What is Efflorescence?

At Access Training our bricklayer courses will train you up to the highest possible standard. However there have probably been instances where you've seen newly built houses or walls with high quality brickwork, only to see white patches unevenly spread over the structure. This is most probably "efflorescence" and this post aims to teach how you can help prevent it in your future work.

So what is efflorescence? It is the formation of (usually white) salt deposits on the surface of brickwork, which causes a change in appearance. Apart from the unsightly appearance and discolouration, efflorescence can sometimes indicate serious structural weakness.

While there is an agreement that it is caused by a multiple of factors being combined with materials, views differ as to which factor is the main cause of efflorescence. It is usually impossible to deduce the exact causes with absolute certainty.

To help prevent efflorescence, some factors to consider are;

Cement: The type/make of cement chosen can influence efflorescence in exceptional cases. Pigments in coloured cement and other admixtures added to the mortar may contribute to efflorescence through their salt content.

Aggregates: These can contribute to efflorescence if they contain soluble salts. Sand contaminated with salt is a major factor, therefore sands in close proximity to the sea are an obvious risk.

Salts: Soluble salt is present in the materials used to make bricks, therefore it is capable of being transported and deposited on the surface as efflorescence.

Water/Cement ratio: Generally a high water-cement ratio encourages the movement of water and salt through the brick, giving rise to efflorescence.

Mortar Constituents: The composition of mortar is of significance. Lime used should be hydrated and free from calcium sulphate. The use of unwashed sand or sand contaminated with salt, or pigments containing soluble salts can also contribute to efflorescence in brickwork.

The following practices may also cause efflorescence;

• No protection from the rain, especially during construction.
• Materials left uncovered on site.
• Lack of drips on cills.
• Poorly filled joints/bad workmanship.