Creaking screed in the area of expansion joints, some joints creak, some do not. The house is newly built, monolithic.
Intermediate floor slabs with a thickness of 180 mm. Screed executed by the builder, made of cement-sand mortar with polypropylene fiber, ~ 50-60 mm thick. The screed is laid on 25 mm thick Isover boards. Around the perimeter on the walls is laid with a kind of foam tape about 8-10 mm thick.
In the doorways there are expansion joints. They are very thin. There is also a joint that divides the room into two halves (roughly into two 3.5 x 3 meter sections).
And if you stand with one foot on one section of the screed and the second foot on the other part of the joint, and switch from one foot to the other in some places, there is a creaking sound. In some places you can see how different parts of the screed, separated by the seam, slightly shift against each other – probably there are joints over the entire depth. Some of the joints are completely silent and visually immobile.
What could be the cause of the squeaking? Does the screed rub against the screed in the joint area?
If you widen the joints in the area of interior doors to ~ 4 mm, that should help? After widening the joints, sealing them with sealant.
A doubtful plan, in my opinion. It may stop squeaking, but there will still be shear.
Alternatively, lay a couple of layers of GFB on top, so that the floor evenly distributes the load on the screed (i.e. to remove the possibility of shear between the boards)