Though not as popular as grout cracking or discoloration/shading, low, powdery and rough tile 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 flexible grout from the joint.
Powdery grout joints are frequently caused by poor curing because water evaporates from the flexible 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 flexible 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.