This study is done to obtain the fundamental knowledge on the effects of endothermic materials on the undercut defect of welding, of which information is scarce in international welding literature. Undercut is one of the most crucial problems which decreases the reliability and restricts the many parameters of welding. One reason for this type of defect is excessive current, causing the edges of the joint to melt and drain into the weld, leaving a drain-like impression. Other reasons may be the poor technique used, using incorrect filler metal, small electrode angle, dampened electrode,...