As we have been dealing in the past weeks with problems related to facing bricks I thought this week we could provide details on a situation that we see often occurring in ceramic facing bricks, even though that is only an aesthetic defect without major consequences for the external wall this is not always so, as we will see later.
Efflorescence’s are deposits of crystallized salts that settle on the surface of the bricks in the form of spots, and very often are of a white colour.
We should make a distinction here, between efflorescence’s, which are surface deposits and the criptoefflorescence’s, which are deposits inside the pores of the brick. This latter one is more destructive, because normally increase its volume inside the material, consequently generating surface tensions on the material and forcing the pore to open up allowing water, ice and pollution in the material slowly and gradually, destroying it.
How and why efflorescence occur?
Salt deposits are formed by the migration of soluble salts present in the interior of the brick, it travel through the pores of the material, and accumulate itself on the surface or in the pores immediately below the surface once the existing water evaporates. Since the saline solution exceeds its saturation point it is precipitated in the areas of maximum evaporation and that is normally on the outer surface of the brick wall.
The formation of salts can be internal or external. Salts can be found in the brick itself, i.e. in the clay used for the fabrication of the brick, which contains water-soluble compounds during the heating process that take place in the kiln, impregnated due to the fumes and gases circulating inside the furnaces. The salts in the mortar, are usually found in the aggregates, in the cement or in the chemical additives used. From past experience when sand is extracted from quarries near to the coast, (incidentally, now days it is forbidden by law to extract or remove sand from Spanish beaches) and sometimes directly from the ground when no damp proof course is used.
The salts that appear on surface of the brick usually occur due to the presence of sulphates and carbonates such as sodium, potassium, calcium etc whose composition is different from the salts contained within the brick.
Type of damage that we can find on facing brick walls due to efflorescence’s.
We could classify the type of efflorescence depending on the different manners that manifest themselves:
Category 1: Salts which are deposited on the brick surface, highly soluble in water, of whitish, appearance, usually take the form o a fragile veil and normally are located in the centre or edges of the brick walls, also covering the mortar joints. They usually appear in the top quarter of the buildings as this part is often more exposed, at the base of the wall and around window sills. They are very abundant on recently built buildings. They usually manifest themselves in spring when the wind and sun dry the brick wall after a wet period in winter.
Category 2: Criptoefflorescence’s, can be determine to have happen when we see large amounts of bricks that have parts that have chipped off or major amounts of bricks have tended to opened up in layers by as much as few millimetres. They usually occur in North of Spain or in buildings very close to the coast. Here on Cost Cálida and Costa Blanca is rare and is not seen often.
Category 3: When we can observe dark brown or black spots appearing on the bricks (usually brown pigmented) and on the mortar joints. This peculiar colour is due to the colour of the brick itself as the clay it is pigmented with manganese dioxide.
Category 4: When we can distinguish spots of greenish-yellow. This kind is very rare, so rare in fact that I have never seen any in Spain.
The factors involved in the appearance of efflorescence on a brick wall could be due to:
Efflorescence can occur when we have a relatively low temperature condition with great presence of moisture and salts in suspension within the brick and we also have a difficult evaporation when they are subjected to wind and sun that may cause a rapid evaporation.
The harmful effect of air pollution: Yes air pollution is harmful not only to our lungs but also to brick walls so it is often seen its consequences in areas contaminated by industry, car pollution, etc and it is due to the presence of sulphur dioxide from burning fuel and then these fumes get in contact with rainwater and convert itself in sulphuric acid, reacting with components of the mortar or the brick and finally forming efflorescence.
Category 5: Are normally appreciated as streaks of brown colours on the surface of the bricks and the mortar joints. Are rare and usually occur in bricks which have been submitted to very high temperatures in the kilns.
Category 5: White deposits found on the surface in the form of trails normally very difficult to dissolve with water alone and when mix with hydrochloric acid tend to effervesce. They are extremely difficult to remove. Some times are seen on the Costas after a long damp period.
We will continue next week analysing techniques to prevent damages due to efflorescence and how to remedy the damages when they have occurred.