Weld cleaning – what’s that white powder?

The white powder that occurs after weld cleaning is often a residue from the leftover acid that has not been fully neutralised during cleanup. While initially the work looks clean, over time remaining Phosphoric Acid can combine with contaminants in the air, and phosphate salt crystals can form. These crystals are white, make the metal surface look powdery, and can be difficult to remove.

To prevent the crystals from forming, all traces of any acidic fluids must be removed from the work. Simply rinsing with water does not achieve this as the water just dilutes the acid. Even wiping the work thoroughly with a wet cloth often does not work, because the water quickly becomes acidic, and re-contamination of the metal surface occurs.

The easiest way to remove white residue once it has formed is to start the cleaning process again. Re-clean the surface with acidic cleaning fluid, then neutralize the surface with an alkali ensuring adequate neutralizer has been used, and no acid remains on the surface. Wipe dry with a clean cloth and this should prevent the white powder from re-appearing.

We recommend the Cougartron CGT-N1 neutralising fluid to neutralise any phosphate base acid including CGT-550. This is generally applied with a spray applicator and then wiped off with a clean microfibre cloth.