Efflorescence is one type of defect found on plaster surface. Efflorescence is the whitish crystalline substance which appears on the surface of walls due to presence of soluble salts, such as suphates of sodium, calcium and magnesium.
Why Efflorescence Happens on Plaster Surface?
Presence of salts in the lime, cement, sand, bricks and sometimes even in water used in construction work are the cause of efflorescence on plaster surface. After completion of plaster work and when it becomes completely dry; the soluble salts dissolved by moisture are drawn to the surface through pores. These soluble salts absorbs moisture from atmosphere and on drying, they get deposited in patches in form of white crystalline substance. The surface gets disfigured by ugly damp patches of efflorescence. This defect gradually disintegrates the structure. It is normally of temporary in nature as it disappears during wet weather and reappears during dry weather.
How to Rectify Efflorescence or What are the Remedies?
Efflorescent salts cannot be removed by washing with water as it may carry some of the salts back into the pore.
Dry brushing of the growth as it appears on the surface is one of remedies.
The treatment of an old wall with silicon solution will frequently stop the efflorescence as the liquid blocks the passage for movement of moisture.
When efflorescence is due to the rising of salt solutions through capillary action from subsoil; the only remedy is to provide bitumen or metallic seals in the walls above the ground level so that an effective barrier to the capillary action is created.
In case of brickwork, the salt can be removed with a solution of zinc sulphate and water. The surface is brushed off when dry.
How to Prevent Efflorescence in New Building?
Cement gauged lime mortar or moderately hydraulic lime mortar or cement mortar should be used with small proportions of alum and soft soap throughout the work. If possible then use water proof mortar.
The use of damp proof courses should be made wherever necessary.
Only burnt bricks and clean water (free from salts) should be used.
The masonry or plastered works should be well protected at night and during rain to exclude extra water.