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Tile in thin-set is loose

Topic: 
Flooring - Tile
Question: 

Last year we installed ceramic tiles in our sunroom. within a few months the grout was cracking in a few locations. After further examination the tiles were loose were the grout was cracking. we removed the loose tiles wiht little effort and noticed the thinset was stuck to the subfloor and not the tile. The thin set can be removed from the subfloor with little effort.The contractor never experienced anything like this in the past.

He thought the floor was moving and recommended to add additional joist supports before we attempted to remove and reset the tiles, which I did.( I sistered the joists with 2x8,s )I also added additional ventalation to the enclosures under the sunpoarch. ( 6inch vents every 3 ft.)Also, the tiles that are stuck can be removed using a wood chisel under them with a slight tap with a hammer without damaging the tile. Again very litte or no thinset sticking to the tile.

The structure is 2x8 joists ( now doubled) 2x 6 flooring nailed to the joists and 3/4 in plywood subfloor screwed every 3 to 6 inches. The sunroom is on the south west corner of the house.

Answer: 

James,

Without a great deal more information I am unable to tell you the exact cause of your tile problem. But I can provide you with some information that should help you solve this problem:

  • Plywood is a poor substrate for tile, especially tile in the sun room or in wet locations. The tile should be set on a concrete board or similar material.
  • The floor structure must meet standard framing practices and as a general rule, 2x8s are not used as floor joists. I don?t know your spans at this location but most floor joists are 2x10s.
  • Freeze-thaw cycles can damage porous tile and may also brake the bond between tile, thin-set and plywood.
  • In order to create a good bond between materials, all of the surfaces must be clean and dry. Bonding re-used material is very difficult.

      In short, thin set works very well when all of the surfaces are installed in a workmanlike manner and manufacturers? specifications.

      George