Lack of fusion

Excessive penetration

Excessive convexity

Under cut

Deposit additional weld metal to increase throat thickness

Deposit a thin stringer bead at the top of weld

Correct diameter of electrode as per metal thickness

Ensure correct angle of bevel and required root gap

By grinding out

By chipping hammer and wire brush

Blow of full weld deposit and reweld

By diamond point chisel

Excessive speed of welding

Long arc length

Less current

Wrong selection of electrode