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Bathroom Fitting

Bathroom tiles


I have initially posted a question re freestanding bath and floor tiles and got some great advise from various tradesmen.

Now... following long period of waiting and discussing things with my contractor they are proposing the following to the cracked floor...

The problem:
Floor tiles have been put on 18mm ply which was screwed to the joints (they claim it was screwed every 90mm-100mm), flexible adhesive and grout was used and ceramic tiles (

The floor started cracking along the line where the 3 ply pieces were joint.

They claim it is either due to poor quality tiles or joints being weakened by removing original wooden boards from there (originally the bathroom has old wooden floor boards - it is typical 1930s terrace house).

Proposed solution by contractors:
They are reluctant to remove the tiles and make sure ply is secured to the floor joints properly as they claim they have done it (I have no evidence nor have seen the work in progress). They suggest the joints are weak and old and that's why the movement is happening - therefore the only solution they can see is to put 6mm ply on top of the existing tiles (and cracks) and then tile it on top of it....

so it will end up being 18mm ply, cracked tiles, 6mm ply, tiles again.... - is this a common practice or complete nonsense??? I would rather have the floor pulled and properly installed ply/tiles than creating layers in the new bathroom. The whole bathroom was originally stripped to the brick and everything has been installed new...

I am pulling my hair out as I write it as I think I had enough! ;)

Please let me know your suggestions, advice and what is a NORMAL correct practice in this situation.

Thanks a lot!

9 Answers from MyBuilder Bathroom Fitters

Best Answer

Hello Deidre,

Total rubbish.... the bottom layer of tiles will keep cracking, it will sound like you are walking on broken tiles after a while. Doubt the top ones will last five minutes, bearing in mind the sub floor is moving. At least they have admitted the joist are the problem. Tiles don't just crack on their own.

I will suggest you get a local floor layer/company to have a look... you can't lay tiles on a springy floor. Putting another layer of 6mm ply on top of the existing tiles, then more tiles is stupid.

Proper solution....The floor joists need strengthening/replacing, or others either put in between originals or along side fixed/bolted into them....floor needs to come up to do that.

Kind regards



Answered 19th Dec 2011


I would pull up the floor examine floor joists and go from there.
Sounds to me that the floor has flexed under weight, maybe full bath etc?
When I have pot new flooring down I will always aim to keep floorboards down as they are 23mm thick and do not flex on prepared joists.

Then ply 9mm to 12mm is laid on floor boards for a solid smooth surface to tile or whatever is desired.

Plying over existing tiles will add more weight to current floor and crack again.

Is the floor cracked under the bath?


Concept building services Kent


Answered 14th Dec 2011

Hello Deirdre,
As you can see from all of the responses you have had it is pure madness to try to fix the problem like this .
The only solution is to remove the tiles and the ply, re-inforce the floor joists re-lay the ply screwing at 6" intervals os less to en sure the floor is rigid, prime the floor with a floor tile primer and use a super flexible adhesive and flexible grout,
Your contractor is looking for a quick and easy solution, they don't exist!
Redards Cliff.


Answered 14th Dec 2011

STOP!!!!!! The only reason for the cracking is movement in the ply or the joists.The ply should be screwed every 6" in every direction.Any joints in the ply should be staggered.Ply should be primed with pva before tiles fitted with flexible adhesive.I suggest you get your builder to lift a few tiles around the cracked area and show you that the ply has been secured correctly.Under no cicumstances let him fit 6mm ply on top of existing tiles as this will be a total waste of your money and his time.
Good luck.


Answered 14th Dec 2011


Don't let them to tile on top of the existing floor. The floor needs to be removed, and if the joists needs to be strenghten it needs to be done. When it's sound then they can install the ply. To make it more stronger use a metal mesh on top of the ply screwed down and of course not wickes flexible adhesive to lay your tiles. Mapei, Ball etc.


Answered 14th Dec 2011

The one very important mistake with this floor is the joints in the ply that run at 90 degree's to the joists have not been supported.


Answered 2nd Apr 2012

this solution sounds ridiculous ,if its cracking take it up and secure ,put tile matting down first ,then adhesive and tile and grout


Answered 14th Dec 2011

The problem stems from the fact they have layed ply directly on to the joists.
When the ply wood sheets are butted up they don't lock together so that's a weak spot so if your tiles are layed over this weak point they will move with the ply so the grout will crack.
When I tile over a timber floor the floor boards always stay down and then I ply over the top using exterior grade ply at 12.5mm thickness screwed at 150mm grid pattern. Use a good primer to seal the ply then tile with flexible adhesive
And finish with a good quality flexible grout.
Fixing 6mm ply over already loose and cracked tiles will just add more problems and delays.
Get them to lift the whole lot or get someone else in.


Answered 14th Dec 2011

if the floorboards needed removing for access to pipework 9 times out of 10 they are usually not good enough to put back down. I always make sure the joists are solid, if not you can brace with timber noggins, then lay 18mm tongue and groove caberdeck flooring and screw directly onto joists, on top of this I lay and screw 12mmply at 150mm intervals. then a good pva and flexible adhesive. If a builder has done the job then possibly they have used nails instead of screws to secure the ply
all the best


Answered 4th Mar 2012

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