The Cleaning of Brick and Clay Masonry in the UK

The Basics of Brick Cleaning in the UK

The cleaner the bricklayer leaves the wall, the easier will be the cleaning task. The majority of the mortar residues and smears should be cleaned before they set hard. However, in most cases some additional cleaning will be required to completely remove the mortar residue. Cleaning techniques may involve high-pressure water jet equipment or hand methods. Whatever technique is used, the following requirements are observed to ensure additional staining problems are avoided. Test Areas Testing in one or more small areas is the safest way to determine the correct technique and chemical solution to remove mortar residues. This must occur well before final cleaning, as it will usually not be possible to assess the effectiveness of the test brick clean until the masonry dries. Clean Soluble Salt Deposits First Efflorescence, a white ‘fluffy’ deposit, cannot be removed by water or acid. Dry brushing to remove the efflorescence before washing is recommended. If efflorescence is wetted, the salts go into solution and are drawn back into the brickwork and will reappear as the masonry dries. Efflorescence will eventually disappear through natural weathering. Vanadium salts produce a green or yellow efflorescence or stain (mainly seen on cream and light coloured clay bricks). Hydrochloric acid will make these stains much worse and may make them impossible to clean. Mild vanadium stains may be treated with sodium hypochlorite (household bleach). Spray or brush on dry brickwork and leave until the stain disappears, then rinse off. Proprietary mould cleaners containing sodium hypochlorite and sodium hydroxide can be used as above and have been found very effective. Proprietary brick cleaners may also be effective and should be used only according to the manufacturer’s instructions. Proprietary cleaners usually contain acids that must be neutralised after use with a solution of 15 grams of washing soda per litre of water. More than one chemical application may be required and the walls should be rinsed thoroughly after each treatment.

High Pressure Brick Cleaning

High-pressure water washing is now common for cleaning brickwork. If used the pressure is kept below 1000 psi (7000 kPa), the nozzle must be kept 500 mm from the brick face and the nozzle must be a wide fan jet type with an angle of 15 degrees. The following practices must be observed: • Cleaning should not start until the mortar has hardened. • Hard lumps or persistent smears should be removed by hand. • Mask adjacent materials. • Do not apply with the high-pressure sprayer. Use a low-pressure spray or broom it on. • Clean from top to bottom in small sections. •Work in the shade, ahead of the sun, if possible. • WE DO NOT USE EXCESSIVE PRESSURE OR GET TOO CLOSE, as this will damage the face of the brick and the mortar joint. Mortar joints that are no longer smooth with sharp edges is a clear sign of excessive pressure. Excessive pressure is used to make cleaning faster; it does not do a better job of cleaning.

Saturate the Wall Surface

Failure to completely saturate the surface of the wall is in itself a major cause of cleaning stains. Cleaning solutions containing dissolved mortar particles and acids will be drawn into a dry masonry wall, causing staining. Furthermore, saturating the surface of the wall keeps the acid solution on the face of the masonry where the mortar smears are present. It is not true that face saturation weakens the acid and slows the cleaning. Water should be trained on the wall until the brick suction is exhausted. The area to be cleaned must be saturated as well as all brickwork areas below. If the wall appears to be drying on the surface, reapply water until ready to apply the cleaning solution. Recommended acid strengths are based on application to a surface saturated wall. Note: This point must be strictly adhered to for bricks manufactured in Queensland. Their raw materials contain large amounts of iron oxide and failure to saturate the surface of the wall allows acid solutions to react with the iron oxide and create severe iron oxide staining. Failure to saturate the surface of the bricks manufactured in other parts of Australia can also lead to the acid reacting with iron oxide but to a much lesser degree. This form of staining is known as acid burn and is particularly visible on light coloured bricks. Acid absorption into bricks can also lead to vanadium and manganese staining. t