Cleaning

Safety

Cleaning agents are generally poisonous chemicals and should only be used in accordance with the manufacturers’ recommendations and safety practice data sheet.

Mortar Smears

Although it is preferable for bricklayers to clean their own work progressively, removing mortar smears and stains, this does not usually occur. The most common method of cleaning is high pressure water jet. If mortar smears are heavy, acid solutions or proprietary cleaners are commonly applied. It is in the application of acid, that many problems can occur. Proprietary wall cleaners should be used in preference to acid when there is risk of further staining. Acid or cleaners should not be applied under high pressure and should be washed off using low pressure water. In some cases, an alkaline solution should be applied to neutralise the acid.

White Soluble Efflorescence

White powdery deposits usually result from soluble sodium or potassium salts in the bricks or mortar being drawn to the surface by evaporating moisture. Good detailing which prevents the entry of moisture into the masonry will minimise efflorescence. It is best removed by brushing and then hosing off with clean water.

White Insoluble Calcium Carbonate Stains

White calcium carbonate staining is occasionally present in clay brickwork and common in concrete masonry. The most common mechanism for its occurrence is:

• Moisture enters the external masonry leaf through open topped walls, sills or poorly constructed mortar joints.
• The moisture dissolves calcium oxide in the cement and lime, forming calcium hydroxide.
• A combination of low external humidity and high humidity in the cavity and within the units forces the calcium hydroxide solution to the outer surface of the wall.
• The calcium hydroxide combines with the carbon dioxide in the atmosphere to deposit insoluble white calcium carbonate on the surface.

White staining is occasionally deposited on smooth face dark coloured clay brickwork as a result of incorrect acid cleaning. If insufficient water is used, the products of the acid/mortar reaction are absorbed into the brick surface rather than being washed off. This problem will be more apparent if clay-bearing mortar sands are used. In this case, the clay combines with the calcium and silica residues to yield a very resistant white film.

Green, Yellow or Reddish Brown Vanadium Stains

These stains originate in the clay used to manufacture some bricks and are precipitated at the surface as vanadium sulphate and vanadium oxide. Do not use hydrochloric acid to dissolve these stains, because it will react to form a hard green deposit that is difficult to remove.
The following materials may be effective (with caution and subject to the recommendations of the masonry manufacturer) in assisting in the removal of vanadium stains:

• Potassium Hydroxide
• Sodium Hydroxide (Caustic Soda)
• Oxalic Acid Followed By Washing Soda
• Proprietary Cleaners

Dark Blue or Brown Manganese Stains

Manganese stains result from the manganese dioxide in some dark coloured bricks. The stains usually occur at the edges of the bricks or at mortar droppings. Manganese sulphate or chloride solutions migrate to the mortar joints during drying and are neutralized by the mortar. Insoluble manganese hydroxide precipitates at the mortar and converts to brown Mn3O4 on drying. Manganese coloured bricks should not be cleaned with hydrochloric acid without neutralizing the acid.
The following materials may be effective (with caution and subject to the recommendations of the masonry manufacturer) in assisting in the removal of manganese stains:

• Acetic Acid And Hydrogen Peroxide Solution
• Phosphoric Acid
• Proprietary Cleaners.

Brown Iron Oxide Stains

Iron oxide stains may result from the rusting of steel components adjacent to the masonry or from using hydrochloric acid to clean clay bricks containing iron (acid burn). The stain is usually yellow to brown and can range from light to dark brown, particularly on cream bricks.
The following materials may be effective (with caution and subject to the recommendations of the masonry manufacturer) in assisting in the removal of iron oxide stains:

• Phosphoric acid.
• Oxalic Acid, Sodium Fluoride and Citric Acid Solution
• Proprietary Cleaners.

Waterless Cleaning

Where waterless, chemical free cleaning is required for removal of mould spores, ash, or organic contaminates, pressurized carbon dioxide thermal shock may be used.