Honoring expansion joints in a concrete floor is critical to the success of a ceramic tile floor installation. Choosing to ignore them is a bad idea and will eventually come back to haunt the installer for a long time. Actually, they don’t go away; they just get worse.
First, let’s define an expansion joint. The American National Standards Institute (ANSI) A108.01 section 3.7 provides this explanation: “Expansion Joint: (1) A separation provided between adjoining parts of a structure to allow movement where expansion is likely to exceed contraction; (2) a separation between pavement slabs-on-grade, filled with a compressible filler material; (3) an isolation joint intended to allow independent movement between adjoining parts.”
ANSI A108.01 section 18.104.22.168 states, “Openings for movement joints shall extend completely and directly through tilework down to structural backing.” This sentence means that when tile is installed on a concrete floor which contains expansion joints, a sealant joint (aka caulking joint) must be placed in the tile installation immediately above the joint in the concrete.
The Tile Council of North America (TCNA) Handbook goes on to state, “Joints through tilework directly over structural joints must never be narrower than the structural joint.” This means that if the expansion joint in the concrete is 3/8" wide, the sealant joint in the tile must be the same size.
Now the problem. Unfortunately, some installers ignore the presence of expansion joints in the concrete floor by filling the space with thin set mortar and installing tile over the joint. At this point the installation looks good and the installer gets paid. The problem comes when the building moves from temperature and/or humidity changes. When the slab expands or contacts, that movement has nowhere to go except up through the tile. The resulting crack generates a callback which requires the installer to go back and repair the cracked tile at his or her expense—hoping there is matching tile to complete the repair.
The attached photo is a prime example of a 24" x 24" tile being installed over the expansion joint in the concrete. If you look closely, you will see that the cracks in the tile occur very closely to the grout joints. If the installer had shifted the north/south tile layout just 6" to the left and moved the east/west tile layout 2" north, the grout joints would have been in alignment with the concrete joint and this eyesore would not have occurred.
If you follow these guidelines, customer problems will not be on your voicemail.