What does abrasion class mean?
Opinions differ on this subject. It is often assumed that screed that was installed years ago will have dried out over time. This can certainly be the case. However, to receive the full manufacturer’s warranty for your laminate floor, you should exclude all possible sources of damage. So when laying laminate, also think about a vapour barrier film – that way you are on the safe side and won't be annoyed later about ripples in the laminate flooring due to moisture or about the warranty being voided.

Further information about vapour retarders can be found on the following page: Why a vapour barrier?
Selection of vapour barrier films and accessories
Further questions on the subject
We want to lay laminate flooring on wooden floorboards. Which underlay do we use? Why a vapour barrier?We have chosen an insulating underlay that is already equipped with an aluminium foil as a vapour barrier. Is the underlay laid with the silver layer facing upwards or downwards?How do I reduce the walking noise of laminate flooring? How much wall gap should I keep when laying?Which is the best insulating underlay to use with underfloor heating?When do I need a vapour barrier film?