QUESTIONCracks in Concrete Slab - I plan on having 18" porcelain tile installed in my home over a concrete slab foundation. There are miner cracks in the foundation. I was told that the cracks will not cause my tile to crack because my house is 17 years old, and therefore, is through setteling. What is your opinion?
ANSWERANSWER - Per our industry standards for ceramic tile and stone and from a practical point-of-view, any concrete substrate that has shrinkage cracks should be isolated with a crack isolation membrane.
If the cracks are structural cracks where there is a height difference from one side of the crack to the other then the crack isolation membrane will not provide protection and the crack will have be repaired with epoxy and dowel pins.
Shrinkage cracks will continually move in a horizontal plane and need isolating so they will not continue up through the tile.
Be sure to adequately place movement joints (expansion/soft joints) throughout the tile floor and along the perimeter where it abuts restraining walls. They should be placed every 20' to 25' each direction interior and for exterior or near interior windows and skylights every 8' to 12' in each direction. Use a proper sealant meeting ASTM C920 i.e. 100% silicone, urethane or polysulfide (not a latex caulking).
For website links to manufacturers of installation systems to go our website Resources and Links section under installation products