How to repair welds and cuts in galvanized steel step by step

Hot-dip galvanizing protects steel for decades, but as soon as a piece is welded, cut, or drilled on site, the zinc coating disappears in that area. That bare spot is where rust begins, and from there it spreads beneath the healthy galvanizing. The good news: it can be repaired in a few minutes with a zinc-rich coating.

Why you must always repair it

Welding heat burns off the zinc within a few centimeters around the weld bead, and spatter leaves steel exposed. Standards ISO 1461 and ASTM A780 expressly permit repair with zinc-rich paint, provided the product has sufficient dry film zinc and is applied at the correct thickness.

Step by step

1. Let the weld cool and remove slag and spatter with a wire brush or disc.
2. Sand or brush until the steel is bright, overlapping the healthy galvanizing by about 2–3 cm.
3. Degrease with xylene and let dry.
4. Shake well the product. If using the spray, shake for at least 1 minute until you hear the ball rattling.
5. Apply 2 coats crosswise, allowing 30–60 minutes to dry between them. For structural repair, a dry film thickness of about 105 microns is recommended.

Spray or tin?

For spot welding, fasteners, and cuts, the GALVANOL Spray 500 ml is the most convenient option: there is no need to mix it or clean brushes. For many meters of weld bead or an entire structure, a tin of GALVANOL 1 kg or GALVANOL 2 kg with a brush provides better coverage and is more economical.

Errors to avoid

• Painting over slag or loose rust: the zinc will not make contact with the steel.
• Applying only one thin coat: it will not reach the thickness required by the standard.
• Failing to overlap the healthy galvanizing: a weak line will remain right at the edge.

GALVANOL complies with ISO 1461 and ASTM A780 as a hot-dip galvanizing repair coating, with 96% dry film zinc.