Cracked tiles on big floor

[merit]

Got you 3fall 🙂

 

[mma]

Hi all
Just had a call from a customer who's floor was finished two weeks ago
Tiles are 900 by 900 porcelain
Fully bedded ,back buttered installed correctly
The l shaped cuts around certain walls have cracked
First thoughts were expansion of floor, but tiles go under dot and dabbed walls around perimeter
Under kitchen units , and there are a number of silicones movement joints around doorways ect
Floor is block and beam with insulation under floor heating and screed
Screed is rapid setting dry mix
Screed was ok to tile as far as moisture
But builder had to level floor prior to tiling by mechanically scraping the screed to get it level
It's not something I've come across before
All input apprceciated

Did you use clips?

 

[merit]

Yea clips were used
Took a few tiles up today's
Adhesive stuck to tile and bond to screed was sound
All day to remove 3tiles and clean adhesive from screed
Further inspection of screed ,this seems very brittle for a sand and cement screed, when chipping adhesive away the top was coming away
Around the edges the screed is no more than 40 mm in places and a small void is apparent between underside of screed and Dpm
Has the screed curled as it has dried due to uneven thikness
Screed has been down 5 months

 

[Ajax123]

I'm guessing it will have curled at that depth but also might be an apple pie. Compacted well at the top but not underneath so the top is strong but comes away from the underneath which is weak due to lack of compaction. We call it the apple pie effect. Its a very common problem ith semi dry screeds.

 

[mma]

Yea clips were used
Took a few tiles up today's
Adhesive stuck to tile and bond to screed was sound
All day to remove 3tiles and clean adhesive from screed
Further inspection of screed ,this seems very brittle for a sand and cement screed, when chipping adhesive away the top was coming away
Around the edges the screed is no more than 40 mm in places and a small void is apparent between underside of screed and Dpm
Has the screed curled as it has dried due to uneven thikness
Screed has been down 5 months

I did a 40m2 600x600 floor without levelling clips, had a few L cuts, and no issues. Did the utility room next door but used levelling clips, and there are hairline cracks on the L cuts. So my thinking is that the clips have put too much tension on the cut tiles.