Grout cracking - Tile Advice

[gary.tolley]

Good morning all,
Been to see a job and the grout on the bathroom and showroom floor is beginning to crack. It's on a timber floor with a decoupling membrane ( deco matting I think it is called )
There is a section not tiled and the matting seems well stuck.i asked to
See to grout and it is kerakoll but it doesn't mention that's it's flexible or
Give any indication that it's suitable for timber flooring.the tiles are ceramic and seem well stuck. I'm puzzled and don't want to charge to rip up and re do the floor if is simply a grouting issue.
Any advice would be appreciated.

Floor

 

[Andy Allen]

How much is the floor flexing...?
Dose the grout say an additive can be added to make it flexible? If so do you know if any was added to the mix?

Could just be wrong grout used, this would cause cracking, however a decoupling mat is more for lateral movement than deflection....I would be checking for any loose tiles and find out more about the subfloor..

 

[gary.tolley]

Thanks for your reply mate,the customer told me she noticed
Slight cracks straight
After it was grouted but when I was there there was major road works taking place and I could feel the vibrations through the house.on the technical specifications of the grout it says an admin can be added but no where does it say it can be used on timber floor or that it's flexible .the tiles are solid and it all seems well stuck . I've always be told that the deco matting will take the movement and even if it comes away from
The floor the tiles and grout shouldn't crack as it acts like a floating floor and in the 15 years I've been doing this never seen this happen.

 

[Time's Ran Out]

It wouldn't crack if it was solid so there must be movement somewhere.