STAINING TO CONCRETE BALCONIES AND STAIRS
White efflorescence is a staining, discolouration or film that becomes evident to external areas at or near tiled surfaces.
This is a result of mineral salts and crystal formations leaching out from the sand and cement bed below balcony or stair tiles. Water (usually rainwater) migrates onto the tiles and is absorbed into the bed below the tiles via the grout joints.
The sand and cement bed becomes saturated with moisture and dissolves the salts and crystals which then migrate to the outer or lower surfaces. At the egress point it leaves the efflorescence on the surface of the tiles or walls. The efflorescence is a hardened film or mineral salts and crystal or calcium formations.
Efflorescence can occur to the underside of concrete slabs where fine shrinkage cracks become evident. On some occasions the film may be evident to grout joints in a bathroom, mainly within the shower.
Efflorescence usually occurs where a sand and cement bed is placed below a tiled surface. The reason is the type of cements currently being used in those tile beds. The current cements are a slightly different type to several years ago and contain some ash. Where tradespeople use traditional methods for installing a sand and cement bed, then efflorescence will become evident. Additionally the sands may contain some impurities. In Sydney, some sand is being dredged from below sea level and contain additional salts. Efflorescence formations have a limited life as when all the salts and crystals have been saturated out of the sand and cement bed, then it will be exhausted and not be a future issue.
The requirements for good practices is varied and many and will depend on the requirements of each individual job. One option is to use cement that does not contain ash. In essence, there must be some provision to allow the efflorescence to dissipate without affecting adjoining areas or use a method where moisture does not enter into the sand and cement bed. Also, where external balconies have a brick handrail, there must be adequate provision in the waterproof membrane for movement between the concrete patio slab and the base of the brick wall.
Where efflorescence is evident, then it requires removal by various means. In very light situations, it can be removed with a scraper or hosed off on a regular basis. Where larger formations are evident, removal is best referred to a cleaning contractor. That may include using diluted acids to soften the formations. Using of acids is not recommended without some knowledge of the hazards of that product and the suitability on various tiles and reactions of those tiles to acid.
Contact can be made to our office where experts can assist in methods to reduce this issue.