An Overview of Efflorescence
Efflorescence is defined as “the loss of water (or a solvent) of crystallisation from a hydrated or solvated salt to the atmosphere on exposure to air”.
Efflorescence can occur in both natural and man-made environments and can present itself as either a mere cosmetic issue, known as primary efflorescence, or can be an indication of severe structural damage, referred to as secondary efflorescence.
Primary efflorescence usually occurs as a result of the initial curing process of a cement-like product, thus earning it its name ‘primary efflorescence’.
Primary efflorescence often occurs on brick and other masonry materials including some mortars. It is caused by water moving through a wall, for example, bringing salts to the surface that are not typically bound with the cement.
Secondary efflorescence is so named because it has less to do with the formation of the cement stone and has more to do with the exposure to concrete poisons, such as chlorides.
This type of efflorescence is commonly seen in multi-storey car parks or steel-reinforced concrete bridges.
Saline solutions get produced through a mixture of road salt and water present in the winter months which can then be absorbed into the concrete and begin to dissolve the cement stone.
Some types of cement are more susceptible to chlorides than others so the decision over which cement to use has a large impact on the concrete’s chloride reaction.
Secondary efflorescence is often referred to as concrete’s version of osteoporosis because of the way it weakens its structure.
Both primary and secondary efflorescence can be prevented through the use of admixtures that chemically react with the salt-based impurities and bind them into the concrete. These admixtures are the only way to properly prevent efflorescence.
It is also possible to protect the more porous building materials such as brick by using a water repelling sealant. This sealer will penetrate the material deeply enough to keep the water and salts away from the surface.
A lot of the water repellents available today have a vapour permeable barrier meaning that liquid water, such as rain, are kept out while water vapours from inside buildings etc are able to escape into the outer atmosphere.
Efflorescence can also be removed through the use of phosphoric acid. Once the diluted acid is applied and neutralised with a mild diluted detergent it can be rinsed away well with water and this should remove the present efflorescence. However, if the source problem of the efflorescence isn’t identified and controlled, the efflorescence can reappear.
In instances regarding paving, the efflorescence seen on cement paving stones is usually a build-up of calcium carbonate whereas the efflorescence that occurs on clay-based paving slabs is commonly sodium chloride or, as it is more commonly known, table salt.
The key ingredients needed for calcium carbonate efflorescence to bloom are calcium oxide, carbon dioxide and water but the amount of efflorescence you may find will depend on the amounts in which these ingredients are present as well as the atmospheric conditions which can speed up and slow down the chemical reaction.
There is no set time frame for how long a period of efflorescence will last. Efflorescence can be present for a few weeks or even for a few years.
There is evidence to suggest that damp and shady spots are more susceptible to the development of efflorescence while open and sunny spaces are less adversely affected.
Several manufacturers sell chemicals that removes the efflorescence from the cement but it is difficult to say how long these will last without addressing the underlying issue.
Similarly, a chemical free way to remove efflorescence from your paving or bricks is to regularly brush the concrete and rinse it with cold water. This will help to remove both the soluble and insoluble products of efflorescence and may even speed up the process leading to the permanent disappearance of efflorescence.
Overall, efflorescence is a common phenomenon that is individual with each and every case. It is not harmful but can look unappealing and unattractive. However, over time, efflorescence will gradually disappear.
If you need any more information about the best paving products in the area, get in touch with Minster Paving today.
Call 01865 300252 or contact us online.
NOTE: From our T&Cs
On occasions you may notice white or dark patches appearing on your patio, this is known as efflorescence. This condition can occur with all concrete products that have a high cement content. It is more noticeable when the slabs are dry and is due to deposits of calcium oxide reacting with carbon dioxide. This will disappear with time and generally does not reappear again.
Please note that should there be any other defects other than the above mentioned naturally occurring ones, Minster Paving Ltd should be notified before the paving slabs have been laid. Once the paving slabs have been laid Minster Paving Ltd cannot accept responsibility for any defects or the above mentioned conditions.