If the galvanized product does not meet all of the requirements of the specification, it must be repaired or rejected along with the lot it represents. When repair of the product is allowed by the specification or bare spots are present, the galvanizer is responsible for the repair unless directed otherwise by the purchaser. The specifications allow for some retesting of products that represent lots or retesting after the lot has been sorted for non-conformance. The coating thickness of the repaired area must match the coating thickness of the surrounding area. However, if zinc-rich paint is used for repair, the coating thickness must be 50% higher than the surrounding area, but not greater than 4.0 mils because mud cracking tends to result when the paint coating is too thick. The maximum sizes for allowable areas that can be repaired during in-plant production are defined in the specifications as summarized below.
Maximum Size of Repairable Area
ASTM A 123/A 123M:
- One inch or less in narrowest dimension
- Total area can be no more than 0.5% of the accessible surface area to be coated or 36 square inches per piece, whichever is less
ASTM A 153/A 153M:
- The bare spots shall have an area totaling no more than 1% of the total surface area to be coated, excluding threaded areas of the piece
ASTM A 767/A 767M:
- No area given
- If the coating fails to meet the requirement for finish and adherence, the bar may be stripped, regalvanized, and resubmitted
- Damage done to the coating due to fabrication or handling shall be repaired with a zinc-rich formulation
- Sheared ends shall be coated with a zinc-rich formulation
Any repairs made to galvanized products must follow the requirements of ASTM A 780, which defines the acceptable materials and the required procedures. Repairs are normally completed by the galvanizer before the products are delivered, but under certain circumstances, the purchaser may perform the repairs on their own. The touch-up and repair materials are formulated to deliver an excellent color that matches either brightly coated, newly galvanized products or matte gray, aged galvanized products. Materials used to repair hot-dip galvanized products include zinc-based solder, zinc-rich paint, and zinc spray metallizing, and are explained in the following sections.