2 rooms have been knocked into one but the extra room's floor is slightly higher 1.5" than the other can this be levelled by sand and cement screed or will the whole floor need re-laying if the screed is ok it will raise the kitchen floor and create a step into the kitchen from the hallway would the screed be strong enough to allow this and allow tiling on top afterwards or would the screed need supporting at the step edge? any help greatly appreciated thanks