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?
Honestly remove everything and start from scratch, if it’s generally quite uneven it’s always going to be a nightmare to level properly then go the Ardex route. Sent from my iPhone using Tapatalk
Thanks for the reply. By remove everything, do you mean remove the bitumen coating, or the entire subfloor? The latter I think is likely to be cost-prohibitive for me.
What kind of damp meter did the builder use? Was it a pin probe type? ( If so then that's not the correct one to use on concrete) mainly used for wood, timber and sheet materials. Grind the bitumen off, take a proper reading then use adequate dpm and compound (don't mix manufacturer) Also I very much doubt that your floor has a mechanical dpm sheet and if it does it has probably failed by now.
You can look at tilemaster for a chrome alternative to Ardex. They have similar systems that will level and damp proof that floor
It was the pin probe type, yes. Good to know that’s not the right one! For what it’s worth, I did a crude experiment where I stuck two cheap temp and humidity sensors next to each other, one under plastic sheet glued to the floor, and another on top. The one under the sheet had about a 40% higher humidity value (90% or so) than the one on top in the area that was yellow. The green area still had a difference of about 25% (about 75% under the sheet). I did the same test in the kitchen which is a new extension, and on top of the old parquet floor in the living room, and there was zero difference in humidity in those areas.
