I'm planning on using Mapei Ultraplan 3240 self levelling compound to level my living room floor prior to having 9mm Laminate flooring laid. The subfloor consists of original floorboards with hardboard sheets on top and then plywood sheets on top of the hardboard. Some of the plywood has been taken up around the edges in order to re-position a radiator. The floor dips towards the middle of the room and generally it is uneven. I have a builder who thinks he can level the floor quite easily. His plan is to prime the subfloor with PVA, lay a light black fabric over the floor and up the bottom of the walls (I'm not totally sure what this is) and then pour the self levelling compound over this. I think he wants to mix the self levelling compound so it is not quite as runny so he has a little more control over it. I'm just wondering if anyone can offer any advice on if this will work and if this method seems okay? I'm concerned that the PVA is not the correct primer to use, whether or not this fabric will stop the SLC from adhering to the floor properly and also I'm not sure if we need to leave an expansion gap by adding some foam to the bottom edges of the walls. Photo of the floor and fabric attached.