Which coating should be applied to bare metal before plug welding, if applicable?

• A. Weld-through primer
• B. Anti-spatter
• C. Zinc coating
• D. Rust inhibitor

Answer: (A)

Coatings around the weld area can change heat flow and the quality of the weld, so choosing a coating that is compatible with welding is key. Weld-through primer is designed specifically for this situation: it can stay on the bare metal in the weld area and still be welded through. It melts away and allows fusion, while providing corrosion protection on the hidden side once the joint is formed. This makes it appropriate to apply when a coated surface would otherwise be left bare, as long as the repair procedures permit it.

Anti-spatter is intended to protect nearby surfaces from spatter, not to prepare the weld surface itself. Leaving it on the weld area can interfere with fusion or leave residues that complicate the weld, so it isn’t used as the weld surface coating for plug welding.

Zinc coating (galvanizing) creates a barrier that can cause porosity or other weld defects if left in the weld zone; it’s typically removed or avoided at the weld site rather than used as the weld-through coating.

Rust inhibitors aren’t meant for the weld zone because they can burn off, contaminate the weld, and don’t provide the needed corrosion protection for the joint after welding.

So, using a weld-through primer is the best choice for coating bare metal before plug welding when applicable.