Repair the bare spot, or re-galvanize?
Both standards let the galvanizer renovate small uncoated areas, but the limits are tighter than most people remember, and ASTM A123 and ISO 1461 do not draw them the same way. Enter what you found on the article and get the verdict, the limit that decides it, and the thickness the repair must reach.
The spot area is taken as length × width, which overstates an irregular spot. If the verdict is close, measure the real area.
Two standards, two different limits
Both standards allow uncoated areas to be renovated, and both cap the total at half of one percent of the surface. The single-spot rule is where they part company:
- ASTM A123/A123M-24, section 6.2.1 has no area limit for one spot. It limits shape: a spot may be longer than 25 mm (1 in.) in only one of its two dimensions. A long narrow miss along a weld can pass where a square patch of the same area fails.
- ISO 1461:2022, clause 6.3 limits each spot to 10 cm², whatever its shape.
- ASTM adds a second cap on the total (6.2.2): no more than 256 cm² per metric ton of piece weight (36 in.² per short ton). On heavy, compact pieces this cap is the one that decides, long before the 0.5% limit.
Under A123 the size limits apply only at the galvanizing facility. Once the work has left the plant, damage found later has no size cap: it is repaired to ASTM A780. Beyond the limits, or where the bare area cannot be reached for repair, A123 rejects the article, and it may be stripped and re-galvanized (6.2.4). ISO 1461 sends it back for re-galvanizing unless the purchaser and the galvanizer agree otherwise.
How thick the repair must be. Under A123 (6.2.3) zinc metallizing or zinc solder must reach the Table 1 grade for the element’s material category, and zinc-dust paint must be 75 to 100 µm (3.0–4.0 mils). ISO 1461 asks for a minimum average of 100 µm unless otherwise agreed, for example where the article will be painted over. ASTM A780 treats zinc-dust paints with 65–69% or more than 92% zinc dust in the dried film as equally effective.
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Questions
How big a bare spot can be repaired under ASTM A123?
A123-24 section 6.2.1 limits the shape, not the area: each uncoated area may exceed 25 mm (1 in.) in only one of its two dimensions. The total of all uncoated areas on the article must also stay within half of 1% of the accessible surface and within 256 cm² per metric ton of piece weight (6.2.2). Beyond either limit the article is rejected and may be stripped and re-galvanized.
How big a bare spot can be repaired under ISO 1461?
ISO 1461:2022 clause 6.3 allows renovation when the total uncoated area is at most 0.5% of the article’s surface and each single area is at most 10 cm². Larger areas mean re-galvanizing, unless the purchaser and the galvanizer agree otherwise.
How thick must the repair be?
Under ASTM A123-24 (6.2.3), zinc metallizing or zinc solder must reach the Table 1 thickness grade for the element, and paint containing zinc dust must be 75 to 100 µm (3.0 to 4.0 mils). Under ISO 1461:2022 the renovated area needs a minimum average of 100 µm unless otherwise agreed.
Damage was found on site after delivery. Do the size limits still apply?
Not under ASTM A123. Section 6.2.2 says the size limits apply only at the galvanizing facility; once the parts have left it there is no limit on the size of the area to be renovated, and the repair follows ASTM A780.