Stains Due to Metallic Salts
Staining from metallic salts may originate from corroding material, especially from iron, from the bricks themselves, or from the mortar. It can indicate deterioration of the reinforcement or ties leading to cracking and loss of strength in the structure. Manganese gives rise to dark brown or black stains. Vanadium, which can occur in small quantities in some brick types gives rise to a yellowish stain which turns green with exposure.