Weld Undercut

In continuing our explanation on weld defects we are finishing the series with weld undercut.  Weld undercut may be allowed in some situations.  You must know the code and specification that you are working to in order to confirm the allowance.  Then depending on the allowance you will be required to measure the undercut to determine if it is considered a defect.

Weld Undercut  is a defect that appears as a groove in the base metal directly along the toe.


  • improper gun angle
  • too high welding current
  • poor torch manipulation


How to Prevent the Problem:

  • set proper welder settings
  • control proper push/pull and work angles of torch

 How to Repair

  • add additional weld pass to fill undercut and blend weld.

For information on other weld defects, check out our previous blogs

Lack of Fusion

Incomplete Penetration

Slag inclusion

Weld Crater


Until next week,

Bonnie Pankratz