Why does my weld have sugaring (stainless)?

Root causes

The back side of a stainless weld oxidising because it receives no shielding gas.

The fix sequence

• purge the back of the joint with argon or apply a backing flux paste before welding
• Change one variable at a time and re-test on scrap
• Re-inspect the finished bead — chisel, brush, look

When to grind it out

Structural or pressure work with visible defects: grind back to sound metal and re-weld — never 'cap over' a defect and hope. For non-critical jobs, judge honestly: a cosmetic defect is a learning note; a fusion or crack defect is a redo.