, bolt holes, and a band around field welds bare; the specification must state this explicitly to avoid both bare steel where coating is required and over-painting where it is not, each of which generates RFIs. (7.5)

NOTE Shop-applied topcoats over a compatible primer extend service life and provide intermediate finish where a field finish is not the final coat. (8.1)

NOTE Hot-dip galvanizing of fabricated assemblies shall conform to ASTM A123, and hardware items shall conform to ASTM A153. (9.1)

NOTE ASTM A123 governs batch galvanizing of fabricated structural shapes, plates, and bars; ASTM A153 governs fasteners and miscellaneous hardware that are centrifuged (spun) after dipping. The two standards have different thickness tables and different handling, and citing A123 for hardware (or substituting continuously galvanized A653 sheet for batch-galvanized fabrications) is a common and consequential error. (9.2)

NOTE Minimum average coating thickness is set by the ASTM A123 material category, which depends on steel thickness. (9.3)

NOTE Per ASTM A123/A123M-24 Table 1, structural shapes and plates 3/16 in. and thicker require a minimum average coating of 85 µm (3.4 mils); material from 1/8 in. to less than 3/16 in. requires 65 µm; material thinner than 1/8 in. requires 45 µm. ASTM A153 Class C fasteners 3/8 in. diameter and larger require a minimum average of 43 µm (1.7 mils), and Class D fasteners smaller than 3/8 in. require 25 µm (1.0 mil). (9.4)

NOTE Galvanized nuts shall be over-tapped after galvanizing in accordance with ASME B18.2.2 or ASTM A563 to accommodate the coating on the bolt threads. (9.5)

NOTE Over-tapping is required because the zinc coating thickens the bolt threads; nuts tapped to standard dimensions before galvanizing will not run onto a galvanized bolt. This obligation is stated as a clause below. (9.6)

NOTE Design for galvanizing must provide for venting, drainage, and steel chemistry control per ASTM A385. (9.7)

NOTE Welded assemblies with trapped air or sealed hollow sections can blow out explosively during immersion in the molten bath; ASTM A385 requires that all surfaces be welded and that vent and drain holes be provided. Steel chemistry also governs coating quality: silicon in the Sandelin range (roughly 0.04% to 0.15%) produces thick, dull-gray, brittle coatings, so reactive-steel control is required where appearance or bend-after-galvanize behavior matters. (9.8)

NOTE A duplex system applies a paint or powder topcoat over hot-dip galvanizing where color, appearance, or aggressive exposure demands more than galvanizing alone. (10.1)

NOTE The duplex system service life is synergistic: industry data places it at 1.5 to 2.3 times the sum of the individual galvanizing and paint service lives. Realizing that synergy depends entirely on correct surface preparation of the galvanized surface before topcoating. (10.2)

NOTE Galvanized surfaces shall be prepared in accordance with ASTM D6386 before painting, or ASTM D7803 before powder coating. (10.3)

NOTE Painting directly over fresh galvanizing -- particularly over wet-storage stain (white rust) -- causes rapid delamination. ASTM D6386 requires sweep blasting, weathering, or chemical passivation to provide a sound surface for the topcoat; omitting this preparation is the most common cause of duplex-system failure. (10.4)

NOTE Faying surfaces of slip-critical (friction-type) bolted connections require a defined surface condition so the connection develops its design slip resistance. (11.1)

NOTE The slip resistance of a connection depends on the faying-surface coating. AISC 303 defines Class B faying surfaces with a mean slip coefficient of not less than 0.50. Inorganic zinc-rich primers at 3 mils DFT typically qualify as Class B, but only the specific product's certified test report establishes that; not all zinc-rich primers qualify. Galvanized faying surfaces are not Class B as deposited and must be conditioned. (11.2)

NOTE Damaged galvanizing, cut edges, copes, and field welds shall be repaired in accordance with ASTM A780. (12.1)

NOTE Repair of bare areas is frequently omitted from specifications, leaving cut edges and field-weld zones unprotected after erection. ASTM A780 defines acceptable methods -- zinc-rich paint, zinc solder (zinc-based alloy), or thermal-spray zinc -- and the repaired film thickness must at least match the parent coating. (12.2)

NOTE The sequence of welding, galvanizing, and painting must be coordinated and shown on the structural drawings before shop drawings are issued. (13.1)

NOTE Galvanize-after-weld is strongly preferred over weld-after-galvanize because welding through a galvanized coating burns off the zinc and generates fume; the structural engineer must flag members to be galvanized so that hole sizing, vent requirements, and camber can be addressed before fabrication. Where galvanizing and shop prime are both specified on a single assembly, the precedence and the boundaries must be explicit, or the fabricator cannot proceed without an RFI. (13.2)

NOTE The specific members to be galvanized, and the locations of vent and drain holes on enclosed sections, are shown on the structural drawings. galvanized member schedule (13.2.5)

NOTE Coated and galvanized steel shall be handled and stored to prevent coating damage and wet-storage staining. (14.1)

NOTE The Contractor shall warrant the shop-applied coating systems against defective materials and workmanship for the specified period. (15.1)