Cracked grout, uneven floor tiles on new isntallation - help!

[Helen72]

Hello, I have got a problem with my recently laid ceramic tile floor (laid by a tradesman not by me) as the grouting is now cracking and in some places bits have come out. Can any one advise what the problem and remedy may be?

The (black) grout looked virtually liquid when the tiler put it on. he told me to mop the floor the next day to remove "dust" from the surface of the grout which I did. however when it dried after mopping it still looked "dusty" and the colour was an uneven mid-dark grey, but I didnt notice any cracking at first. the spacings between the tiles are 3mm.

The floor construction was previously a floating floor and the builder advised that we would need to redo the subfloor before tiles could be laid. they took up the existing floor, built a framework of battens on top of the concrete blocks, insulated between the battens and laid waterproof chipboard on top of that and then (6mm I think) plywood on top. Does this sound like a suitable base for tiles?

thanks for any advice you can give.

[grumpygrouter]

6mm ply is absolutely no use for tiling onto and this may well be a big part of your problem. I personally also think the grout joint is too tight for a timber floor. Do you know what adhesive and grout were used as this can also have a bearing on your problem?

[Helen72]

Im afraid I dont know what adhesive and grout were used - but can you advise what the correct type would be? Also if they should not have used 6mm ply, what should they have put down instead? Finally, what would you suggest should be done to put this right?

many thanks.

[Diamond Pool Finishers]

get them back to sort it helen, i agree with grumpy

[Helen72]

yes they are coming to sort it out - I just wondered what would be the right solution?
as they caused the problem you can understand I am not that confident in their ability to solve it.

[grumpygrouter]

The builder was correct in trying to cover over the chipboard but unfortunately 6mm ply is just to flimsy. They would have been better to use a 6mm cement based tiling backerboard or a more substantial thickness of ply (12mm abso. minimum really). The adhesive should have been a cement based flexible adhesive and so should the grout.
IMO you (they!) will have no alternative but to rip it up and start again, as a "repair" is unlikely to be successful.

[Helen72]

The builder was correct in trying to cover over the chipboard but unfortunately 6mm ply is just to flimsy. They would have been better to use a 6mm cement based tiling backerboard or a more substantial thickness of ply (12mm abso. minimum really). The adhesive should have been a cement based flexible adhesive and so should the grout.
IMO you (they!) will have no alternative but to rip it up and start again, as a "repair" is unlikely to be successful.

OK I will check what materials they used and see what they say. thanks a lot for your help.

[smurf21]

The Grout cracking so soon does sound like a deflection problem ie the floor they have redone with timber bearers may not have enough supporting noggins in or enough packing under the joists if they have tried to level the floor. they rightly covered the chipboardas this is no good for tiling onto but as grumpy said 6mm ply is not the right choice should have been minimum 15mm and as you cant get 15mm ply then 18mm is the better option now normally i would advocate using a 6mm tile backer board onto the chipboard, but in this instance i think the floor reall does need the deflection taking out of it first, just regrouting isnt going to solve this prob. Imo it needs ripping out back to the joists and re fixing with more support 18mm ply straight onto the joists rather than the chipboard the a tile backer board onto the ply either No more ply or hardi backer boards then re tile using a flexible tile addy and flexible grout.

The colouration problem on the grout could be inconsistancy with the mix ie to much water to powder ratio...