Tiles Cracked in New Extension - Help Please !

[DAK]

I think I posted this in the wrong forum so here goes again...

We have had a single story extension done to our house which has left a 40M2 kitchen area which we have tiled. The problem is that the tiles (10mm thick from B&Q) and grout have cracked in line with the wooden joists which are under the floor.

In terms of the build my understanding is the following:

- Wooden joists are in place under the floor with some noggins and two areas where it is bricked to re-inforce. There is concrete underneath the joists.

- On top of the joists are insulation and then underfloor heating has been laid on top of this

- Chipboard engineering grade tongue and groove chipboard has then been put down to board out and has been screwed in (this and all of the above was the responsibility of the builder)

- The tiler has then laid and (I think) used adhesive to stick down a Ditra mat then laid the tiles on top using flexible adhesive and fully buttering the tiles.

The tiles and grout have cracked in parallel over where the joists appear to be - we now have a situation whereby the structural engineer has looked and said he doesn't think it is down to deflection from floor as the tiles are cracked along the line of the joists rather than horizontally across the tile (see pictures attached). so we are re-laying some tiles and re-testing if there was some settling movement. Personally I think the floor is a little 'bouncy' but given the structural engineer has said he doesn't think it is down to the building work the builder thinks he has delivered.

Would a layer of plywood or cement board on top of the chipboard have helped here?

Other suggestions welcome and appreciated and apologies for the long post !

 

[DAK]

120cm apart cracks suggests along the joints in chipboard rather than joists which would be maximum 60cm apart but mior like 40.

Thanks for the insight. In terms of resolution of this do we need to do something with the chipboard floor? Obviously we need better tiles. Would ply or cement board resolve?

 

[Tile Marble Granite]

Suspended floors speaking, the joist is the most important, the bouncing comes from the joist, 18mm ply is a must as chipboard is totally unacceptable for a floor, lol. As far as I am concerned cracks are related to bouncing

 

[david mccullough]

you say that the floor is 40m2, that's a big room, is it 4mx10m, 5mx8m?
7"x2"joists seem a bit light for that size of room unless there is support walls, in the correct places, the quality of the tile shouldn't come into it, or the use of chipboard, i take it the tiles aren't boast? in my experience the better quality the tile the more brittle the tile, the main problem is movement, the fact that it still cracked even with ditra is surprising, there must be too much movement,
fill a glass of water, set it on the floor where there is the most movement and bounce on the floor, if if there is any more than mild ripples the floor isn't supported enough

 

[Slippery]

a 7 inch joist will shrink by around 5-7mm when brought in from the builders merchant under normal conditions, put heated pipes next to it and you could expect maybe another couple of mm, that's what I suspect may have happened but the tile choice is the bigger part of the problem IMHO

 

[Nigel cheltenham]

I’m a joiner 40 years I have always overlaid chipboard with 18 mm exterior grade ply screwed and fixed every 150 mm lay ply opposite way over chipboard I personally would never tile onto chipboard as I think their would be too much movement in floor

 

[demi34]

They should put hardie boards on the floor stuck with adhesive and plenty of screws