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Hot-Dip Galvanizing Defect & Appearance Photos

Everyone can describe a galvanizing defect. The question that actually decides the job is different: do you accept it, repair it, or reject it? Every entry here answers that against ASTM A123 and ISO 1461 — from real plant photos, not renders.

Verdict:
Close-up of a galvanized beam surface scattered with small raised dross pimples in the zinc coating
Hard, gritty particles felt and seen in or under the coating; surface looks peppered or sandy, sometimes with raised pimples.
REJECT IF GROSS

Dross Inclusions

Also called: dross pimples · gritty coating

Why it happens. Zinc-iron intermetallic particles (FeZn13) from the kettle bottom stirred into the working zinc — dragging work too deep, excessive dross generation from reactive steel, or overdue dross removal.

ASTM A123/A123M-24ISO 1461:2022

Full guide — causes, remedies and clause references
Galvanized beam photographed from below: a broad chalky grey-white ash deposit spreads across the web with soft feathered edges, clearly lighter than the sound zinc beside it, and the same deposit continues as a dark band under the top flange where it falls into shadow
Dull grey-white deposits or streaks on the surface; loosely adherent ash sitting on or lightly bonded into the top of the coating.
ACCEPT AFTER CLEANING

Ash Inclusions

Also called: skimming marks · ash staining

Why it happens. Zinc oxide/ash film on the bath surface pulled onto the work during withdrawal — inadequate skimming ahead of the withdrawal path or too-slow withdrawal.

ISO 1461:2022ASTM A123/A123M-24

Full guide — causes, remedies and clause references
Galvanized steel tubes stacked on a rack: elongated black bare patches run along the upper face of the nearest tube where the zinc never took, with sound bright coating surrounding each patch
Exposed steel with no zinc — from pinhead spots to patches; edges of the surrounding coating are usually sound.
REPAIRABLE

Bare Spots (Uncoated Areas)

Also called: misses · black spots

Why it happens. Two different failures produce the same bare steel, and they belong to different people.

ASTM A123/A123M-24ASTM A780/A780M-20ISO 1461:2022

Full guide — causes, remedies and clause references
Galvanized channel section with white powdery wet-storage stain deposits spread across the face around drilled holes
White to grey powdery deposit, from light film to bulky build-up, typically where surfaces were stacked in contact.
ACCEPT AFTER CLEANING

Wet-Storage Stain (White Rust)

Also called: white rust · storage stain

Why it happens. Moisture trapped between closely packed, freshly galvanized surfaces without air circulation — zinc corrodes rapidly before its protective patina forms.

ISO 1461:2022ISO 14713-2:2020GA UK wet storage stain guidance

Full guide — causes, remedies and clause references
Close-up of a galvanized fillet weld corner: a broad translucent yellow-ochre flux film lies across the flange face with fine white crystalline speckles through it, while the weld bead itself is fully galvanized with its ripples clearly visible under sound zinc
Two modes, and they are not equally serious. INCLUSION: black/brown rough patches or crusty residue bonded into the coating, sometimes with bare steel underneath when picked off — flux stopped the zinc wetting the steel. STAINING: a broad translucent yellow-ochre film lying on top of otherwise sound coating, often with fine white crystalline speckles through it and the zinc's spangle still legible through the film, because nothing has been displaced. Look at the weld bead to tell flux from welding slag: with flux the bead is galvanized and the residue sits on top of sound zinc, whereas welding slag leaves a bare crusty ridge tracing the weld toe with no zinc on it at all.
REPAIRABLE

Flux Inclusions & Flux Staining

Also called: flux burn · black flux spots

Why it happens. Flux carried on the work into the zinc (poor drying, flux too dense) or floating flux/skimmings contacting the work in wet-galvanizing practice; inadequate skimming.

ISO 1461:2022ASTM A123/A123M-24ASTM A780/A780M-20

Full guide — causes, remedies and clause references
Galvanized gusset and base-plate connection: a brown crusty slag ridge runs along the weld toes with no zinc on it, rust stain bleeds onto the coating below, and round weld spatter nodules are scattered across the gusset face
A hard crusty ridge tracing the weld toe with no zinc on it, rusting brown and bleeding stain onto the sound coating either side; hard spherical nodules scattered around the weld, either coated over as roughness or shed to leave uncoated points.
REPAIRABLE

Uncleaned Welding Slag & Spatter

Also called: slag line · weld spatter · uncleaned welds

Why it happens. Welding slag and spatter left on the steel before it reached the galvanizer.

ASTM A385/A385MASTM A123/A123M-24ASTM A780/A780M-20ISO 1461:2022ISO 14713-2:2020

Full guide — causes, remedies and clause references
Two galvanized steel sections photographed after being separated: each carries a dull grey contact patch with straight edges where the pieces were stuck together in the zinc bath, against otherwise bright coating
Dull grey patches with straight, geometric edges that match the footprint of another piece — and the same mark appears on both mating faces. After the pieces are pulled apart the zinc in the patch may be torn, scored or missing, sometimes with a raised lip or drag mark at its edge. The straight edge is the tell: a contact mark has a geometry, because it is the shadow of another piece of steel. Reactive-steel grey has a chemistry instead — it is cloudy, follows the section, and is usually thicker rather than thinner.
REPAIRABLE

Articles Stuck Together / Contact Marks

Also called: contact marks · touch marks · stuck bundles

Why it happens. Articles touching one another during immersion, in the bath, or on withdrawal — too little spacing on the jig, nested or bundled sections, pieces resting on each other.

ASTM A123/A123M-24ASTM A780/A780M-20ISO 1461:2022ISO 14713-2:2020

Full guide — causes, remedies and clause references
Internal corner of a galvanized steel fabrication: a thick lumpy mass of solidified zinc has pooled on the horizontal gusset plate, which has no drain hole, while the surrounding faces carry bright normal coating
Thick pooling of solidified zinc that could not drain, accumulated in corners, on gussets and inside sections; drips and runs along lower edges; spikes and icicles hanging at drain points.
ACCEPT

Lumps, Runs & Drainage Spikes

Also called: zinc icicles · drips · puddling

Why it happens. Zinc that could not drain before solidifying — withdrawal too fast, poor drainage orientation on the jig, or drain holes that are undersized, mis-placed, or simply absent.

ASTM A123/A123M-24ISO 1461:2022ISO 14713-2:2020

Full guide — causes, remedies and clause references
Large galvanized pipe bend with a flange: the elbow shows a dull matte grey coating while the adjoining straight pipe shows bright spangle, in the same assembly
Uniform or patchy dark grey, matte surface — no bright spangle; sometimes a cellular or net-like pattern; often thicker than normal.
ACCEPT

Matte Grey / Dull Coating

Also called: grey coating · mottled coating · reactive steel finish

Why it happens. Reactive steel chemistry (Sandelin-range or high silicon) driving zinc-iron alloy layers to grow through the free zinc layer; slow cooling of heavy sections has the same effect.

ASTM A123/A123M-24ISO 1461:2022ISO 14713-2:2020

Full guide — causes, remedies and clause references
Wide galvanized panel with scattered raised blisters erupting through the coating, their pale broken crowns standing out against the smooth darker zinc surface
Small raised bumps or blisters in the coating, intact when probed or occasionally hollow.
REJECT

Blisters & Pimples

Also called: hydrogen blisters

Why it happens. Hydrogen absorbed during pickling erupting at galvanizing temperature (worst on hard/high-strength steel), or steel surface defects and subsurface inclusions opening at 450 C.

ASTM A143/A143M-22ISO 1461:2022

Full guide — causes, remedies and clause references
Galvanized bar welded into a base plate: translucent amber liquor weeps from the joint crevice and spreads over the surrounding sound coating, with darker crusted residue at the gap itself
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.
NOT A COATING DEFECT

Rust Bleed / Weep Staining

Also called: brown staining at joints · acid weep

Why it happens. Pickling acid or pre-treatment liquor trapped in unsealed overlapping surfaces weeping out over time; NOT failure of the zinc coating itself.

ASTM A385/A385M-20ASTM A123/A123M-24ISO 1461:2022ISO 14713-2:2020

Full guide — causes, remedies and clause references
Galvanized tubular section photographed close up: a coarse granular coating texture shows along the band of raking light, with no isolated lumps or inclusions
Uniformly coarse, textured coating over large areas rather than isolated particles.
ACCEPT

General Roughness

Also called: rough coating · orange peel

Why it happens. Over-pickled or coarse steel surface, reactive chemistry, high bath temperature, or excessive coating thickness on slow-drained work.

ASTM A123/A123M-24ISO 1461:2022

Full guide — causes, remedies and clause references
Thin galvanized steel plates hanging on wires after the kettle, buckled into deep S-curves and waves along their length while the zinc coating on them stays bright and sound
Members bowed, twisted, or panels oil-canned after galvanizing — plus a third mode that catches people out: the assembly stays straight but a joint lets go. Where a thin plate is intermittently welded to a heavy section, the unwelded lengths between the welds lift away from it and leave an open slot along the interface. In every case the coating itself is sound — what moved is the steel.
NOT A COATING DEFECT

Distortion & Warpage

Also called: warping · twist after galvanizing

Why it happens. Relief of residual fabrication/rolling stresses at 450 C, amplified by asymmetric sections, mixed thin/thick material in one assembly, and thin flat panels.

ASTM A384/A384MASTM A385/A385MISO 14713-2:2020

Full guide — causes, remedies and clause references
Galvanized bracket with a grey-green zinc-rich paint repair applied around a drilled hole, with a paint run visible below it
Grey-green zinc-rich paint patches, bright soldered areas, or matte metallized zones within the surrounding hot-dip coating.
ACCEPT

Touch-Up & Repaired Areas

Also called: repair patches · cold galvanizing spots

Why it happens. Legitimate renovation of bare spots or transit damage using ASTM A780 methods: zinc-alloy solder, zinc-rich paint, or thermal spray.

ASTM A780/A780M-20ASTM A123/A123M-24ISO 1461:2022

Full guide — causes, remedies and clause references
A handheld coating-thickness gauge held probe-down against a bright galvanized folded steel section, its display reading 39.2 — the coating looks completely normal to the eye
None. That is the whole point of this entry — coating thickness has no appearance. A thin coating on non-reactive steel looks bright, smooth and entirely normal, and no amount of looking will separate it from a conforming one. It is found with a gauge, a magnetic thickness meter or a cross-section, or it is not found at all. This is the one condition in the gallery you cannot photograph: the picture here is an instrument reading, because that is the only honest way to show it.
REJECT

Low Coating Thickness

Also called: thin coating · under-thickness · below grade

Why it happens. The zinc-iron reaction never ran long enough to build the coating.

ASTM A123/A123M-24ISO 1461:2022

Full guide — causes, remedies and clause references
Galvanized surface where the bright free zinc has flaked away across the centre, exposing the darker smooth zinc-iron alloy layer beneath, with the remaining zinc surviving around the edges as chalky islands with jagged boundaries
Flat patches where the bright free zinc has come away and left the darker, duller zinc-iron alloy layer showing beneath. The trap is that it barely looks like flaking: the free zinc layer is only tens of microns thick, so what it leaves is a change of TONE with an angular boundary, not a lifted flake casting a shadow. Look at texture rather than relief — the shed area is smooth and uniform where the surviving zinc is chalky and granular, and that difference is two materials, not one. In worse cases the coating sheds in visible flakes or lifts under a blade.
REJECT

Zinc Flaking / Poor Adhesion

Also called: peeling · delamination · coating shedding

Why it happens. The coating never formed a sound metallurgical bond to the steel.

ASTM A123/A123M-24ISO 1461:2022

Full guide — causes, remedies and clause references