QUESTIONTile Installation over Cracks - I am building a house in Florida, and the slab is a year old, and its cracked. Before I install the ceramic tile, should I use any kind of underlayment to prevent the tile from cracking, and if yes, what kind? Can I use roof paper as an underlayment? I will appreciate your answer, thank you!
ANSWERAnswer - You can not install ceramic tile or stone over cracked concrete without making repairs or providing additional protection or the cracks will continue through the tiles.
If the cracks are structural cracks (they move vertically) then the concrete slab is defective and needs to be properly repaired as determined by a structural engineer.
If the cracks are shrinkage cracks (horizontal movement only) then with some limitations you can isolate those cracks with an appropriate crack isolation membrane meeting ANSI A118.12. You can isolate only the cracks or apply to the whole floor for full projection. Go to our www.CTaSC.com website to Expert Answers and in the Resources column go to Installation Products to get links to manufacturers who provide these products.
You can not use a roofing paper for crack isolation because it doesn't meet the ANSI standards and under certain conditions it is known to fail.