marble tile cracking

I have a bathroom that I have done completely in marble tile. I have 2x12 floor joist on 16" centers. 3/4" osb with another layer of 1/2" osb on top of that. I then put down 1/4" hardi backer. I put down 12x12x3/8 marble tie down. Every where there is a seam in the hardi backer the marble tile is cracking. It is only cracking on the floor. It is not cracking on the walls or around the tub where it s vertical. Did I do something wrong and is there any way to repair the tile? I hope I do not have to tear it out and start over. Thank You to anyone who can help me.

First thing you did wrong was not tape the seams with the fiberglass tape. If the joints are not taped the tiles that fall on the seam will crack, maybe not right away, but it will happen. How did you install the Hardi board?

Yes as was stated above. Did you thin set the backer board down and nail at the appropriate intervals? Proper install means thin set under the board before nailing it down. Hardi recommends a gap of up to 1/8" between sheets and fill the seams with thin set and fiberglass tape over that with a skim coat over the tape before tile. We usually 'dry" fit a room before securing it down, meaning we cut it all and lay it in place making sure the cuts are correct first.

I guess I really screwed up. I did not thin set the backer board down. I used backer board screws to hold it down and I put them about every 6". I butted them as close as possible, but I did not tape the seams. Can I fix this by taking up all of the tile over the seams and tape and mud the seams? Then relay new tile. If I can do this should I leave them butted or should I cut a small gap to fill with mud. Do I need to completely start over and put down the backer board with mortar underneath it? Thank you for the help I appreciate it.

I forgot to add that I used a tube of liquid nail on each sheet of hardi backer. I do not know but hopefully that is good enough that I do not need to rip all of the hardi backer out and start over. Hopefully I can just take out the tile on top over the seams and seam tape it then relay the tile. Thanks again for any help that you can give.

In all honesty you should have used unmodified thinset underneath the boards, not liquid nails. The purpose of the thinset is to take out any deviation from underneath the boards. If it was me I would rip it all out and do it again. Since I am not you, you could rip out the tiles that fall on the seam and tape the seam and hope that it works. In the end it is your money that would be on the line. If the marble wasn't too expensive then please rip it all out and redo it the right way. This way in 5 years you can look back on this as a learning experiance and appreciate the hard work you put into doing it right.

The Liquid Nails is the cause of the problem. ALL cement board makers say to use thinset to fully bed each sheet. The taping of the seams is also crucial but to tape the seams now without removing the cement board would be a waste of time and money.

I was wrong I liquid nailed the 1/2" osb to the 3/4" osb. I only screwed the hardi backer down. I found this out when I started tearing the tile out.

That wasn't a good idea either. Construction adhesive creates voids where the beads aren't. Makes matters much worse. No adhesive to install underlayment, unless you can use a thin wood glue and laminate them with 100% coverage. And, only fasten underlayment to subfloor not to joists.

Jaz

Use Akemi and fill the cracks it will look natural if you do it right. Look at the marble bathroom pic in my photo gallery. I had to use it on the back wall. Find the spot. I challenge you. http://www.mikebocktile.com/

[Edited by mikebocktile on Sun, Jul 19, 2009 at 9:13 am EST]

I'm going to say it's the in the first page, third row, middle picture. Titled "light brown shower tile from Florida tile 2". In the picture it's the middle row, back wall, six tiles up, starting from the bottom. In that tile there's a blip about 2" down, towards the middle of the top part of the tile. Looks like it's about the size of a quarter. Did I win?

Use Akemi and fill the cracks it will look natural if you do it right. Look at the marble bathroom pic in my photo gallery. I had to use it on the back wall. Find the spot. I challenge you.

Not to be a wiseass, but is that when you're taking the picture, or after it cracks again?

Look-- I'm not trying to jerk your chain here. The long and short of it is that the cracks are a symptom, not the problem. Fix the symptom, and it's only going to happen again. Maybe in a slightly different spot, depending on how hard the material is you used to fix the original cracks (and Akemi IS much harder than the stone, so it would most likely delaminate from one side or the other, rather than cracking), but it WILL crack again. The only way to fix it permanently is to trace it back to the source of the movement. In this case, it's the lack of thinset under the cement board, coupled with the lack of mesh tape. You then fix the problem, and put it all back together. PROPERLY. Not glued together.