When it comes to the grouting process, one of the most pressing problems in the ceramic tile installation business is getting across the message that there are certain applications that require a flexible caulk joint. A joint filled with cement-based grout will often "open" for a variety of reasons, such as excessive shrinkage or structural movement. This is especially true in newer homes where structural shrinkage occurs and cabinets settle.

If the joint at the juncture between horizontal and vertical surfaces opens, it becomes an area where mold and/or mildew are likely to proliferate. And as most of us are now aware, mold/mildew is one of the latest and hottest litigation specialties.

In most cases, mildew-resistant flexible caulk will prevent such problems. Under "materials" in the Movement Joints section of their 2002 Handbook, the Tile Council of America (TCA) says silicone sealant may be used. The silicone sealant - used for sealing joints in ceramic showers and around tubs, sinks and plumbing fixtures - must be single-component mildew resistant, which means it contains fungicide.

Most of us tend to regard the grout process as a lesser part of the tile-installation job. But when you consider the many problems that frequently crop up relative to this aspect of installation, you will view grouting in a different light.

Causes of cosmetic defects

Discoloration, shading and mottling are probably the most common causes of grout-related complaints. Many contributing factors can be at play in such situations -- so many, in fact, that I'll list the top 10 here.

1. Grouting done on different days or by different crews.

2. Excess bonding mortar squeezed into joint. Proper depth of grout is two-thirds of the tile thickness.

3. Grout not mixed properly -- either not sufficiently mixed, mixed too slowly or mixed too quickly.

4. Over glaze. This occurs when the grout comes into contact with the glaze over the edge of the tile, which alters the drying and hydration time in portions of the grout.

5. Use of cleaners before the grout has set.

6. Use of old grout, particularly when the components of the product have separated within the bag.

7. Mixing water contaminated by chemicals.

8. Excessive cleanup causing water to wash pigment out of the grout.

9. Chemical deposits that migrate from the mortar bed to the grout surface.

10. Inconsistent joint sizes.

I suggest that you may be able to alleviate these problems by dampening the grout joint before grouting, using polymer-modified grouts, damp curing the grout and sealing it.

Other grout woes

Though not as prevalent as grout cracking or discoloration/shading, low, powdery and rough grout are among the other problems that all too often develop in tile installations. Low grout joints are commonly caused by using too much water when washing excess grout from the joint.

Powdery grout joints are frequently caused by poor curing because water evaporates from the grout which, in turn, halts proper hydration. Other culprits include use of cleaning water that contains concentrated acids, and poor mixing with no slake time allowed. Porous and thereby highly absorptive tile can also suck the water out of the grout mix to stop the hydration process.

Rough joints develop when excessively wet sponges pull cement particles away from aggregate. Also, heavy or repeated acid washing will result in rough grout joints.

Efflorescence manifests itself as a crystalline, powdery substance on the surface of the grout or the edge of the tile itself. Efflorescence is composed of salts contained in Portland cement-based material that is brought to the surface by moisture migration. If noticed early, efflorescence may be the result of excess water in the setting bed or in the grout itself. Other possible sources may be uncured concrete slabs and/or contaminated water. This condition may be accelerated by grout that is excessively porous.

Finally, another grout-related problem is latex migration. When this occurs, a rubber-like substance will appear on the grout surface. Where does it come from? Sometimes, it may come from the latex used in a setting bed that wasn't allowed to dry out before grouting was started. Another possibility is too much latex used in the setting-bed mix. Another source may be the use of improper latex that re-emulsifies.