Brickwork can be subject to all kinds of discolouration depending on the type of brick and the stain. However, concentrating on efflorescence its necessary to understand what it is and why it happens. There are 3 types of efflorescence, 2 primary and 1 secondary (Gypsum efflorescence). Here we focus on the 2 primary types.
Salt Efflorescence
Mainly occurs when there is excessive contact with water during the bricklaying process. The open pores of the bricks and joints allow water soluble compounds to move to the surface. When it dries the salt crystallises forming white deposits. Different bricks will have varying amounts of porosity so will be affected in different ways.
Salt efflorescence is unsightly but is quite harmless. As salt is soluble in water it can be removed by the rain over time. Lukewarm from a hose can be used to speed up the process, however its important to remember that some moisture maybe drawn back into the brick causing the staining to re-appear. Dry removal can be carried out using just a soft brush.
Lime Efflorescence or Lime Run off
An effect that can come about when excess water flows through cementitious material. This water can dissolve calcium hydroxide (free lime) which is then deposited on the brick face. The calcium hydroxide is a soluble form of lime which is created as Portland cement hydrates.
The source of the lime may be the cement from mortar joints, or it may come from concrete or cast stone elements; for example, a coping above a brick wall or a floor slab built into the brickwork. Lime material washed from mortar joints can be due to a lack of adequate protection against rainfall during construction.
The run-off is often seen from weep holes or fine separation cracks between brick-and-mortar joints. The calcium hydroxide reacts with carbon dioxide in the air producing a hard crystalline formation of calcium carbonate.
It is common for lime run-off to be mistaken for salt efflorescence. The primary differences are that it typically originates from mortar joints rather than the bricks themselves, and it does not disappear on wetting. At an early stage, Lime efflorescence off can be removed very easily using water or brick cleaner but if it is left it will have to be professionally removed with special cleaning products.
Best Practice
Staining of brickwork very often originates from excessive wetting or saturation of recently built brickwork, therefore
- Brickwork should be kept clean and protected from rainfall, snow and contamination.
- Care should be taken to avoid mortar smearing or splashing as the work proceeds.
- Bricklaying should normally cease when the temperature is 3° Celsius and falling and not begin again until the temperature reaches 3° Celsius and rising.
- If overnight frost is likely to occur before the mortar within newly constructed brickwork has fully set, it should be protected with an insulating layer of hessian underneath the polythene. This would normally give some protection to the mortar joints from the actions of overnight frost.
- During periods of hot and dry weather it may be necessary to reduce the initial suction rate of highwater absorption bricks by briefly immersing in clean water prior to laying.
- Where practical, it is beneficial to cover newly built brickwork with hessian sacking during hot days. This will help to prevent the brickwork drying out too quickly before the cement has set and the mortar has sufficiently bonded.
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