Quick answer: Welding and cutting destroy or damage zinc coatings around the heat-affected area. The repair must begin after welding is complete and the steel has cooled. Slag, spatter, oxide, burned coating, salts, oil and loose material must be removed; the repair material must contact prepared metal and reach the specified DFT.

This page is intended for fabrication shops, erection crews and inspectors. It covers field and workshop touch-up of welds, cut edges, drilled holes and local galvanizing damage.

It does not replace welding procedures, hot-work safety requirements or the governing galvanizing repair specification.

Why Weld Areas Need Repair

Welding heat burns or oxidises zinc around the joint. Cutting, grinding and drilling expose bare steel. Transport and erection can damage adjacent coating.

Unprotected weld toes, cut edges and sharp projections are local corrosion sites and often receive lower coating thickness than flat surfaces.

Correct Work Sequence

1. Complete welding, cutting and dimensional correction.
2. Allow the steel to cool.
3. Remove slag, spatter and sharp projections.
4. Inspect the full heat-affected and damaged zone.
5. Degrease and remove salts.
6. Mechanically prepare to the required standard.
7. Remove dust and confirm dryness.
8. Apply the approved zinc-rich repair system.
9. Measure DFT and record acceptance.

Do Not Coat Before Welding

Do not place ordinary coating in the weld zone unless the welding procedure specifically allows a weld-through primer. Coating fumes, contamination and weld quality must be controlled.

A commercial cold galvanizing compound should not be assumed to be a weld-through primer.

Preparation of Welds and Cut Edges

Remove visible slag, flux residue, spatter, heat tint, burned coating and rust. Smooth sharp burrs and feather the boundary onto sound surrounding coating.

Clean pits, weld toes, undercuts and inaccessible corners. Salt or oil must be removed before final mechanical preparation.

Selecting the Repair Material

ASTM A780/A780M recognises zinc-rich paint, zinc solder and sprayed zinc as repair categories. The project specification determines which is acceptable.

For a paint repair, confirm dry-film zinc content, required DFT, application method, cure, topcoat compatibility and appearance requirement.

Application

Power-mix dense zinc-rich material. Stripe coat weld toes, cut edges and corners where required. Apply controlled coats rather than one excessively thick layer.

For ROVAL, follow the current manufacturer TDS and standard approximately 80 μm total DFT system unless a project-specific repair thickness governs.

Overlap and Boundary

The repair should extend onto sound surrounding coating sufficiently to create a continuous protected boundary. The overlap must be clean and prepared for adhesion.

Do not leave a narrow uncoated line between the repair and original galvanizing.

Inspection

Check full coverage, DFT, adhesion where required and absence of pinholes, dry spray, runs or cracking. Verify bolts, underside edges and back sides of welds.

Record weld identification, repair area, preparation, product batch, environmental conditions, coat times and final readings.

Duplex and Topcoated Systems

If the structure will receive a later paint or powder-coating system, repair-material compatibility must be agreed before use. Some zinc-rich repairs can create topcoat bubbling, adhesion or recoat-window problems.

Coordinate the galvanizer, fabricator, coating applicator and inspector so the repair is compatible with the final system.

Safety

Follow hot-work controls, ventilation, respiratory protection and SDS requirements. Do not apply solvent-borne coating near active welding or ignition sources.

Remove zinc-containing dust and coating waste according to site environmental procedures.

Frequently Asked Questions

How much of the heat-affected area should be repaired?

Repair all damaged or uncoated material and follow the project limit and boundary requirements.

Can the coating be applied immediately after welding?

Only after the steel is cool, safe and fully prepared.

Is grinding alone sufficient?

Not if oil, salts, dust or inaccessible oxide remain. The full preparation specification must be met.

Can any zinc spray be used?

No. The repair material must meet the project requirement for zinc content, thickness and performance.

What if the structure will be topcoated?

Confirm compatibility and recoat procedure before selecting the repair material.

Technical References

1. ASTM A780/A780M-20
2. American Galvanizers Association – Repair methods
3. American Galvanizers Association – Duplex repair compatibility
4. ROVAL Downloads

Technical notice: This guide does not replace the current manufacturer TDS, SDS, contractual coating specification or site-specific engineering assessment. Confirm the latest documentation before use.