Hi, I’m new to the forums, and am looking for some advice regarding levelling and DPM installation in a bedroom of my property, which is an early-mid 60s bungalow, with concrete subfloor topped with bitumen adhesive (was holding down Asbestos containing tiles that I’ve had removed): I’ve had a builder out to quote for the levelling and damp-proofing. The damp levels in the current floor are borderline; some areas showed green on the builders damp meter, and others yellow. I’d prefer to err on the side of caution, and get a fresh DPM laid so I don’t have to worry about it again. The builder has quoted for applying 2 coats of Everbuild Black Jack, followed by a layer of Arditex NA. I have a couple of concerns about this however. Firstly, I‘m not sure if it’s a good idea to mix products from different brands. My understanding was the recommended approach in my situation is the “Ardex Sandwich” with a thin layer of Arditex NA, their DPM 1C, then another layer of NA. My other concern is I believe there are significant drops across the floor, potentially to a total of around 4cm from the highest point. I don’t have the tools to measure properly, but there’s certainly a drop of 2cm beneath the original skirting board at one end of the room that seemed to roughly match what my spirit level told me: I spoke to an Ardex rep, and he pretty much confirmed what I thought - they said don’t do what the builder said, use their “sandwich” method of NA / DPM / NA, and confirmed what the data sheet says of a depth of 3-6mm for each layer (due to being on top of bitumen and DPM 1C respectively). When I raised my concerns around the fact that the first layer is going to pool in the low points and will inevitably be a greater depth than this, he suggested chipping the bitumen in the affected areas, to allow for the full depth of NA to be used. However, I believe the floor is generally not level, rather than it being in a single corner of the floor, so this approach sounds quite costly, as presumably at that point I might as well get the bitumen ground off, which I’d also rather not do - I have had the bitumen tested in another area of the property for Asbestos and it came back negative, but that doesn’t mean that this doesn’t contain it. Obviously the ideal would be to rip out the entire screed and start again, but my budget does not allow for that. Does anyone have any recommended suggestions on how to proceed?