What is mill scale and why should it be removed prior to welding or painting?

Mill scale is a thin, brittle layer that naturally forms on steel during the hot‑rolling process. While it acts as a temporary protective barrier against atmospheric corrosion—useful for storage and transport—it becomes a problem once the steel reaches the workshop.

If mill scale isn’t removed prior to welding, it can contaminate the weld puddle and significantly weaken the finished joint. On surfaces intended for painting, mill scale prevents proper adhesion. Even if primer and paint initially appear sound, the underlying scale will eventually lift, causing the coating to flake and fail prematurely.

At largo, we remove all mill scale before any fabrication or finishing begins. This ensures stronger welds, longer‑lasting coatings, and a final product that delivers reliable performance for many years.