Efflorescence is caused by soluble salts in building materials, or soluble salts transferred into building materials by water, being drawn towards a drying surface by the movement of water. At the surface of the building material, the water responsible for the transportation of the salts evaporates leaving behind the salts as a surface deposit.
Efflorescence can occur in new buildings when calcium hydroxide from the cementitious mortar or concrete is carried in solution to the surface of the building and then this combines with atmospheric carbon dioxide to form a white deposit of calcium carbonate.
Efflorescence can also occur in old buildings, although in such cases the origin of the salts is often obscure as they may have derived from activities that have long since been removed. For example, the use of coal-burning space heaters could produce sulphur bearing gases that could attack some stone types such as limestone. Another source of salts within building materials is via percolation from the ground.
Efflorescence can often result in damage caused by salt crystallisation leading to the breakdown of mortars and renders or the ‘blowing’ of the surfaces of brick and blockwork.
Assessment of the presence of salts within building materials requires careful sampling. Samples can be obtained from the surface in the case of visual salt crystallisation or via incremental drilling samples to obtain a profile of the salt levels within the building fabric. Analysis can then be used to determine the nature of the salts and the levels of the salts within the building material. Thus the information obtained can be used by conservators in deciding what part salt crystallisation may have played in the deterioration of the building fabric.
Sandberg has undertaken numerous assessments of this nature including those resulting from our specialised commission for English heritage.
Some of the projects we have been involved with include:
- Kenilworth Castle
- Southwell Minster
- Iona Abbey
- The Palace of Westminster
- York Minster
For more information contact our in-house expert: