Grout Cracking despite rakeing it out and doing it again - Tile Advice

[Weebisto]

hi all, did a bathroom and a kitchen floor this week. Used standard set addy which gave me a bit more time to work. Left it for a good 24 hours before grouting Plywood subfloor installed by joiner and sealed with latex sealant by me before being left to dry and then tiled. Grout in bathroom fine but grout in kitchen showing lots of cracks. Went back in today and mixed grout a little thicker in case that was the issue, raked out affected areas, cleaned and re-grouted. Been back to check and although not fully dry it's not as bad but still cracking has appeared. Heating on full bung so wondered if it's dried too fast? Alternatively, could it be movement on the sub floor?
Any suggestions appreciated

 

[Andy Allen]

Are the tiles loose..?

 

[Weebisto]

That was my first thought but they all seem sound

 

[Andy Allen]

What adhesive and grout did you use?

 

[Weebisto]

Larsen std set and mapei grout

 

[Rookery]

Almost certainly movement due to poor substrate prep. Or it could be wrong grout. Or it could be a few other things. We need the details of what tiles, how they were fixed, what with and what to.

 

[Andy Allen]

Is the adhesive and grout flexible...?

 

[Weebisto]

Almost certainly movement due to poor substrate prep. Or it could be wrong grout. Or it could be a few other things. We need the details of what tiles, how they were fixed, what with and what to.

Ok so tiles were ceramic from b&q 60x30, plywood subfloor installed by joiner, I sealed it using mapei latex sealer, fixed using Larsen std set adhesive 100% coverage and left for 24 hrs then grouted using mapei grout from Tile Giant....twice

 

[Tile seller]

Evening,
Mapei ultra colour? If so, then that's a good grout.
I wonder how thick the ply was and how well it got screwed down.
Sometimes by treading/pushing u can see the movement close/open the cracks.

 

[Weebisto]

Evening,
Mapei ultra colour? If so, then that's a good grout.
I wonder how thick the ply was and how well it got screwed down.
Sometimes by treading/pushing u can see the movement close/open the cracks.

That's another valuable lesson: never assume that a joiner has done a sound job on the sub floor - test it first

 

[GoneGuy]

Are the cracks near the joins in the plywood?
I would say there is a lot of movement in the ply

 

[Weebisto]

Is the adhesive and grout flexible...?

Yes - just checked to confirm

 

[Weebisto]

Are the cracks near the joins in the plywood?
I would say there is a lot of movement in the ply

To be fair after the second grout it's concentrated in a four tile area which was the first to crack the first time around.... which is leading me to think that there's some bounce particularly under that bit

 

[Tile seller]

It's unlikely but, I see 'Tile giant' sell KERACOLOR FF.
This one only goes up to 6mm joints. If u used this and the joints bigger, it's just the grout type.

 

[Weebisto]

It's unlikely but, I see 'Tile giant' sell KERACOLOR FF.
This one only goes up to 6mm joints. If u used this and the joints bigger, it's just the grout type.

Good call buddy but it was defo ultracolor