While it is perfectly normal for bricks to have a slight variance in colour, this is different than brick stains. All care should be taken during construction to prevent staining occurring; however, this is not always possible. Stain removal depends on the cause of the stain.
The Brick and Blocklayers Federation recommends that you consult your bricklayer or brick supplier before attempting stain identification and removal.
The types of stains you may see on masonry brick products are:
Light-coloured clays often contain vanadium salt that are generally colourless but under certain conditions may appear as yellow, green or reddish-brown discolouration of the brick. Vanadium stains are neither permanent nor harmful and do not indicate a defect in the brick.
This stain occurs characteristically along the edges of grey or brown clay bricks. It appears as a dark- blue brown discolouration.
COPPER AND BRONZE STAINS
Sometimes masonry (brick) veneer may be in close proximity to metals such as copper or bronze. Water washing over these metal surfaces can result in a bluish-green stain appearing on the surface of the bricks.
IRON OXIDE (RUST)
Rust can be the result of using hydrochloric acid incorrectly on brick units.
Common around domestic fireplaces but can also be an issue with fire damaged buildings.
Hydrocholoric acid should not be used on clay or concrete masonry brick units unless specifically advised by the product manufacturer or importer.
The Brick and Blocklayers Federation recommends that bricklayers familiarise themselves with the use of the following products:
Dricon – Concrete Treatment http://www.firth.co.nz/dricon/liquids-and-additives/concrete-treatment/
Guardit – Green Acid remover https://www.horizoninternational.co.nz/guardit-green-acid-wash/
Read the next section here: Efflorescence