Q: DEAR TIM: My wife insists on marble tile in our bathroom. I've never worked with it and wonder about how smart a choice it is. Is marble floor tile durable? What should I know to ensure it doesn't crack? Also, is cleaning marble tile an issue? -- Steve P., Florence, Ky.



A: DEAR STEVE: Your marble tile bathroom is going to look splendid, and with minimal care and effort it will look gorgeous for many years. And, best of all, your wife will be smiling ear to ear.



Marble is a natural stone formed when limestone is heated and subjected to intense pressure. The crystals in the rock reorganize, often creating a denser rock with interesting coloration and veining.



Marble can be softer than granite or porcelain tile, but it's fairly durable. Some marbles are as hard as granite, so look for those if you want the most durable flooring. Sand and acidic liquids are marble tile's biggest enemies. If you can keep these things out of the bathroom, you'll be able to keep the marble sparkling for years.



Some marble tile is fragile. In fact, I just installed marble floor tiles that had a tendency to crack along the coloration veins. Marble is like ceramic tile or natural stone when it comes to cracking. These materials all have impressive compressive strength -- meaning they don't fail if you squeeze them. But if you bend or stretch marble, it can crack easily.



This means the subfloor must be solid and have little or no bounce or flex. In the case of a wood subfloor, you don't want seasonal changes in humidity to cause cracks as the floor picks up moisture and swells. Install the marble tile on top of a crack-isolation membrane.



The subfloor also must be in the same plane, with no bumps or dips. Use a self-leveling underlayment compound that pours onto the floor like runny pancake batter. Just about all of these materials are rated to be used under marble tile.



Cement-based thinset mortar bonds the marble to the subfloor permanently and prevents the marble from separating. Once the polished marble tile is set firmly in thinset, there's no reason to worry about cracking.



Before you start the job, talk with your wife about the orientation of the marble tile in the room. The easy way to install marble tile is with the side of each tile parallel with a wall. But installing it diagonally makes the floor really look interesting. This means the tiles are set at a 45-degree angle to all the walls. This method is much harder when it comes to cutting each tile, but the final look is stunning.



I've had the best luck using a one-eighth-inch gap between each tile. I maintain this spacing using circular plastic spacers. These spacers are shaped so that one side is used where four tiles intersect and the other side can be used to create the exact gap at any point along the edge of a tile. They are reusable, as they sit on top of the marble tile. Spacers that drop down in the gap between tile can interfere with the thinset mortar, causing a mess.



If you don't exceed a gap of one-eighth of an inch between each tile, you can use unsanded grout. I like that look, and the lack of silica sand ensures that the highly polished surface of the marble won't get scratched as you spread the grout. To prevent shrinkage cracks in the grout, be sure it's mixed with minimal water. The grout should be the consistency of cool cake icing that will not sag if you tilt the bucket on its side.