What is Efflorescence?

The term ‘efflorescence’ is used to describe the depositing of soluble salts (in other words, those that dissolve in water) on the surface of finished brickwork. Salts of magnesium, calcium, potassium or sodium may have been present in the clay used to make the bricks or in the sand used to make the mortar.

The most common form of efflorescence is an unsightly but harmless white deposit which does not affect the durability of the brickwork and normally disappears from new buildings within the first few months following construction, particularly if brickwork is unprotected during periods of wet weather.

What are the Sources of Soluble Salts?

The sources of soluble salts Common efflorescence derives mainly from soluble salts that are contained in clay bricks and sands used for mortars but sometimes in other sources, including ground water.

Clay

Impurities in clay raw material from which bricks are made, include various soluble salts. These salts are impossible to remove before bricks are made, and can cause problems of efflorescence and sulphate attack on cement mortar in walls which may be wet for long periods each year in completed buildings.

Mortar sands

Most sands come from pits or river beds, and contain few salts. Sea sands contain many harmful salts, however, and should not be used for mortars unless they have been effectively washed by a reliable supplier.

Cement

Portland cement is the main binder constituent used, and its contribution to efflorescence is minimal. Mainly due to the desire to reduce carbon emission from cement production, alternative binders are used in modern cements and they can contain appreciable quantities of sodium sulfate, which is a common cause of efflorescence

Detergents used as plasticisers

Many detergents contain sodium sulfates and should under no circumstances be used in place of properly formulated proprietary mortar plasticisers (see Section 3.1).

Other sources

Bricks may absorb salts from ashes or the soil on which they are standing or from materials stacked or heaped in contact with them.

How efflorescence in brickwork forms?

Water dissolves soluble salts in the bricks or mortar and holds them in solution.

As the water evaporates and the wall dries out, the solution becomes more concentrated until salts begin to be deposited.

This may occur out of sight within the pores of the brick or on the surface.

Exactly where, when and how much efflorescence will occur is difficult to predict. Because it dependent on complex chemical and physical conditions such as the type of salts, the pore structure within the brick, the rate of drying by wind and sun, and the degree of saturation of the brickwork. The latter is the only condition which we can readily control.

How to minimize the risk of efflorescence in brickwork?

The risk cannot be entirely avoided, as it is not practicable to eliminate all salts from bricks and mortars, or to keep them virtually dry, but it can be minimised by reducing the amount of water penetrating the brickwork.

Design details

Designers can use ‘umbrella’ details which protect the brickwork from saturation. Such details include effective roof verges and eaves, copings and sills to shed run-off water clear of the brickwork below.

They should also avoid details which shed water onto projecting plinths and other features.

Site practice

• Bricklayers and site supervisors are responsible for good site practice.
• Bricks should be stacked clear of the ground on pallets, or by other means.
• Mortar materials should be kept free from contamination.
• Bricks in stacks or on the scaffolding, and newly built brickwork, should be protected from saturation, particularly during the seven days after bricklaying.
• Scaffold boards adjacent to the brickwork should be turned back during rain to avoid splashing causing a band of efflorescence as well as mortar stains.

Choice of bricks

New bricks are tested by manufacturers for the extent to which they are likely to effloresce and bricks are graded on the following scales in terms of the bricks’ exposed surface area:

• Nil : no perceptible efflorescence.
• Slight : no more than 10 per cent displays a thin covering.
• Moderate : thin covering affecting between 10 and 50 per cent.
• Heavy : heavy deposits affecting more than 50 per cent but with no flaking.
• Serious : heavy deposits displaying surface powdering/ flaking, which increases during wet weather.

Before finalizing sources of brick for procurement, always do sampling of brick and test it for efflorescence as per IS code. If it passes the test, then go for procurement.

Efflorescence can be avoided, or at least minimised, by appropriate design detail and good site practices.

How to Treatment Surface Affected by Efflorescence?

The only real solution to efflorescence is periodically to brush off the salt deposits from dry brickwork as they come to the surface until, over time, all the salts have been released.

Always use a bristle brush and never a wire brush.

It is a mistake to try to wash off the efflorescence as this will merely re-dissolve the salts and wash them back into the brickwork, ready to emerge again when the brickwork dries out.

Do not use acid treatment, as apart from the danger to people and materials by inexpert use, some salts such as vanadium (a trace metallic compound associated mainly with fireclays) may be fixed permanently.

Internal efflorescence may be treated by dissolving small patches with very little water, say a fine mist spray. The surface may then be dried with a damp sponge but, because some users have reported that this sometimes causes a blotchy appearance, it is advisable to experiment on a small inconspicuous surface at first. The absorbent material must be constantly renewed or washed free of salts.

Conclusion

Efflorescence is a common occurrence but can be managed through careful design, construction practices, and periodic maintenance. By understanding the sources and formation process, one can take proactive steps to minimize the impact and preserve the aesthetics and durability of brickwork.