Which type of weld is typically used for repairing metal surfaces?

Fillet welds are commonly used for repairing metal surfaces because they are designed to join two surfaces at right angles to each other, creating a strong bond that fills gaps between the base materials. This type of weld is particularly effective for repairs since it can be applied in various positions and is suitable for joining different thicknesses of metal. The triangular cross-section of a fillet weld allows for good penetration and strength, making it ideal for structural applications and repairs.

In contrast, spot welds are typically used to join overlapping metal sheets at specific points rather than for extensive surface repairs. Plasma arc welds involve a high degree of precision and are generally used in applications that require detailed and complex welds rather than basic repairs. Tack welds are temporary welds used to hold parts together before permanent welding is completed, not for the repair of surfaces themselves. Thus, fillet welds are the most appropriate choice for effectively repairing and reinforcing metal surfaces.