Q: 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 the marble tile flooring is installed so that it doesn't crack? Also, is cleaning marble tile an issue?
A: Your marble tile bathroom is going to look splendid, and with minimal care and effort it will look gorgeous for many years.
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 when compared with granite or porcelain tile, but it is fairly durable. Some marbles are as hard as granite, so look for those for 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 out of the box. In fact, I just installed marble floor tiles that had a tendency to crack along the coloration veins. A few tiles in each box seemed to do this, so I had to be careful about how each tile was handled.
Marble is like any 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 under the marble tiles must be solid and have little or no bounce or flex in it. Seasonal changes in humidity also can cause cracks as the floor picks up moisture and swells. Make sure you install the marble tile on top of a crack-isolation membrane.
It's also very important for the subfloor to have no bumps or dips. Use a self-leveling underlayment compound that pours onto the floor like runny pancake batter. The material spreads out and levels itself, making the floor all in the same plane. 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 the cement-based thinset mortar, there's no issue.
Before you start the job, talk with your wife about the orientation of the tile in the room. The easy way to install marble tile is with the side of each tile parallel with a wall in the room. Installing the tile diagonally, however, can make for an interesting look. This means the tiles are set at a 45-degree angle to the walls. This method is harder to install when it comes to cutting each tile, but the final look is stunning.
I've had the best luck using a 1/8-inch gap between each tile. I maintain this spacing using circular plastic spacers. These spacers are shaped in such a way that one side is used where four tiles intersect and the other side can be used to create the gap at any point along the edge of a tile. They also are reusable, as they sit on top of the marble tile.
If you don't exceed a gap of 1/8 inch between each tile, you can use unsanded grout between the marble tiles. I like this look, and the lack of silica sand in the grout ensures that the highly polished surface of the marble won't get scratched as you spread the grout on top. To prevent shrinkage cracks in the grout, be sure it's mixed with minimal water. The grout should be of a consistency that it will not sag if you tilt the bucket on its side.
Tim Carter is a licensed contractor. To view previous columns or tap into his archive of information and sources of building materials, go to www.askthebuilder.com. You can write to Tim Carter at P.O. Box 36352, Cincinnati, OH 45236-0352.