Keep Heavy Tile on the Ceiling
When installing tile overhead, make sure the substrate is solid and stiff, and that it provides a good bond.
Q:
I’d like to extend marble wall tiles up to and across the ceiling of a walk-in shower. I plan to apply a Kerdi decoupling membrane over 1/2-in. mold-resistant drywall.
What do I need to know about installing marble tile on a ceiling? Should I use thinset, or would mastic be the better choice? Should I tighten up the joist spacing?
Justin Fink, Glastonbury, CT
A:
Tom Meehan, owner of Cape Cod Tile Works in West Harwich, Mass., replies: Many years ago, a piece of limestone tile fell from a ceiling onto my head two days before I appeared on a panel at a trade show with fellow tile expert Michael Byrne. I ended up with nine stitches in my forehead and two black eyes. Michael then ribbed me at subsequent shows, saying, “I didn’t recognize you without the black eyes.”
Since that incident, I have used cementboard as a tilebacking substrate because it provides a tenacious bond. It is a great idea to stiffen the ceiling framing before the cementboard is installed because if the ceiling can flex, a tile could fall.
I wouldn’t use membrane on the ceiling. Tile should be bonded directly to the cementboard with a good latex-modified thinset cement (definitely not mastic) such as TEC Super Flex (www.tecspecialty.com), Laticrete 333 (www.laticrete.com), or Mapei Ultraflex 2 (www.mapei.us). Mix the thinset with a mixer rather than by hand, let it slake for five minutes, and then mix it again.
If the thinset is mixed perfectly well and has good tack to it, the marble tiles will stay in place, but never trust a ceiling-tile bond until the next day. Don’t turn your back on the pieces or work under the pieces that you’ve installed. For large ceilings, I usually do half of the ceiling at a time and work my way out the door. The next day, when the tiles are set, I do the rest of the ceiling.
