Screed ordered but rework required

Just to clarify: There is no ready-mixed screed based on concrete! It is either screed or concrete – both groups differ firstly in the grain size of the mineral aggregates and further in the different installation methods. A ready-mixed screed is now referred to as "prefabricated screed," these are the so-called "dry screeds" or rather OSB or gypsum fiber boards. However, we assume that a mineral cement screed was installed. That it develops cracks at corners or edges during the construction phase should not happen, but it can. Then the screed is simply repaired at the demolition points. At corners, it is removed and replaced by a synthetic resin screed. But tearing out the entire heated screed just for that would be completely disproportionate! And would not be supported by any expert in the field of "screed work"!!
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Regards: KlaRa

The screed has now been completely removed. Because it could not be ensured that it would not cause problems in the future. Every corner is broken and it gave way significantly when subjected to heavy load. I think the contractor himself was not sure about this and the costs would have been much higher if the screed broke after moving in. The new screed is supposed to come on Monday. Hopefully then without problems

The screed has now been completely removed. Because it could not be ensured that it would not cause problems in the future. Every corner is broken and it gave way significantly when subjected to higher loads. I think the contractor himself was not sure here and the costs would have been much higher if the screed broke after moving in. The new screed is supposed to come on Monday. Hopefully then without problems

Did the contractor hint again at WHAT he thinks the cause is and accordingly WHY the new screed will not cause any more problems? Several here did not find that it was due to heating during drying plausible (I don’t either, but I’m not knowledgeable on the subject).

Did the contractor hint again at WHAT he thinks the cause is and accordingly WHY the new screed will no longer cause problems? Several here didn't find that heating during drying was plausible (neither did I, but I'm not knowledgeable on the subject).

According to him, probably the heating issue.
Also, the substrate was very soft.
A very soft material on which the underfloor heating was stapled.

The screed has been very crumbly from the start.

Is this the first screed he is installing? Underfloor heating systems are often laid on "soft" styrofoam boards, after all the pipes are stapled down and the plastic stapler things are supposed to hold. And underfloor heating has only been widely installed for a few years, and before that the respective screed also dried. It sounds more like he messed up the screed mixture himself and now wants to pass the buck to someone else...

Too little water or too little cement or too much sand (take your pick). Or cement too old.