Efflorescence up close

What are the causes of Efflorescence?

It is important for developers, architects and bricklayers to understand the causes of efflorescence and how to prevent it. Below you will find a concise guide outlining the definition of efflorescence, how to identify it, causes, how to minimise the risk.


It is identified by the deposit of soluble salts on the surface of brickwork after the evaporation of water.

How to Identify Efflorescence on Brickwork

It is easy to identify by the unappealing white staining on the surface of brickwork. Standard cases of efflorescence is evident in new builds, however, in rarer cases efflorescence can prove to be quite harmful or toxic.

Efflorescence on Brick

Efflorescence on Brick

What are the causes of Efflorescence in Brickwork?

Most commonly it is derived from soluble salts in clay bricks, sand used in mortars, cement and detergents such as plasticisers. To a lesser degree, evidence of efflorescence can be from other sources.

Clay Bricks

The most common salts in clay are sulfates of calcium, magnesium, potassium and sodium. In days gone by, ferrous sulfate was more common and may have been responsible for rusty stains on mortar or brick.

Mortar Sands

It is strongly advised to not use sea sands in mortar as it contains many harmful salts. Generally, most sands come from river beds or pits and contain not so many salts.


Slag cements can contribute to the evidence of efflorescence. This is because of their appreciable quantities of sodium sulfate. In Ireland, we commonly use Portland cement which is very low in soluble salts.


Plasticisers is a detergent commonly used in mortars. It is important to use properly formulated proprietary mortar plasticisers which have a very low soluble salt content.

Other Sources

Often efflorescence can be a factor during the storage phase of a project. All bricks and associated products should be stored in a dry sheltered space, elevated from the ground. It is imperative to eliminate any contact with surrounding soil during storage.

How to minimise the risk of Efflorescence

The most obvious way is by reducing the amount of water penetrating the brickwork at all phases of the construction process

Good Design Details

Overhanging verges, eaves, copings and cills can help prevent the brickwork from becoming saturated. Details which guide water away from brickwork is good practice

Site Practice

You should always elevate Bricks, mortars and adhesives from the ground during storage. Any newly built brickwork should be protected from saturation for at last 7 days after bricklaying.

How to treat Efflorescence

You should allow it to wear away naturally, particularly on external surfaces. Internally, you can try small test patches using mists of water. This might be a good option reducing the risk of patchiness.