Overlap is one of the most common weld discontinuities, yet it often slips past visual inspection until after painting or final quality checks. This defect occurs when molten weld metal rolls over onto the base metal without fusing properly, creating a mechanical notch that can trigger cracking and costly repairs. In this article, we break down the causes of overlap—including poor welding procedures, mill scale, and inadequate technique—and outline proven solutions for preventing it. If you’re responsible for welding quality in your shop, this guide will help you recognize overlap and correct it before it becomes a problem.