why have my ceramic floor tiles (on concrete) lifted?

[triniwalk]

I built a holiday home 8 years ago. The tiles were perfect for 3 years then a few shifted near one of the bedroom doors. These were replaced after checking the concrete slab underneath. 2 years later they lifted again plus 4 others on the side of the bed. These were again replaced after checking the slab. 1 year later we walked in after dinner one night to find that the 2 shifting ones which had been replaced the first time had not only shifted but when my husband sat on the end of the bed there was a loud crack where a line of 12 tiles had risen in a ridge on the near side of the bed. We had all removed and the slab inspected. There were no cracks, just perfect concrete. Why has this happened? I know one builder who walked in to find an entire flooring completely raised with all tiles helter skelter. Weird to say the least. Rising gas from concrete? tropical heat???

 

[gcol]

Did you leave a grout gap between the tiles or did you lay them edge to edge?

 

[nellyb]

What type of tiles are they? If they are porcelain and a suitable adhesive hasn't been used, it will not bond to the tile so basically all that will hold them down is the grout (that's if there are grout/movement joints)

 

[triniwalk]

Thanks for speedy responses. The builders did the floor tiling with me watching. (I did do the 6 counter and sink splashbacks though which are beaut) The entire area 30sq ft is tiled on concrete slab with reccommended tile cement from merchant. They supply everything from spacers for tile size and grouting. The first lifting was thought to be stale bonding cement, but then it lifted again. The second and third are mysteries as it was all new stuff. Not marble, either from Spain/Italy/Brazil as most imports into the islands. Hence I wonder if concrete put down 5 yrs ago would emit gases. This is only in one bedroom 15 ft sq. None of the other rooms have the problem thank goodness, as I need rental.

 

[noseall]

sounds like a case of sulphate lift to me.

red ash sub-floor, oh dear.