Repairing Hot Dip Galvanizing

 

When severe damage to the galvanized coating has occurred during welding or as the result of rough handling in transport or erection, protection must be restored.

Small areas of the basis steel exposed through mechanical damage to galvanized coatings, are protected from corrosion cathodically by the surrounding coating and may not need repair, depending on the nature of the product and the environment to which it is exposed. Small exposed areas normally have little effect on the life of the coating as discussed under Cathodic protection’.

 

Repair Methods

The coating repair methods detailed below are in accordance with AS/NZS 4680 section 8 - Repair after Galvanizing.

They include:

Zinc rich paints 

The application of an organic zinc rich paint is the most rapid and convenient method of repair.  The paint should conform to AS/NZS 3750.9 'Paints for steel structures - Organic zinc-rich primer' applied in two coats by brush to provide a total film thickness of a minimum of 30μm more than the local coating thickness requirements in AS/NZS 4680 and should contain not less than 85% zinc in the dried paint film.

Where colour matching is required aluminium paint may be applied over the hardened zinc rich paint.

 

Zinc metal spraying

In certain circumstances, by prior agreement, zinc metal spraying may be used as a method of coating repair.  The damaged area must be grit blasted to Class 3 followed by zinc metal spraying to a coating thickness equivalent to that of the undamaged coating, and seal coated using an aluminium vinyl paint.

 

For further details on Repair please see the FAQ page