Not what it’s cracked up to be?

Question: I had 12-by-12 ceramic tile pavers installed on my kitchen floor. A short while after, a crack several feet long appeared in the grout. Other cracks have appeared. The contractor said the floor was flexing, but it seems solid to me. He said that the only solution was to install a supporting beam below the floor to minimize flexing and therefore the cracking. This seems to me to be an extreme measure. Why are the cracks appearing, and what can be done?

Answer: An experienced contractor who works with ceramic tile should be well aware that a substantial substrate is needed to prevent grout cracking when tile is installed over a wood-frame floor.

In new construction when tile is used over a wood-frame floor, the strength of the floor in that area is increased, and that floor is usually built about 2 inches lower than the floors that don’t get tile or stone. This makes room for a 2-inch-thick layer of mortar and steel rods that adds rigidity and strength. In remodeling, the floor is reinforced from below with extra piers and/or additional floor framing members. It is wise to add a 1-inch-thick layer of mortar below the tile for even more strength; this is expensive and usually creates a change in floor levels.

Without seeing your floor, it is difficult to determine whether it is flexing or shifting laterally because both can cause the condition you describe. If your contractor is right, extra supports under the house will reduce flexing. However, if your house is shifting laterally other measures may need to be taken.

It might be cheaper to assume that the contractor is right and add the supports. If the condition persists once supports have been installed, contact a soils engineer.

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