Grout Cracking despite rakeing it out and doing it again

[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

 

[Flintstone]

Almost certainly movement in the floor. How thick was the ply? Tiling onto any wood is best avoided. If you start as you mean to go on an refuse to tile onto ply, you will have a lot less issues. Cement board is far better. Can’t comment on what’s under the ply

 

[Weebisto]

Almost certainly movement in the floor. How thick was the ply? Tiling onto any wood is best avoided. If you start as you mean to go on an refuse to tile onto ply, you will have a lot less issues. Cement board is far better. Can’t comment on what’s under the ply

Really good advice thanks

 

[Ajax123]

Large joints heating on full bung.... recipe for drying shrinkage cracks

 

[Weebisto]

Large joints heating on full bung.... recipe for drying shrinkage cracks

Thanks for that @Ajax123 I'm fairly early on in terms of experience but it was one of the few variables that was different to anytime before and grout has always dried nicely up until now. And heating was on full bung as I lost 3lbs which helped the diet!

 

[Time's Ran Out]

Heating on full bung - that in itself should cause concern.

 

[Perry]

A heated floor?

 

[Tile Marble Granite]

Dont walk on it. It will not crack, lol

 

[Qwerty]

@Weebisto correct me if I'm wrong, but you dont seem to be having too much luck with tiling!? At the start of the month you posted this thread-
After a knock to confidence, back at it tiling a floor - https://www.tilersforums.com/threads/after-a-knock-to-confidence-back-at-it-tiling-a-floor.85106/#post-890700

and said in there .....

Back in the saddle this week with an ensuite floor that needs old adhesive removed, backer board installed and sealed then tiled. Using Mapei Keraquick with 100% coverage and will be working from a centre point and using tile levelling system.

Any words of wisdom? This one has to go well

Why did you chose to tile to wood when you knew backer board was the correct method. There was plenty of pointers for you by members in that post.

My advice to you is to know your limits and proceed with tiling with caution. You have had problems with a couple of jobs now and run the risk of doing your reputation more harm than good. This latest floor will keep failing (with movement) and you will have to take it all up and start again. But who will pay for this, you or the customer?

 

[Bathfix Bob]

[Distant sound of gunshot]

I know the last time i tiled on plywood floor it failed and that was 2010, I did tile an 18mm plywood countertop for a basin this year and due to thickness constrains I couldn't add another 6mm so i had to tile straight to the ply and i remember the grout cracked as soon as it dried with no weight on the countertop.

God knows what that was all about.

 

[macten]

What's Mapei latex sealer?

 

[GAZ5518]

Cracking probably due to either movement or delamination...I will always prime floor at least twice and then Bal rapid mat on any ply I come across failing that 6mm hard I backer or the like...
Flexible adhesives and grouts whilst a must, can only deal with a certain amount of deflection etc..
Once again ....as the others will tell you ...preparation is key...