i think the best way to tackle this floor without raising your floor height.imo take up the exhisting timber floor boards and chipboard. strenghten floor joists where needed re do with 25mm marine ply but where it meets the concrete chisel the concrete where it protrudes into the plywood area so the ply sits flush with the concrete(if you get wat i mean) you will have to screw and plug the ply to the concrete.then you will be able to create a clean joint along the length of the room you will only have to install one movement joint..hope this helps.. i wouldnt attempt to put an uncoupling membrane over this substrate..
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