Efflorescence in concrete simply means the appearance of white coloured powder material on the concrete surface. Efflorescence is the formation of salt deposits, usually white on a near the surface of the concrete after it has been finished and causing a change in appearance. Causes of Efflorescence may be differents like high water-cement ratio, containing of salt, etc.
The alkaline salt present in the brick absorbs moisture from the air which on drying leaves powder deposited on the brick It is also caused if pyrite was present in clay used for brick making and water used for pugging contains gypsum.
- One or many constituents of concrete may contain salt
- High water-cement ratio resulting in a more porous concrete that allows movement of outer and salt solution.
- In-adequate curing which may leave un-hydrated products near the surface of the concrete.
- Exposure to rain or other sources of water.
- The slow rate of evaporation of water allowing time for the salt to permeate to the surface.
- Variability of concrete can result in localized problems where water can permeate more easily through the concrete.
1.Use ingredients containing as tittle soluble salt as possible
2. Use waterproofing admixtures to reduce the permeability of concrete
3. Use denser concrete to reduce permeability
4. Avoid premature drying
5. Use cement, lime and mortars no stronger than required for the application to minimize possible soluble salt level . lime should be hydrated & lime-free from calcium sulphate.
6. For masonry ensure flashing, damp proof course are detailed correctly, cover the top course at the end of each day work.
For the eradication of efflorescence problem the source of ingress of moisture should be determined first, the cause of ingress may be due to defective DPC or absence of DPC or other causes.
- The first action is to stop the source of ingress of moisture.
- The second step should be to remove plaster from both inside and outside and leave it to dry.
- Then removing the defective bad brick or filling voids with mortar then by cement slurry or cement concrete.
- Check the mortar joint carefully and removing loose mortar where necessary.
- Wash the white patches surface with the acidic water and then wash it again with clean water.
- Plaster both inside and outer surface with cement mortar adding waterproofing admixture.
- If causes are due to the absence of DPC course or due to failure of DPC; new course of DPC should have to be introduced or replace the defective DPC by the new one.