Rust Bleed / Weep Staining
Also called: brown staining at joints · acid weep
Appearance
Staining that runs from a joint onto sound coating. Fresh from the plant it is a translucent amber weep emitting from the crevice — ISO 1461 names the mechanism weld seepage, retained pre-treatment solutions escaping from narrow gaps and weld pinholes; after weathering it darkens to the familiar brown rust-stain streaking below overlaps, bolted joints and seal gaps.
Root cause
Pickling acid or pre-treatment liquor trapped in unsealed overlapping surfaces weeping out over time; NOT failure of the zinc coating itself.
Acceptance verdict
The standards take this off the coating's account explicitly. A385 names the mechanism: overlap gaps too tight for zinc to enter hold cleaning solutions instead, and those surfaces cause rust staining once the work is out in the weather — while A123 says surface conditions arising from design and fabrication deficiencies of exactly this kind are not grounds for rejecting the galvanizing. ISO 1461 goes as far as naming weld seepage from intermittent welds around overlaps an aesthetic effect that shall not be a cause for rejection. So: a design non-conformance, not a coating one — clean and monitor, and act only where the weep has genuinely attacked the surrounding coating.
This is the question the standards actually answer — describe the defect, then decide: accept, repair, or reject.
Repairable?
Not an A780 repair case. Address it at the process, not with a patch — see the remedies below.
Remedy at the plant
Flag risky overlaps at receiving inspection; do not certify sealed voids.
Remedy at design
Give every overlap one of the three honest fates. Seal-weld it completely; or leave the gap genuinely open — under about 2.4 mm zinc cannot enter, so a gap must be wide enough to wet and drain; or, where a large area is seal-welded, vent it: A385's tables require a vent hole or an unwelded length once the overlapped area reaches about 103 cm2 on steel up to 12.75 mm thick (413 cm2 on thicker steel), escalating with area. Trapped air and moisture in a sealed void develop destructive pressure at galvanizing temperature — the venting is not optional. Steel grating is the standard's own traditional exception, made without seal welding and accepted when properly executed.
Clause references
- ASTM A385/A385M-20
- ASTM A123/A123M-24
- ISO 1461:2022
- ISO 14713-2:2020
Standard designations are the property of ASTM International and ISO. This page states the acceptance outcome for this condition — it reproduces no standard text or tables. Verify against the current edition at astm.org · iso.org.