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Efflorescence is a common issue in brickwork, manifesting as white deposits on the surface. This phenomenon occurs due to soluble salts present in the materials used for brickmaking and construction. These salts, including those of magnesium, calcium, potassium, and sodium, dissolve in water and migrate to the brickwork surface as the water evaporates, leaving behind visible salt deposits.
Efflorescence in Brickwork
The most common form of efflorescence is a harmless white deposit that often appears on new buildings. While unsightly, it typically does not affect the durability of the brickwork and usually disappears within the first few months of construction, especially if the brickwork is exposed to wet weather.
Sources of Soluble Salts
Efflorescence mainly derives from soluble salts contained in the clay bricks and sands used for mortars. Here are some key sources:
Clay
Clay, the raw material for bricks, often contains various soluble salts. These impurities are impossible to remove before brick manufacturing and can lead to efflorescence and sulfate attacks on cement mortar, especially in walls that remain wet for extended periods.
Mortar Sands
Sands used in mortars typically come from pits or riverbeds, containing minimal salts. However, sea sands, which contain many harmful salts, should be avoided unless thoroughly washed by a reliable supplier.
Cement
Portland cement, a primary binder constituent, contributes minimally to efflorescence. However, modern types of cement with alternative binders to reduce carbon emissions can contain significant quantities of sodium sulfate, a common efflorescence cause.
Detergents Used as Plasticisers
Many detergents contain sodium sulfates and should not be used as substitutes for properly formulated proprietary mortar plasticisers.
Other Sources
Bricks can also absorb salts from ashes, soil, or other materials they contact.
How Efflorescence Forms in Brickwork
Efflorescence forms when water dissolves soluble salts in bricks or mortar, holding them in solution. As the water evaporates, the solution becomes concentrated, and salts are deposited. This can occur within the pores of the brick or on the surface. Predicting efflorescence is challenging due to various factors like the type of salts, pore structure, drying rate, and degree of saturation.
Minimizing the Risk of Efflorescence
While eliminating efflorescence entirely is impractical, its occurrence can be minimized by reducing water penetration in brickwork.
Design Details
Designers can incorporate ‘umbrella’ details to protect brickwork from saturation. Effective roof verges, eaves, copings, and sills can shed runoff water away from brickwork. Avoid designs that shed water onto projecting features.
Site Practice
Bricklayers and site supervisors play a crucial role in minimizing efflorescence through good site practices. Bricks should be stacked off the ground on pallets, mortar materials kept free from contamination, and newly built brickwork protected from saturation, especially during the first week after laying. Scaffold boards adjacent to brickwork should be turned back during rain to avoid splashing and mortar stains.
Choice of Bricks
Manufacturers test new bricks for efflorescence potential, grading them based on the extent of exposed surface area affected:
- Nil: No perceptible efflorescence.
- Slight: Thin covering on not more than 10%.
- Moderate: Thin covering affecting 10-50%.
- Heavy: Heavy deposits on more than 50%, without flaking.
- Serious: Heavy deposits with surface powdering/flaking, increasing in wet weather.
Before finalizing brick procurement, always sample and test bricks for efflorescence according to relevant standards.
Treating Surfaces Affected by Efflorescence
The most effective treatment for efflorescence is periodic brushing off the salt deposits from dry brickwork using a bristle brush. Avoid wire brushes and washing the efflorescence, as this re-dissolves the salts, causing them to reappear. Acid treatment should also be avoided due to the potential hazards and the possibility of fixing some salts permanently.
For internal efflorescence, dissolve small patches with minimal water and dry the surface with a damp sponge. This method should be tested on a small, inconspicuous area first to avoid blotchy appearances.
Conclusion
Efflorescence is a common yet manageable issue in brickwork. Through careful design, construction practices, and periodic maintenance, its impact can be minimized. Understanding the sources and formation processes allows for proactive measures, preserving the aesthetics and durability of brick structures.
For more detailed insights into efflorescence management and construction best practices, explore our other articles. A well-informed approach can significantly enhance the longevity and appearance of your brick structures.
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