Corrosion of embedded metalwork
The corrosion of embedded metalwork (especially unprotected steel and iron) such as wall ties, cramps, straps, fixing bolts, beams and lintels can damage and disrupt brickwork. When steel or iron rusts, it expands in size. This expansion can exert forces on brickwork which can cause spalling, cracking and the opening up of mortar joints (in severe cases, bulging and collapse of brickwork may occur). These defects can allow more moisture to the embedded metalwork speeding up the corrosion of the metal.
Brickwork can also be stained by corroding metals. Iron and steel can cause orange through to dark brown rust staining. Copper, brass and bronze green staining and lead white/grey staining
The cleaning of brickwork may be carried out to remove harmful deposits and coatings or for purely aesthetic reasons. However, cleaning is not always advantageous or even necessary especially with regard to historic brickwork. If the decision to clean is taken, then the system chosen to be used should be selected with care after site specific analysis of the brickwork to be cleaned along with the type of soiling requiring removal. Site trials should always be carried out and the work undertaken by skilled operatives
Inappropriate cleaning methods carried out by unskilled operatives can cause serious and irreversible damage to brickwork which is not only unsightly but can also make it more vulnerable to accelerated decay.
All three of the main methods of cleaning ( abrasive cleaning ,water based cleaning and chemical cleaning) can all cause damage if carried out incorrectly.
A major risk with abrasive cleaning is that the fire skin surface of the brick can be completely removed, especially if air abrasive (often called grit or sand blasting) methods are used where a too hard an abrasive is used at too high a pressure. Other risks include gun shading and surface pitting.
Water cleaning where high pressures are used, such as in jet washing can cause similar problems as abrasive cleaning. Other problems caused by water cleaning, especially when large volumes of water are used at either low or high pressures include the mobilisation of salts within the brickwork, water penetration which may initiate other forms of deterioration including the rusting of embedded metalwork and the rotting of built in timbers. Water based cleaning should never be undertaken when there is a risk of frost.
Chemical cleaning is usually carried out with acidic and/or alkaline based cleaners. Both have the potential to harm brickwork. Lime rich mortars can be seriously attacked and dissolved by acidic based cleaners and alkaline based cleaners have the potential to deposit harmful soluble salts within the brickwork. Blotching, variable cleaning and chemical staining can occur with both types and the water used to pre-wet the surfaces prior to the application of the cleaner and to rinse the cleaner from the surface can cause the same problems as water cleaning.
All buildings and structures at some point in their lifetime will require repairs and maintenance. When this is carried out correctly it should not only enhance the building or structure but also prolong its life. However, inappropriate repairs and maintenance may not only be disfiguring but may even be harmful and hasten deterioration.
Inappropriate repairs and maintenance include unnecessary or poorly executed repointing, patching of decayed bricks using strong mortars or their replacement using ill-chosen bricks and the application of unsuitable coatings such as paints, water repellent treatments and renders.
One of the main and most common problems are caused by the use of incompatible materials, such as the use of strong impermeable portland cement mortars for carrying out repointing, rebuilding or repairs to a building or structure constructed using soft bricks and/or lime based mortars. The use of these cement mortars can actually cause or aggravate brick decay and deterioration.
Many buildings and structures constructed in the late 19th and early 20th centuries were built using cement mortars however, these cements were considerably weaker than the cements produced nowadays. The same can also be said of lime and therefore analysis of the existing mortar and the correct selection of the replacement mortar should always be carried out.
Other inappropriate repairs can be caused when undertaking structural repairs, especially if materials or areas are created within the structure that are much stiffer than the surrounding materials or areas.