Efflorescence or “lime bloom” is a general term used in the construction industry, to describe the white deposits that can be found on any good quality cementitious product. The term efflorescence covers several different phenomena, and different forms of efflorescence can occur on products as a result.
The duration of efflorescence on such cementitious product is dependent upon the quality and type of the deposit and upon prevailing conditions. Water/moisture which is initially responsible for its appearance is also largely responsible for its disappearance. Rainwater carrying dissolved acids from the air not only dissolve the chalk-like deposits, but also mechanically removes it as it flows down the roof slope. The process may be assisted by warm dry weather when the deposit is blown away. Although it is impossible to state exactly how long efflorescence will take to be removed by the weather, a period of suitably adverse conditions, especially frost, is usually sufficient to restore the product to its expected appearance.
Efflorescence may sound like a complicated chemical phenomenon, but in reality, it is merely a superficial characteristic feature of good quality product, which is gradually removed by the process of natural weathering.
The following questions and answers hopefully address the key issues concerning efflorescence.
Q. Why has it happened?
A. Efflorescence, when it occurs, is a natural phenomenon brought about as a result of the normal reaction between cement and water. A product of this reaction is a calcium hydroxide “lime”, which is slightly soluble in water. Under certain conditions it can migrate to the surface where it in turn reacts with carbon dioxide in the atmosphere to produce calcium carbonate crystals, most commonly taking the form of white “stand up” chalk –like deposits or streak marks.
Q. How does it occur?
A. The occurrence of lime bloom or efflorescence on cementitious products is spasmodic and unpredictable, but a significant factor seems to be the weather conditions
Efflorescence forms more readily when the product becomes wet and dries slowly and therefore there are more occurrences during damp periods. It is also generally only likely to occur in the early life of applicable products and materials installed for a year of more without experiencing lime bloom, are unlikely to be affected in the future.
Dampness within any new building, due to new concrete flooring groundwork or certain seasonal weather activities, may also add to the efflorescence effect and can all allow excessive moisture to be retained within Fibre Cement Profiled sheeting.
Q How long will it last?
AIt is also difficult to ascertain how long the effects last and this depends upon the amount of deposit and local weather and atmospheric conditions. The action of wind and rain gradually removes the deposits, leaving the intended colour of the chosen product without further efflorescence occurring. As rainwater is slightly acidic, it dissolves the deposits on the product surface and the deposits will normally be expected to disappear within 12 months but this is not always the case. As it is only superficial, the strength and durability of the product is unaffected.