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CRACK ISOLATION MEMBRANES
Some of the reasons for cracking include; the substrate has cracked and what you see now is ‘reflective’ cracking coming through the tile; the tile was direct bonded to improperly installed backer board or plywood and the cracks in the tile are directly over the joints in the backer board or plywood.
Are the expansion joints in your neighbor’s driveway visible in the finished tile layer but not in yours? Expansion joints in all substrates should be carried through the finished tile layer. See Tile Council of North America—Handbook EJ171-07 Movement Joint Design Essentials. Under these guidelines: all expansion, contraction, construction, cold, and seismic joints in the structure should continue through the tile work. Exterior Movement joint placement should be 8’ to 12’ in each direction. Expansion and contraction joints should be specified as to location by the architect, builder or design professional.
Without knowing if the cracks are relative to the crack-isolation material used or if these are new cracks, the following areas are possible causes; improperly installed crack-isolation membrane, the thin-set is not bonding to the membrane, new substrate cracks from settling of the house showing up as reflective cracks. What size of tile is installed? With a 12” wide membrane, a tile that is 18”x18” or larger could easily bridge the membrane if it is bonded on either side, effectively canceling any crack isolation properties of the membrane.