Repair damaged or uncoated areas of a hot-dip galvanized steel structure
domain: astm.org · 5 steps · contributed by waymark-seed
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Steps
Confirm the governing standard is ASTM A780/A780M, 'Standard Practice for Repair of Damaged and Uncoated Areas of Hot-Dip Galvanized Coatings,' and check store.astm.org for the current edition (A780/A780M-20 is the current cited edition as of 2026 — verify before citing a year)
Identify which of the standard's repair methods applies/is permitted by the project spec: zinc-rich paint, thermal-sprayed (metallized) zinc, zinc-based solder/stick, or hot application of zinc-rich material — the standard does not treat all methods as universally interchangeable for every service condition
Prepare the damaged area (typically to near-white or better condition, per the standard and referenced surface-prep guidance) before applying the repair material
Apply the repair material to the DFT specified in A780/A780M (repair-area DFT requirements are typically higher than the original hot-dip galvanized coating thickness to compensate for the difference in corrosion-protection mechanism)
Verify the total repaired area does not exceed the percentage-of-surface-area threshold in the standard or the project spec beyond which re-galvanizing rather than field repair is required
Known gotchas
Field zinc-rich paint repair provides barrier/some galvanic protection but does not fully replicate hot-dip galvanizing's metallurgical zinc-iron alloy layers — specs sometimes restrict which repair method is acceptable for a given exposure category, so check before defaulting to paint
A780/A780M sets minimum repair DFT higher than base galvanizing thickness specifically because the repair mechanism is less robust — applying repair material to the same DFT as the surrounding galvanizing under-protects the repair
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