Technical Info | ASTM-A780 (Standard Practice for Repair of Hot-Dip)
ASTM-A780

ASTM Designation: A 780 (American Standard Testing Method)

Standard Practice for Repair of Damaged and Uncoated Areas of Hot-Dip Galvanized Coatings

4.2.2 Zinc-Rich Paints - These are usually based on organic binders, pre-mixed and formulated specifically for use on steel surfaces. These Zinc-Rich paints are suitable for repairing damaged galvanized coatings, provided the dried film contains not less than 65% zinc dust by weight. Brite Zinc meets and exceeds this percent. Corrosion resistance and service performance are very dependent on the properties of the paint system, the extent of surface preparation, and skills of individual applicators.

ANNEXES

A2. REPAIR USING ZINC-RICH PAINTS

A2.1 Preparation of the damaged surface will be influenced by the type of paint selected and the anticipated service conditions. Experience shows that in general organic zinc-rich systems are more tolerant of surface preparation. Most organic zinc-rich paints are not critical of climatic or atmospheric conditions for curing. Brite Zinc is an organic zinc compound.

A2.1.1 Surfaces to be reconditioned with zinc-rich paint shall be clean, dry, and free of oil, grease, and corrosion products.

A2.1.2 Where anticipated, field service conditions include immersion, blast clean the surface in accordance with SSPC-SP5, white metal. For less critical field exposure conditions, blast clean the surface to near-white metal, in accordance with SSPC-SP10 (1 to 2 mil (25 to 50 (m) anchor pattern), as a minimum. Where circumstances do not allow blast cleaning, it is permissible to power disk sand areas to be repaired to bright metal. To ensure that a smooth reconditioned coating can be effected, surface preparation shall extend into the undamaged galvanized coating. The method and extent of surface preparation shall be mutually agreeable to the contracting parties.

A2.1.3 If the area to be reconditioned includes welds, first remove all flux residue and weld spatter of a size or type that cannot be removed by blast cleaning by mechanical means, that is, chipping, etc.

A2.1.4 Spray or brush-apply the zinc-rich paint (Brite Zinc) to the prepared area. Apply the paint as recommended by the paint manufacturer in a single application employing multiple spray passes to achieve a dry film thickness to be agreed upon between the contracting parties.

A2.1.5 Take thickness measurements with either a magnetic or electromagnetic gage to ensure that the applied coating is as specified.