Level and damp proof bedroom floors

[Ramdalf]

I’ve recently had contractors in to remove the (asbestos containing) Artex ceilings in my bungalow, as well as Asbestos tiling that was covering the floors in the bedrooms. It’s the latter that I’m now considering doing follow-up work on.

Having lifted the tiles, it appears that they were glued down using bitumen. I had this tested for Asbestos (in a different area of the property) and this came back negative, so I’m assuming that’s the case all the way through. I also understand that this bitumen would have acted as a rudimentary DPM.

My issues now are two fold. Firstly, there are now holes in the bitumen, both from where some bright spark had nailed gripper rod into the Asbestos tiles and concrete beneath, as well as the odd hole that looks like may have been historic wiring:

You can also see that the bitumen doesn’t run right to the edges. I’m a bit concerned that these may compromise the surface, and I’m not sure if the concrete beneath has a proper DPM below this. I’m doubly concerned because my property is in an area that’s at moderate risk of groundwater flooding.

At the same time, the floors are not level. So I’m considering the best option for fixing the floors - I may be worrying about nothing, but I’d like to get things done right once, and not have to worry about them again, and would like to get back to level floors that will be water resistant.

From my reading online, it looks like one option may be an Ardex DPM sandwich - a layer of their SLC (which I understand binds ok to Bitumen), a DPM then another SLC layer. Does anyone have any experience with this in situations like mine, or have any other suggestions?

Also, this is a basic question, but what trade would this work fall under? Would this just be a regular builder, or would a specialist be more appropriate?

 

[jeds]

I think your best bet is to establish 100% if there is a potential dampness issue before you start solving one you don't know you've got? Tape a sheet of poly over the floor - about 2m square...ish. In a week or so, if there is any condensation beneath the poly, you might have some dampness in the floor slab. If not, given the weather at the mo, you can be fairly sure the slab is dry.

 

[Ramdalf]

Thanks for the advice - that’s a good idea. I did have a pool outside one of the bedrooms yesterday thanks to some dodgy guttering, so it certainly is a good stress test!

I guess the other aspect though is the groundwater flooding risk, which I guess it’s difficult to know whether I’m vulnerable to until if and when it happens. i guess I’m of the mind I’d rather be sure and not get a nasty surprise down the line, but equally I could just be being paranoid.

 

[jeds]

A surface dpm is really to protect finishes from vapour damage rather than keep free water out. If water pressure gets that far a few nail holes in the membrane is the least of your worry.

 

[Ramdalf]

Just a quick update on this - @jeds i tried your idea, but added to it by placing two Bluetooth temperature and humidity sensors as well - one underneath the covering, and one on top:



Whilst there’s no visible condensation on the sheet, in the part of the room pictured above (that has obvious holes), there was a difference of about 40% humidity - around 50% on top of the sheet, and 90% under it. I then moved the sheet to another area in the same room, and that had about a 20% difference - about 70% under the sheet.

I‘m going to move the sheet to the modern extension area and repeat the experiment as a sanity check, but if the humidity is similar for both sensors there, then that would seem to indicate that water vapour is indeed coming up through the floor?