QUESTION

How to install tile on a Ceiling? - I am working on a small project, and we wish to install a 16" x 24"x 3/4" tile, to a cement ceiling. Are the mechanical fasteners (hopefully concealed) for this application, or is there an epoxy / mortat / thinset that will safely work for this type of inverted installation?

ANSWER

ANSWER - With a large format tile like that you can adhere it to the ceiling without a mechanical attachment unless your local codes require a mechanical attachment. The International Building Code (IBC) allows for adhering stone that weights 15 lbs per sq. foot or less. Chances are your tile doesn't weight more than that, but you need to verify.

Using a high quality polymer modified thin-set mortar will provide a shear bond strength of 500 psi or more as long as you prepare the structurally sound substrate properly and install it properly it. So a 16x24 inch tile is 384 sq. inches times 500 psi equals 192,000 pounds of force theoretically. Actually when shear tested in the field a well bonded tile will achieve about 100 to 200 psi shear bond strength before it fails, and it typically fails cohesively within the substrate to which it is attached. e.g. plaster brown coat or concrete wall. But still at 100 psi that is 38,400 pounds of holding force.

Typically on large format tiles if you use a good thin-set that is mixed correctly the tile will hold itself in place on a ceiling, due to the suction that is created, as it cures. You might need to use spacers and tape two adjacent tile edges together to make sure it doesn't move.

If you want the added assurance that it is attached well, you can counter sink screws into the stone. Use a small diameter hole saw to drill a hole partially through the tile, and keep that plug for reinstalling with thin-set after you screw the tile in place.

Make sure you key the thin-set into the clean substrate and the clean back of the tile with the flat side of the trowel, and while it is still tacky apply enough thin-set to achieve substantially 100% thin-set contact.