A.Contributing editor Michael Byrne, a tile-setter and consultant in Los Olivos, Calif., and moderator of JLC Online's tile forum, responds: The quality and density of slate can vary quite a bit. Honed slate tiles dense enough to be exposed to water don't absorb sealers readily, whereas some softer slates with cleft finishes will actually start disintegrating in water.

And while not all penetrating sealers perform well with slate, top-coating sealers can lead to disaster when they yellow and begin to chip off.

Generally speaking, I think that most tiles made from porous stones like slate and limestone are a bad choice in a shower stall. Regardless of the type of sealer used or how often it's applied, keeping slate or limestone in a sanitary condition is almost impossible, as is removing the "dirty clothes" smell that these stones tend to accumulate.

Porcelain-tile look-alikes might appear to be the first and best alternative, but they have their problems too. Some of these tiles have a coarse texture meant to make them slip-resistant; unfortunately, it also allows dirt, grime, grease, soap, and oils to lodge permanently on the tiles' surface.

For best results, choose a smooth-surface stone tile with absorption properties similar to those of vitreous or impervious tiles — and avoid any stones that require topical applications to achieve these desired properties.