Efflorescence is a problem associated not only with ceramic tile and grout installations but also with vinyl composition floor tile (VCT). For those who need a quick explanation, efflorescence consists of soluble salts (alkali) that are brought to the surface of concrete whenever moisture is present, either from a source above or below the slab.
In the case of resilient tile, the effects of alkalinity exposure can be particularly harmful. Typically, the alkaline salts will attack the edges of the tile and, in effect, cause the tile to lose its "flexibility" at the points of exposure and become hard and brittle. If present continuously, alkaline salts will also attack organic bonding adhesives.
Efflorescence that appears on ceramic tile grout joints and, in some cases, on porous clay tile may be the result of: 1. Over-mixing of grout, which increases its porosity and allows moisture to travel upwards. 2. Green, uncured slabs (practically all salts come from the slab). 3. Too much water in the setting material. 4. Water vapor/moisture emanating from a slab in the absence of a vapor barrier. 5. Use of calcium chloride in concrete to accelerate its set (a technique used especially in cold climates). This increases porosity and allows moisture to travel upwards to the surface.
Efflorescence may be removed by cleaning the concrete surface with sulphamic acid or other special cleaners manufactured for this purpose. When acid or other cleaners are used, the slab subsequently should be washed with clean water. If the moisture situation is not serious, and moisture has left the slab on its own, the efflorescence may just vanish over time.
It's important not to confuse latex migration with efflorescence. Latex film that results from migration will be somewhat flexible or rubbery. Latex migration in the grout may be caused by adding too much latex additive to the grout and/or mortar. Another reason for migration may be due to the presence of moisture that prevents the latex in the grout from solidifying which, in turn, allows it to migrate to the surface.
While I'm addressing efflorescence and how it affects the grout line, I might as well discuss another grout problem -- "mottled" grout that has an inconsistent color. One primary reason for color inconsistency is excessive overglaze on the tile which prevents even curing of the grout.
On the other hand, where there is no glaze, the tile body is absorbent. As a result, the tile itself sucks water and pigment from the grout and causes it to dry unevenly. Allowing grout to dry out too fast affects its color. Damp curing will help prevent this problem.
Poor or improper mixing procedures will definitely cause mottling in the grout. Additionally, excessive cleanup water can wash out pigment. When different installation crews work on separate walls on the same jobsite, claims of grout color inconsistency are not all that uncommon.
An even more serious problem in the installation of ceramic tile and stone stems from an inadequate understanding of the requirements for a good thinset installation. Most failed installations are caused by dusty or contaminated concrete, dusty tile backs, too small of a mortar bead (trowel should be held at a 45-degree angle), skinned-over mortar, and badly mixed mortar. Such conditions lead to poor transfer of the thinset to the tile back.
To avoid job callbacks, be sure to review the basics. First, consider the substrate. If curing compound was used on the slab, check to ensure that it has been removed. Is the substrate contaminated by drywall gypsum dust or does it have paint overspray on the surface? Either situation should be remedied before proceeding with the installation. Be sure that adequate attention is paid to the mortar-mixing process -- it should not be overmixed and water should not be added after mixing is complete. Always allow the mortar to slake.
Once the proper substrate requirements have been satisfied, make certain that the proper-sized trowel is used. Don’t stretch out the mortar, and maintain a 45-degree trowel angle throughout the application. Don't wear out the trowel notches.
After those concerns are addressed, make sure that adequate transfer of the mortar is being achieved. Improper transfer can be caused by skin-over on hot days or by spreading the material too far ahead of the tile placement.
Transfer is especially critical when installing the new larger-format tiles that cannot be effectively "beat in" to the mortar bed. In such instances, a new spreading pattern developed by the National Tile Contractors Association (NTCA) might be worth considering. To obtain more information, telephone NTCA at (601) 939-2071 or visit www.tile-assn.com on the Internet.