QUESTION

We hired a complete master bath remodel done by a contractor recommended where we purchased our filled and polished travertine tiles that now cover the whole floor, shower, and jacuzzi surround. The floor tiles are 16" square, and cover an 10.5'x7.5' area. The bath is on the ground floor over an unfinished basement. The floor is on 16" floor joist. The contractor pulled the old carpet, laid (screwed) a grey concrete board to the plywood, installed the electric radiant floor wires on top of the grey board, and then poured a self leveling thinset over the grey board and radiant heat wires. The travertine was back buttered and laid on the floor. This job was done in December and took about ~4 weeks to complete. Once the job was done we turned the radiant heat on and all was fine until the day after we turned if off in April, when the next day we noticed a cross shaped crack that runs the length the 10.5' length of the floor, and crosses it at right angles about half way, running most of the 7.5' length. I wanted the installer to use the Schulter DITRA uncoupling membrane, but he didn't have experience with it and talked me out of it saying it wasn't needed. I also noticed that when he poured the self leveling thinset over the grey board and radiant heat wires, some of the wires were completely covered, some were not, only covered 1/2 or 3/4 of the way. It has been a year and a half since the crack appeared, and no others have appeared anywhere else. My questions are: 1) Can I have just the cracked tile replaced? 2) If so, I assume it will destroy the radiant heat wires - Can I run new radiant heat wires between the floor joist on the underside of the floor, in the ceiling of the unfinished basement? 3) If I will have to replace the whole travertine floor, would you recommend I use the Schluter DITRA uncoupling membrane? Thanks for you advice.

ANSWER

ANSWER - I assume there was a wood subfloor under the carpet.  The cementitious backer board should have been glued and screwed every 8" to the subfloor.  The 3x5 foot sheets should have been staggered from each other to make the floor more stable.  The joints between the backer board should have had a 1/8" gap and been filled with thin-set and taped with alkali-resistant glass fiber reinforcing tape per backerboard manufacturers' directions.

Chances are that the cracks in your travertine line up with the joints in the backerboard because it wasn't installed correctly.  It is possible that you have too much deflection in the floor that could contribute to the cracking problem, although 16" o.c. floor joists should be adequate.   If you don't have any movement joints, filled with an ASTM C920 sealant, at the perimeters of the room that could contribute to the problem as it may not have been able to mitigate the thermal movements from warm to cold.

You should be able to repair the floor if you remove the cracked tiles carefully, and try to avoid damaging the floor warming wires.  If you do damage them you might be able to repair them.  If you did substantial damage to the floor warming wires you can purchase an Under Floor Mat floor warming system that is installed between the floor joists.

If the cracks in the floor are consistent you could open them up with a dry diamond cutting blade and fill the open joints with the sealant, although this doesn't fix the problem and is only treating the symptom.

I don't see any need for using an uncoupling membrane as long as all of the other preparations and product installations were done correctly.