Firstly happy new year to everyone.

I tiled a bathroom floor about 6 months ago and have had to repeatedly regrout it as the grout keeps cracking and coming loose. I was wondering if anyone could advise me why this is and how it can be remedied please?

I ply lined and primed the floor prior to tiling. I then used Johnson's one part flexi adhesive and Johnson's wide joint grout?

Thanks in advance.

It sounds like you have deflection issues. What thickness ply did you use?

12mm screw at 300mm intervals.

How bad was the deflection before you ply lined it? Should really have been 15mm minimum to keep within British standards.

I also never go as far as 300mm, for the time and the sake of a few screws i do 200 max and usually add a few in between for good measure.

6 inches is what I typically place the screws at and I will tighten that to 4 in places that need it.
But the floor is made up of more than the secondary sheathing board.
Foundation/main beams, Joists, crossbracing, primary deck are all vitally important to a good tile job.

It isn't just enough to throw down some ply or backer and then tile away.

On several occasions I have had to open up ceiling in basement and install I-beam support and additional teleposts to support the weight of stone being installed, and have had to many times make adjustments to the main beams of the house prior to installing anything.
Sometimes this means cutting up the primary deck to expose floor joists, maybe replacing joists that are warped (excessive crowning or put in upside down), installing crossbracing or even adding additional joists.
Typically this is not needed for the majority of jobs, but each job is uniquely its own and has elements that have to be assessed before just tossing down the tiles to ensure longevity and a quality job.

The ply was fixed to the exsiting weyroc flooring which I had added extra screws to, to take away any spring. If we agree it is a deflection issue is there anything I can do other than take the tiles up and start again?

Is there access to the underside of the floor from below or is the basement finished?

No it's a finished ceiling below.

Just how solid was the floor after you laid the ply ?
Was the grout flexible or standard ?
What tiles did you use?

Originally Posted by Sir Ramic

Just how solid was the floor after you laid the ply ?
Was the grout flexible or standard ?
What tiles did you use?

Agree with sir, we need more info to give better advise

Ok the floor was solid there was an area of spring on the weyroc prior to overlaying it with ply. I screwed this at very tight intervals. I then overlayed with the ply and added extra screws in that area. I felt the floor was solid and wouldn't cause me any deflection issues. I then used Johnson's wide joint grout. I've just looked through my invoices this wasn't a flexi grout, would the use of a flexi grout solve the problem? The tiles are just a bog standard ceramic floor tile.

hi,have you re grouted both times in non flexi standard grout jon?

and are any tiles showing signs of movement or is it just the grout?

Ok then you cant really expect a standard non flexible grout to work on a timber floor. You will need to remove all the grout and hoover joints clean then regrout with a polymer modified flexible grout or a standard grout with an Admix.
I would use Mapei grout, never had any issues with cracking.

The tiles are solid it's just an issue with the grout. I did use a non flexi grout on the floor. I will take your advice Sir Ramic.

Thanks for your help everyone.