problem with a screed floor

[runci21]

ive layed a screed floor in my bathroom at a depth of 25 mm as per building plans , its bean layed for a month and is cracking badly and i have some doubts if it is sticking to concrete below ,
concrete is 5 inches thick and was layed 3 months ago .
i did not use any sealer on concrete on plasticier in screed , where have i gone wrong ????

 

[noseall]

25mm thick.

the thinnest i've seen it specced is 50mm. the norm is 75mm.

no wonder it's cracking.

 

[Nige F]

that`s not a screed, it`s a horizontal render BUT my house is done like it ,so it`s possible , not a good idea, but possible ........built c. 1958 hope this helps