QUESTIONCeramic Tile hollow, loose and grout cracking: we're having problems on a newly layed ceramic tile floor (kitchen) developing grout line cracks and upon investigating, are finding that the thinset w/latex is mostly bonded to the tile but not always to the plywood beneath. All of the materials used and the structural components are acceptible (2x10 fir joists on 16" centers with additional bracing set on a new block foundation with a total of 1 1/4" of exterior grade plywood flooring screwed on 6" centers throughout) and the cracks have all developed in the areas we walk or stand the most (in front of stove etc). We've taken a rubber mallet all over the floor and can hear a hollow sound beneath the tiles adjacent to the cracks, but also under 2 other tiles where we've never put weight on. The other fact is that the mudroom was also done at the same time with the same materials, but it seems fine. the tile was layed on one day (ending about 3pm)and our installer said it would be fine to walk on the following morning (7ish). We followed his instructions, but had no reason to go in the mudroom for many more hours. The temp. in our house is between 60 and 65 at night - is it reasonable to think the thinset was bonded by the morning or might we have dislodged it at 16 hrs.. or is it a bad batch of thin set...or should we be looking else wear. thank you for your expertise!
ANSWERANSWER - When there is ceramic tile or stone failures it is normally due to compounding issues.
There could be excessive movement beyond the industry limit of L/360 deflection, but your subfloor description sounds substantial.
There are supposed to be properly designed and installed movement joints/expansion joints at the perimeters, all transitions, and within every 20' to 25' in the field for interior applications. The lack of movement joints could be a contributing factor.
Sounds like you bonded the tile direct to a wood substrate. This isn't the best method of installation, but if done correctly will meet industry standards. There should be gaps between the sheets of plywood and they should be placed off-set from each other and the underlying subfloor. A special EGP modified thin-set meeting ANSI A118.11 should have been used to bond to the wood. There can be no contaminates on the wood surface. If the tile was a porcelain or very dense tile then it would take longer to cure particular at the lower temperatures you mentioned.
If thin-set bonds well to one material and not the other then it would not suggest the thin-set is faulty. There are many reasons why the thin-set did not bond or stay bonded to the wood surface. To fully understand your situation would require a forensic investigation. Of course there is a cost to that depending on how far you want to take, but an investigation with a formal written report normally runs $2,000 plus or minus. CTaSC does provide forensic services nationwide with local inspectors. For more information go to the Forensic Investigation Services by clicking here.