How and why efflorescence occur on facing brick wall | Part 2

Las week we did analyse the effect of efflorescence on facing bricks. We discussed the different sources of damages and how this anaesthetic consequence happens.

 

So let’s recapitulate how the salts cause what some architects considers building failures.

 

Salt deposits are formed by the migration of soluble salts present in the interior of the brick, through the pores of the material, accumulating on the surface or in the pores immediately under the surface when the existing water evaporates. As the saline solution exceeds its saturation concentration it is precipitated in the areas of maximum evaporation.


The formation of salts can be internal or external. The salts can be found in the brick itself actually in the clay, which contains water-soluble compounds during the furnace process, where the clay it is e impregnated with fumes and gases circulating inside the furnaces, in the mortar (in the aggregates, cement or chemical additives) and sometimes on the ground.


It is on the surface where salts usually accumulate with greater or lesser presence of sulphates and carbonates (sodium, potassium, calcium ...) whose compositions are different from the salts contained within the brick.


Right, his week we will see what factors are involved in the appearance of efflorescence on a brick and mainly are due to:


Environmental conditions:

When we have a relatively low temperature with greater presence of moisture and salts in suspension due to the difficulty of evaporation and it is subjected to wind and sun which cause a rapid evaporation.


To the effect of air pollution:

In contaminated areas by industry, car traffic, due to the presence of sulphur dioxide from fuel burning which then get in contact with rainwater converting itself into in to the frightening sulphuric acid which will react with the components of mortar or brick, forming efflorescence.


Pores geometry:

Curiously enough the geometry of the pores may have an adverse effect on the facing walls:


According to the form of these pores salt deposits will form either inside or on the surface and as we mentioned last week, when efflorescence forms on the brick surface it is an anaesthetic consequence but when it forms inside the brick itself we may have a building failure, anyhow it is obvious that higher porosity means greater capillary suction power of soluble salts from the bricks and mortar or when it is in contact with the ground, due to a lack of damp proof courses.


A higher salt content means an increased migration of the salts if the brick wall is in direct contact with soluble salts from saline soils, industrial land with debris, ash, slag or other types of debris the problem is multiplied. When efflorescence is caused by external contamination we have the most serious and persistent type of efflorescence, so lets avoided.


And lastly and very significantly with the presence of water, without water or moisture we would not have efflorescence:


Without water, there is no efflorescence as it is the medium in which salts travels.

Water is present in the form of rain, or by capillary force. Without water, there is no efflorescence as it is the medium in which salts travels.


Damage prevention.

The firs method is to avoid efflorescence is to prevent the brick work from being contaminated by soluble salts that come from contaminated soil by industrial products, debris or organic or inorganic waste.


It is advisable that the brick work should not become exposed to damp or water filtration due to leaks from installation pipes or from different wet areas. If efflorescence does not disappear during the first couple of years we should observe if there are localized spots as it is possible that there may be some water leak from some where.


No need to mention that it is very important to design suitable construction details to prevent water penetration anywhere on the brick wall.


To avoid efflorescence that may happen due to a chemical reaction between mortar and the brick, use lime mortar (cement-lime-sand). To avoid suction of water and salts from the mortar it is advisable to pre-wet the piece and in case of heavy rain, protects the brick that has been recently laid. To prevent the absorption of salts from the ground we should placed brick piles on top of a plastic sheet.


During the execution of the works we must try to not get bricks too wet, especially during periods of heavy rain, so cover the work which have been recently completed and also any brick delivered on site.


The test that is becoming almost compulsory to undertake when using facing brick in Spain is the UNE 67029:1995 EX which determine the amount of efflorescence on the bricks.


Next week we will provide the solution to remove efflorescence from the brick surface depending on the type of salts that provoked it in the first place. 


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