Efflorescence in concrete simply means apperance of white colored powder material on the concrete surface . Efflorescence is the formation of salt deposites, usually white on a near the surface of concrete after it has been finished and causing a change in apperance.
Light colored concrete shows the deposite much less than darker colored concrete.
The alkaline salt present in the brick obserb moisture from air which on drying leaves powder deposite on the brick It is also caused if pyrite was present in clay used for brick making and water used for pugging contains gypsum.
Effects of Efflorescence :
Effects of Efflorescence in dampwall leading to various damages like unhygenic condition, decay, dry of wood, disintegration of masonry damage to furniture and internal de-coloration …..etc.
Causes of Efflorescence:
- 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 source of water .
- Slow rate of evaporation of water allowing time for salt to permeate to the surface.
- Variability of concrete can result in localized problems where water can permeate more easily through the concrete.
Preventive of Efflorescence in concrete
1.Use ingredients containing as tittle soluble salt as possible
2. Use water proofing 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 masonary ensure flashing, damp proof course are detailed correctly, cover the top course at the end of each day work.
Eradication of efflorescence
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 slury 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 water proofing admixture.
- If causes is due to 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 new one.
It can also be done by following;
Brushing soluble salts deposites can be removed with a stiff bristle broom. Note that all brushed of materials should be totally removed by vaccum cleaner or other means. If the result is not satisfying , scrub with clean water then lightly rinse the surface. Note that adding water may result in further deposite, repeated dry brushing as the deposite appears is probably the best treatment. Insoluble salt deposites cannot be removed by water washing although the use of high pressure water jet is effective.
b. Using dilate acid solution
The application of a dil. acid solution is also very effective in most cases and in some cases may be the only way. extreme care is required while handeling acids. when diluting HCL acid, always add the acid to the water never the reverse.
Ensure good ventilation and also avoid the contact between the acid and the reinforcement. Concrete surface should be cleaned with only diluted acid.
The recommended proportions are 1 part HCL and 20 parts of water. Surface should be saturated always before the application of dilute acid. when applying the acid solution ensure that the surface is surfacely moist but without any free water being present. Then applied solution should be allowed to react on the concrete surface for 10-15 minutes. The surface should be throughly rinsed and scrubbed with lots of clean water. Repeat rinsing at least twice or until a all traces of the acid solution have been removed. The process may be repeated if required to bring necessary surface finishing.