Construction Welder Question:

Unless welding is performed with a very low current, a concave dip, called a crater occurs at the end of a weldment.

This crater results from the force of the arc and the contraction of melted metal when it cools and solidifies. The size of each crater relates directly to the welding current. Craters are not desirable because they cause a welding defect due to slag wrapping.

Crater welding is one method used to fill craters. It requires regular welding current. There are control sequences that allow you to switch to a crater filler current.