Posted by Larry on October 22, 19100 at 22:39:24:
In Reply to: Response to writters comments about efflorescence posted by Evan Lauridsen on October 22, 19100 at 19:58:08:
Very well put, however, I would add that moisture does not nessesarily contribute to tile/mortar bond failure (in regards to slabs with excessive vapor emmissions)- It is the negative hydrostatic pressures that do, which can be reduced by installing a membrane that allows for vapor equalization- hence the Ditra matting suggestion. I don't advocate for permanently "sealing" (meaning any 100% waterproofing product applied to slab whether membrane, sealer, or otherwise) a slab experiencing negative hydrostatic pressures from a tile installation simply because this will most likely cause moisture problems in other areas (e.g. walls) and is no guarantee that the tile/mortar bond will not fail in time as the "seal" is penetrated by the hydrostatic pressure. Of course the proper membrane must be installed to achieve the proper emission/evaporative balance. Humidifiers can also help a great deal by reducing vapor saturation in the air. Proper drainage and run off surrounding the house is very important as well.
Unfortunately, negative hydrostatic pressures are not that uncommon a problem especially in today's varying climate conditions of which tile installers have very little control over. In any case a homeowner with such concerns should most certainly heed Evan's advice and consult with an expert on the matter.