Download PDF version (148.2k) Log In or Register to view the full article as a PDF document.
Q.I have been called to inspect a shower with ceramic tile walls. The substrate is cementitious backerboard, and as far as I can tell, the tile was installed with thinset. There are hairline cracks running through the tiles on all three walls, both vertical and horizontal. There is a ceramic soap dish in the corner, and even it is cracked. It doesn’t appear that there has been any movement in the floor or the walls. What could be causing the cracking?

A.Tile expert Michael Byrne responds: Tiles generally crack for only two reasons: loss of bond or moving substrate. In this case, the substrate might be moving if the studs are spaced farther apart than 16 inches on-center, allowing that backerboard to flex.

Another possibility is that the backerboard was cracked prior to installation. Although cementitious backerboard often has minor cracks that don’t cause problems, over-stressing the boards during delivery or installation can cause more serious cracks. If the backerboard was installed over a layer of drywall, then water penetration through tile joints or corners may have soaked and softened the drywall.

If the tiles have parted from the setting bed, they can break when someone applies pressure on the poorly supported tile. A tile can also crack if it is installed over two different substrate materials or an expansion joint. Tiles are strong only when they are cushioned in a bed of adhesive and surrounded by grout.

Solving the problem will require removing the tiles so that the substrate can be inspected.