Grout cracking

[bluerover]

I have been doing a repair job in a bathroom, some tiles needed replacing and a re-grout. The tiles are porcelain on 6mm ply, screwed down correctly (according to my customer). I used Mapei waterproof grout, but as soon as it starts to dry it starts to crack. Has anyone any suggestions?

 

[bigandy]

first i am assuming floor?
could be several reasons. movement from under ply( not the correct thickness as per recommendations).are you using flexible grout?was flexible adhesive used?is tile stuck?are you mixing as per manufacturers?what make of adhesives/grout are you using

the more info you can give us the better response we can give

 

[bluerover]

Yes its floor. The ply was 6 mm rather than the 9mm I normally use, but this was a repair job - I didn't do the original. However, there was negligable movement as there were more than 4 screws per sq ft. I used Benferfix flexible adhesive. Tiles stuck well. The grout was Mapei waterproof grout. I bought this from my local supplier. I asked for Epoxy grout as it is in a wet area, (shower), but he didn't stock that and said the Mapei waterproof was as good. I never checked its flexibility. Maybe that's the answer. Thanks for reply.

 

[doug boardley]

my first impression was that it hadn't been screwed enough,but having read your reply to bigandy it does sound like grout isn't flexi

 

[DHTiling]

Which mapei grout is it..?...there isn't one called waterproof...???????

 

[grumpygrouter]

I suspect the 6mm ply is still the issue. Ply is used to strengthen floors and I recon there is probably deflection causing the cracking. 6mm ply in my opinion is a waste of time and can potentially cause problems in itself.

 

[Big B]

The Plywood all the way. Far to thin.

 

[tile55]

deflection, bounce and movement will all cause tiling failures. ie grout cracking and eventually tiles debonding.

 

[White Room]

Grout will only stretch so far, The word "flexible" can sometimes be misleading

 

[Fred]

12mm ply, the least................