Line of cracks along tiles :(

[skipfeeney]

Hi,

About a year ago I got my kitchen tiled by a professional tiler. The tiles have started to crack along the joins of the 18mm WBP. The WBP was put down by myself. Looking back I have realised I laid it wrong - the long long crack is where the Plywood is 90 to the floorboards and not the joists. Could this be the reason? However near the hallway door there is also several cracks and the Plywood join was laid parallel to the joists there.

Is there anything I can do to attempt to fix it - I have only 1 box of tiles left to to use to attempt to salvage something and now the wife wants to put the house on the market!

Also potentially there could be a couple of other reasons...the tiles were cheap British Cermic tiles from B&Q, The professional tiler used Wickes Adhesive?! - I only realised this later when I cleared away some of the rubbish.

Long crack across kitchen floor:

Hallway door, cracks running in different direction:

Any help, advice, lessons learnt much appreciated!
Thanks

 

[SJPurdy]

Not really enough info to diagnose the cause.
18mm ply is a method of constructing a substrate to tile on if fitted over appropriate dimension joists at 300mm centres. Even then it is advisable to overlay this with a second layer of ply (10mm I think or a tile backer board) with staggered joints (to the first sheet) if the floor is more than 1 piece of ply. If overlaying an existing floor (eg T&G boards) then this existing floor must be reasonably fit for purpose (load bearing etc.), and the final over-layed floor, rigid and deflection free to be suitable for tiling. I have seen several hall floors that had massive deflection in them (due to inadequate and widely spaced joists) that would not be suitable for tiling even if over-layed with 18mm ply. The first picture shows (I think) cracking in the tiles over the joint between the sheets of plywood - I would associate this with deflection in the floor being concentrated at the joint and hence the cracked tiles. I can't really see what the cracks line up with if anything on the other picture. If the adhesive had de-bonded from the ply then the tiles would not have cracked, it is more likely that they would have become loose; the grout around them cracking and breaking out; and then finally if still trafficked/loaded breaking up. Personally I do not see that brand of adhesive (Wicks in this case) would be the problem assuming that the adhesive was specified as being suitable for tiling a plywood over-layed floor.

 

[Time's Ran Out]

Yes it's all down to preparation!
Plywood is not the ideal substrate for tiles and especially British soft biscuit tiles. There will be shrinkage/movement of the sheets and that caused the cracking.
If your moving the next people will no doubt put a new kitchen in sooner and any repair you attempt will look shoddy. Best Buy a cheap floor covering and cover it.

 

[skipfeeney]

Cheers all. Its already got a new kitchen . Might have to take it up and put laminate down. I am surprised the tiles have cracked so easily.

How do i prevent this happening in any future work? I guess I need to lay it 90 degree to the joists. I have read in some forums of people leaving a gap between plywood sheets. Is that a good idea? also some people screw it through to the joist? Are British tiles really that bad?

 

[SJPurdy]

I guess I need to lay it 90 degree to the joists.
I have read in some forums of people leaving a gap between plywood sheets. Is that a good idea? also some people screw it through to the joist? Are British tiles really that bad?

 

[SJPurdy]

I can't see how laying the boards with the long dimension at 90 degrees to the joists would make much difference. With the limited info I think it is the floor that is too weak/un-rigid that is the problem - it is bending under the weight of someone walking on it and the bending is concentrated at the joints in the overlaying plywood which leads to the tiles cracking.
Some tiles specified for floors (made by several nationalities!) are like a traditional wall tile construction ie. they are a soft biscuit with a surface glaze/finish applied. These are not as strong as the hard body with surface finish or porcelain tiles and in my opinion are not suitable for tiling a timber floor - I have had the same problem with them, cracking over the joints in the overboarding.

 

[Dumbo]

I always double ply floors instead of using 1 sheet if done correctly you do not get a continuous joint running up from bottom to top of substrate then install movement membrane prior to tiling .

 

[WetSaw]

also some people screw it through to the joist?

How else is it going to stay down? Did you not screw the boards down?

 

[Just Rizzle]

ply is the worst thing to put tiles on if you put down ply you need to put a decoupling mat over the ply to take a way the forces that cause the tiles to crack along the joins

 

[Dan]

Wickes sell Mapei i think don't they?

 

[Canyondust]

Yes; and offer on some grey rapid recently too (think Screwfix has similar range).