Efflorescence is a common phenomenon observed on the surfaces of concrete and brick masonry structures. It appears as a whitish deposit caused by the movement of water through porous materials, leaving soluble salts behind after evaporation. This article explores the causes of efflorescence, its preventive measures, and the methods to treat and remove it.
Causes of Efflorescence
Efflorescence requires specific conditions to develop. If any of these conditions are absent, efflorescence will not form. The three essential conditions for its occurrence are:
- Presence of Soluble Salts
Soluble salts must be present in the masonry materials, including bricks, mortar, adjacent soil, or backing material. - Water Availability
Water must interact with the soluble salts to dissolve them and transport them through the structure. - Porous Structure
The masonry or concrete must have a pore structure that facilitates the migration of the dissolved salts to the surface, where evaporation deposits them as efflorescence.
Understanding these conditions highlights the importance of material choice, design, and construction in preventing efflorescence.
Efflorescence Treatment on Concrete and Masonry Surfaces
Efflorescence can be treated and prevented through material selection, design and detailing, and good construction practices.
Material Selection
- Use Low-Alkali Cement
High alkali content in cement increases the likelihood of efflorescence. Opt for cement with low alkali content to minimize risk. - Specify Potable Water and Clean Sand
Use only potable water and clean, washed sand for producing mortar or grout mixtures. - Choose Low-Salt Materials
Building trims such as copping, sills, and caps should be made from materials with minimal salt content. - Test Materials for Efflorescence Potential
Conduct tests such as ASTM C 67 to determine whether materials are prone to causing efflorescence.
Design and Detailing
Proper design and detailing play a vital role in preventing water ingress and, consequently, efflorescence formation.
- Watertight Below-Grade Masonry
Groundwater contains soluble salts that can migrate into masonry. Use watertight masonry techniques and install base flashing to redirect water away from the wall. - Flashing on Trim
Flashings should prevent capillary action and ensure no direct contact between masonry and trim materials, which may harbor salts. - Air Space
Incorporating an air space between the exterior wall and the interior masonry reduces efflorescence risk by facilitating drainage and preventing salt migration. - Proper Detailing of Movement Joints
Correctly sized, located, and sealed movement joints limit water penetration, significantly reducing the potential for efflorescence.
Construction Practices
Effective construction practices are essential to minimizing efflorescence.
- Use Clean Water
Construction water should be free of salts to avoid introducing soluble salts into the masonry. - Protect Materials
Prevent contamination of masonry units by storing them away from dirt, groundwater, rain, and snow. Ensure they are covered during transportation and construction. - Ensure Proper Joint Filling
Fully filled mortar joints prevent water ingress. This applies to solid unit masonry as well as hollow unit masonry. - Cover Unfinished Brickwork
Use waterproofing membranes to protect incomplete masonry work from rainwater and saturation, which can prolong drying times and increase the risk of efflorescence.
Removal of Efflorescence
Efflorescence removal depends on the type of salt and the extent of the affected area. Common removal methods include:
- Dry Brushing
Effective for soluble salts, this method uses a brush to remove deposits without water. - Rinsing with Water or Other Liquids
Water can be used to wash away efflorescence, especially for larger areas. - Hand Washing
Suitable for small patches, this involves scrubbing the affected area with appropriate cleaning tools. - Sandblasting
For stubborn deposits, sandblasting can be used, although care must be taken to avoid surface damage. - Special Chemical Cleaners
These cleaners are designed to dissolve and remove efflorescence effectively. - Ordinary Chemical Cleaners
Common solutions like muriatic acid may also be used, but proper safety precautions are essential.
It is important to note that cleaning efflorescence does not resolve its root cause. Preventive measures such as sealing the wall are necessary to address the underlying issue and avoid recurrence.
Conclusion
Efflorescence is a result of specific conditions involving soluble salts, water, and porous materials. Prevention starts with selecting appropriate materials, employing good design practices, and following proper construction methods. While several methods exist for removing efflorescence, long-term solutions require addressing the root causes. By adopting preventive measures and proactive maintenance, efflorescence can be effectively managed in concrete and brick masonry structures.