Travertine HELP

[macaroonie]

Hi gang I'm a newbie here and hope someone can help. I did a google for Travertine help and landed up here , so here goes.
I do total bathroom renovations and on a recent job the client took a fancy to a large 600 sq travertine. its about 18mm thick. These were laid on a very stiff WBP 1" ply floor. The floor has a 8mm heating trace inset linked to the towel warmer.
The tiles were laid with a flex dry powder adhesive ( bal if memory serves ) and grouted with Mapei flex grout.
Here is the problem. All was well for 3 months or so and then gradually some of the tiles have split. Strangely the splits follow the joint lines between the plywood. The ply and all the floor is very solid as the owner is a big laddie.
The ply is screwed down to the joists and the joists are reinforced with props to the solum, so it is all very stiff with no 'bounce'
My initial thought was that the heating had caused the issue but there is a tile that has no heating under it that has split also, so that kind of rules that out.
There are also tiles with heating that have not split.
The only thing that I can think of is that the tiles may have shrunk somewhat. Could it be the case that if they had been stored outside or in damp conditions that they would behave in the same way as timber ?
None of the tiles have come loose in any way.

I hope someone can throw some light on this for me as for now I am at a complete loss.

Thanks in advance, Mac

[pjtiler]

thats a tricky one
you say the tiles were stored outside could frost have damaged the tiles trav is very porous and brittle

[macaroonie]

hey there thanks for the swift reply. Actually I got them from B&Q , I spotted them in their garden masonry section specifically for a hearth for a woodburner in my own house. I was doing the bathroom at the same time and showed the tiles to the clients. They thought they were fab so in they went. I'll slot in a couple of pics here so you get the idea.

[Stonebro]

Seen it many times before and is the main reason I will not let any of my tilers use plywood. Plywood brought in from unheated wood yard has moisture content x%. House has moisture content y%. Underfloor heating shrinks/expands plywood and crack along every join.

worst news is, it generally carries on until every piece of plywood is framed with a hairline crack

Learn as I did the hard way, and switch to Wedi / Hardibacker / Nomoreply tilebacker boards - more susceptible like plywood.

Everything contracts and expands concrete needs movement joints, tiles need movement joints. Timber though expands contracts more than your tiles do .

4 years ago we made a complete switch to engineered boards . We have not had a single problem

[Stonebro]

Sorry it this heat !! Should read

Learn as I did the hard way, and switch to Wedi / Hardibacker / Nomoreply tilebacker boards - more dimensionally stable than plywood.

[wetdec]

The best and recomended way that this latteral deflection can be avoided is to lay Durabase CI HERE or Schluter Ditra mat HERE over the ply before laying your tiles, the difference between the two being the CI mat is cheaper "end of cracks"

One of these mats should always be used when combining screed installed underfloor heating with stone on a floor !!!!!

tiler

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[macaroonie]

Wow that was fast. I participate in a loudspeaker oriented forum dedicated to JBL products and the knowledge base that is behind it is astounding. Same here also it would seem. I have done the underfloor thing many times with vitreous ( often quite large tiles )and had no problems.. Since I will have to replace the broken ones would you expect that the ply will have done its shrinking by now and be stable such that I can ONLY replace the breakage. What about if I reinforce the joints with GRP mat.
As you can imagine I would prefer not to have to renew all of the floor.
Thanks so far, I will have a look at these backing mats also.

[wetdec]

You will be lucky to get away with it, Ive seen trav cracking a year down the line, different people, different houses, different adhesives the adhesive is stronger than the stone its as simple as that.

tiler

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[macaroonie]

So here is the dumb question for this week, All over the Med you see that type of tile laid in plazas , patios , pool areas etc. How do they get past the extremes of temp. etc.

[wetdec]

They dont lay it on ply LOL its the latteral deflection caused by shrinkage or bedding in that would seem to be at the bottom of your particular problem

tiler

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[macaroonie]

Thanks a million. One last question , I had a quick look at the WEDI site and I see they do boards 2500 x600 x 40/50/60 thick. I presume that I can use these in the future where I have been using WBP ply ?

[wetdec]

Hey ask away I can only try and help that way !!

Your talking to the wromg guy I will certainly sell you a backer board and lots cheaper than wedi but I am a believer in screwing and gluing so personaly would always use ply. In this case I would of overlaid the first ply with a second travelling in the opposite direction so avoiding any transition cracking where possible.

tiler

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[pjtiler]

looking at your photo,s
the floor joist,s look very suspect
its obverse there been a fair bit of movement somewhere
i,m afraid the lot will have to come up and a lot of strengthening will be needed
then as the lads say use some sort of backer board

and leave B&Q to the punters eh

[macaroonie]

What is the script with type2 chip vis a vis shrinkage. I think you can see where i was going with the construction and the 25 ply was to accommodate the large chap in the house and the end height came out good too with no awkward transition at the door. I am a little bit at a loss as to why 2 x 12.5mm ply laid alternate directions would help given that the laminations of ply are at right angles. However if it has worked for you I must defer to your greater experience. I am after all the dunce with the problem.
Actually I do more carpentry/ joinery work than tiling and it is the case that a lot of the ply coming in now is from China and to tell you the truth I do not like it one bit.
I think I will take a punt and lift the damage , hope the shrinking is all done, reinforce the joins and re-lay.
The shrinkage should be well gone by now coz the heating trace is on all the time and that is about 8 months in total. The solum is as dry as a bone too.

[wetdec]

If you have 2 sheets of ply meeting on a joist you have a hinge if you then board in the other direction you no longer have a hinge as the joint is crossed so it reduces/prevents transitional cracking


tiler

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[macaroonie]

Thanks everyone for all your help.

[Stonebro]

Wedi board / Marmox - 10mm thickness
NoMorePly - 6mm thickness
Eziboard - 6 or 8mm thickness

All have good insulation properties as well. Wedi board is stuck down with Single part flexi - I screw and washer at 300mm centres and then tape joints.

Nomoreply stuck down with a thixotropic polyurethane glue and 8 Screws per sheet.

I have used schluter many times as well - all are good well researched and 'stable' systems.

A lot of people compare them to ply price wise generally they are all slightly more expensive to buy but generally all are very easy to install