Efflorescence

Removing Efflorescence from Brick

What Is Efflorescence?

Efflorescence is a crystalline, salty deposit that can occur on the surfaces of bricks, masonry or concrete. It is generally a white-grey colour with a powdery appearance. Although efflorescence may not be a risk to the structure of your property, it affects the appearance of a building, particularly it features coloured concrete or brickwork.

Causes of efflorescence

Efflorescence is caused by water-soluble salts and other water-dispersible materials that come to the surface of concrete, bricks and mortars on both internal and external walls. 

There are a number of potential causes, including:

•   Low temperatures.

• Moist conditions.

•  Condensation.

• Rain 

• Water added to the surface of fresh concrete to aid the troweling process.

• Groundwater.

  Three conditions must exist for efflorescence to occur:        

• Water-soluble salts must be present.

• Moisture must be available to transform salts into a soluble solution.

• Salts must be able to move through a material to its surface. The moisture will then evaporate and cause the salts to crystallize, resulting in efflorescence.

  Water moves and migrates through capillaries in  masonry, brickwork or mortar carrying salts to the surface. The fewer capillaries there are, or the higher the density of the material, the more difficulty the water will have in passing through to the surface. The higher the porosity of the material, the greater the likelihood of efflorescence occurring. As salt deposits are left behind by the evaporation of water, humidity levels influence the appearance of efflorescence.Low humidity can result in the evaporation of water prior to reaching the structure's surface, which means that the salt deposit remains unseen. High humidity can result in slower evaporation and hence more opportunity for growth of the deposits, therefore, contacting a professional contractor will help minimise the humidity inside the capillaries by sealing the surface.

  Preventing efflorescence

Steps can be taken to prevent or limit the spread of efflorescence. For example, in their natural state sand and gravel may have been associated with salt-bearing water or soil. This can lead to efflorescence unless the salts are removed by washing. Mixing-water used for mortar or concrete may be taken from a natural source which has been in contact with a sulphate-bearing soil. In this instance, efflorescence can be reduced by using a low water-cement ratio mix for concreting.Clay products such as building bricks and face bricks may also contain soluble salts. To prevent or reduce this, the clay can be washed during the manufacturing process, and a barium salt. In terms of site storage, bricks should be kept off the ground in a dry place so as to prevent dampness or the absorption of moisture.

Removing efflorescence

There are a number of methods for removing efflorescence effectively.Calcium hydroxide can be removed before it combines with carbon dioxide by either pressure washing or wet-scrubbing which puts it in solution with water and allows it to be rinsed away. Fresh water should then be applied by using an air jet or wet vacuum so that the structure isn't left with residue on the surface.Efflorescence, once it becomes insoluble, is more difficult to remove. A mild acid solution can be applied, often using muriatic acid which has been diluted from full strength. After acid washing, the surface should be thoroughly flushed with water and neutralised with baking soda or an equivalent form of sodium bicarbonate. It is important to consider the implications of using acid on the structure surface, which can erode mortar and discolour brickwork.If the efflorescence is older than of months, light sandblasting can be used.      

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