What do you think of this reason from Bal? I would have thought that the three conditions are present in all grouting situations:
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Dear Iain, Thank you for your correspondence via our website. The problem that you are encountering sounds very much like efflorescence. Efflorescence is a crystalline or powdery deposit (normally white in colour) which forms on the surface of cementitious products. These deposits are chemical compounds which form when water soluble salts form on the surface, normally carbonates, sulphates or chlorides of calcium, sodium and potassium. In Portland cements, the most common form being calcium carbonate. The presence of efflorescence is well documented in The British Standard Code of practice BS 5385 Part 3 1989 and is mentioned in 16.2 Passage from below and also in Section 7. Cleaning and maintenance For salts to form there must be the presence of the three following elements.- <LI class=MsoNormal style="TEXT-ALIGN: justify; mso-list: l2 level1 lfo1">soluble salts present in the substrate. <LI class=MsoNormal style="TEXT-ALIGN: justify; mso-list: l2 level1 lfo1">water must be present.
- evaporation or hydrostatic pressure, or other force to cause the water and minerals to the surface.
To prevent efflorescence from forming you need to eliminate one of the above elements. Therefore ensure that where possible: -a suitable vapour barrier is positioned on the sub-floor in the form of a surface DPM (damp proof membrane) which is compatible with the adhesive -there is no excessive water being added to the grout which will cause the migration of natural salts within the cement to the grout surface -there is no moisture trapped within cavities or the sub-floor allowing salts to migrate from the background -the drying time of the grout joints is not extended by covering with polythene or similar material. Efflorescence can normally be removed by washing down with clean potable water. This may need to be repeated where the deposits are light to medium. Where the salt deposits are heavy they may be removed by the application of a suitable cleaner. For limestone we would NOT recommend the use of an acid based cleaner as this may react adversely with the limestone. We would recommend the use of a NEUTRAL cleaner but would strongly advise you to check with the manufacturer prior to use to confirm suitability. Apply using a stiff bristle brush or emulsifying pad. ·On large areas use a rotary cleaner. ·Leave on the surface for between 5-10 minutes. ·Work cleaner in to grout surface again. ·Mop up residues. ·Wash off with clean potable water. ·Repeat where necessary. For further advice please contact the Stone Federation Great Britain on 01303 856123. Hope you find this of use.