What can be done about efflorescence?
A major reason for using tiles is that, when installed properly, tiling looks very attractive. Almost any tiling project though, risks being blighted by efflorescence. This term covers a wide variety of chemical compositions which can precipitate onto the surface of tiles, mortars and grouts. It typically takes the form of a whitish deposit on the surface of grout lines, most frequently in flooring applications. Efflorescence will often appear as a white stain on coloured floor grout during the setting or drying out period, to create light and dark ‘patchy’ joints.
Efflorescence does not cause actual damage beyond the aesthetic impact. The amount that occurs is related to factors including the amount of water and available soluble salts, normally calcium, and drying times. The longer that moisture is present, the greater the chance of salts dissolving into it, before permeating to the surface during drying. Efflorescence is usually encountered in newer constructions and is more likely to appear during colder weather as well as being particularly prevalent when grey Portland cement is used.
For efflorescence to occur, there must be soluble salts in the substrate or cement, water must be present and either evaporation or hydrostatic pressure must be present to bring the water and minerals to the surface. The likelihood of efflorescence can be exacerbated by adding too much water to the grout during mixing or by over-washing the grout joints during the cleaning off process. Cool weather is also a problem: the colder the air temperature, the colder the backgrounds and bases. For any construction material containing cement, the rate of cement hydration and the rate at which residual moisture is lost slows as ambient temperature falls, particularly at temperatures below 10° C. The relevant British Standard, BS5385-4, recommends not tiling below 5° C.
Preventing efflorescence from forming requires the elimination of as much as possible any of the three constituent elements. With floors, it means ensuring that where necessary a suitable vapour barrier is positioned on the sub-floor, in the form of a surface damp proof membrane which is compatible with the adhesive. There should be no moisture trapped within cavities or the sub-floor allowing salts to migrate from the background. Avoid extending the drying time of the grout joints caused by covering with polythene or similar material and be certain that excessive water is not added to the grout.
If, despite all precautions, efflorescence does occur, it can be removed. This is normally possible by washing down with clean water, although the process may need to be repeated where the deposits are light to medium. For heavier salt deposits, a proprietary cleaner will be required.
For limestone, marble tiles, concrete stone, terrazzo or any hard stone with is not acid-resistant, a non-acidic cleaner such as Aquamix Eff-Ex or an equivalent Lithofin product will be required. With other tile materials, efflorescence may be removed by an acid-based cleaner such as Lithofin Builders Clean. The surface should be pre-wet before application of the cleaner which can be diluted at up to 10:1, according to circumstances. After application with a stiff brush, it is left for up to 10 minutes (but not allowed to dry), worked into the surface again, then rinsed off with clean water. Alternatively there are grouts available that are formulated to reduce the risk of efflorescence forming such as BAL Microcolour.
Removing efflorescence should be straightforward, providing that the right type of cleaner is used for the materials involved. As is usually the case, however, prevention is better than cure and certainly requires less time, effort and investment.
For free impartial advice on any aspect of tiling, BAL’s experts are readily available during working hours on 0845 600 1222.
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