3f2c04aa_ick___Cleaning___Stain_Removal__Description
[Stain] Vanadium Stains [Cause] Often generated by the use of too strong a concentration of hydrochloric acid during the initial cleaning process, or from excessive water penetration. [Removal] Sodium hypochlorite, Oxalic acid, Potassium hydroxide or sodium hydroxide (caustic soda) or Proprietary cleaners. It is best to test the efficiency of these chemicals on a test area to determine the most suitable treatment to use. [Description] 
Light-coloured clays often contain vanadium salt that are generally colourless, but under certain conditions may appear as a yellow, green or reddish-brown discolouration of the brick.
Brick | Cleaning | Stain Removal
Description