Laying new floor - needs DPM?

dunroving · 22 August 2019 at 11:27AM

Brief background: After buying a 1960s semi in south Birmingham house last year, and spending the summer managing (a) complete rewire; (b) installation of satellite and Ethernet wiring to all rooms; (c) plastering to make good chasing from (a) and (b); (d) redecoration throughout, I had a major water leak 2 months ago and so am looking at major works throughout the downstairs floor!

I've been looking at the cash settlement offer, as it allows me to take the opportunity to install a new kitchen. So, I may be posting one or two threads on separate issues, but didn't want to mash everything together.

Flooring: After ripping out the sodden carpet, it was found that the solid concrete floor was covered in Marley Tiles, which were tested and found to contain asbestos, meaning the renovation work couldn't continue until they were removed. The Marley tiles have now been completely removed. The schedule of works from the loss adjuster (provided by Blyth Group, contractor), says the following regarding the floor:

Apply self-levelling compound
Install bituminous DPM 2 coats

- I'm wondering why the DPM is needed. I've been told by one contractor that there should be a DPM below the concrete layer, so a DPM is unnecessary. However, I am wondering if that may be current practice, but that back in the 1960s, the idea was that the Marley tiles would serve as the DPM, on top of the concrete (or possibly that the bituminous glue underneath was the DPM).

Does anyone know whether my take is correct? The loss adjuster's contractor (Blyth Group) seem to know what they are doing, so if they suggest laying a DPM, it seems that's probably with good reason!

Thanks in advance. I haven't been on the forum for several months (since I was doing the renovations last summer), and really appreciate the great advice I get from here.

Doozergirl · 22 August 2019 at 11:44AM

What flooring is going over it?

My view is that if it ain't broke, don't fix it. You can cause issues that weren't there - like damp creeping up internal walls where there was no DPM before and the floor can't breathe anymore, so it uses the internal walls.

I would have though that a 1960s house would have a DPM. If you didn't have damp before then there is either one there and it's working, or there wasn't and the house was fine and breathing well.

dunroving · 22 August 2019 at 12:38PM

Hello again - and glad to see that you responded. Your help with recommending tradesmen last summer saved my bacon!

I agree with the "If it's not broke, don't fix it" principle, but as the insurers/loss adjusters/building contractor (* see below) insisted that the Marley tiles should come up because they contain asbestos and were crumbling, if that was originally serving as the DPM, it's already partway towards being "fixed" (i.e., has been altered).

So, if the bitumen and Marley tiles were preventing transfer of moisture, and they are now removed, there's a possibility that moisture from the ground (if concrete was laid directly on top of sand/subsoil, as apparently it often was back then) might now transfer up. The soil around Rednal is very, very high in clay (almost like Plasticine in places), so retains moisture.

When doing research earlier, I found several threads saying that DPM under concrete floors were not required until the mid-60s and so Marley tiles with a bituminous layer underneath was used as the DPM of the day. Couple of the threads were very reminiscent of my house:

https://www.diynot.com/diy/threads/concrete-floor-with-bitumen-paint-more-bitumen-or-seal.486497/

https://theflooringforum.com/threads/damaged-thermoplastic-tiles-and-cracked-concrete.14435/

Also, and interesting and amusing short thread here, about laying the wrong sort of flooring in these cases:

http://www.contractflooringjournal.co.uk/blog/asbestos-alert-bob-is-useless-and-dangerous/

(To answer your question, I'm currently thinking of getting good quality vinyl tiles/click flooring throughout the ground floor).

I don't suppose you would be interested in providing a quote for installing new kitchen, bathroom and toilet?

*(I have been project managing this whole insurance claim and so far have been talking with about 10 different companies! It's a good job I'm retired as I seem to have to stay home a couple of days per week, to wait for insurance inspectors, asbestos removers, etc. Having two different underwriters for buildings and contents insurance hasn't helped.)

FreeBear · 22 August 2019 at 3:17PM

dunroving wrote: »

(To answer your question, I'm currently thinking of getting good quality vinyl tiles/click flooring throughout the ground floor).

The only way to be certain that there is an existing DPM in/under the current concrete floor is to drill a test hole. However, this will puncture the DPM (if there is one) and need to be suitably repaired. Digging out the current floor and putting down a new one, whilst expensive and disruptive, would give you the opportunity to upgrade the insulation..

I used LVT click-loc tiles in my kitchen - Half concrete (with DPM) and half suspended timber - I still put down a large sheet of heavy guage polythene DPC followed by 5mm wood fibre underlay before fitting the tiles. The plastic will prevent any residual moisture tracking up through the flooring (LVT is waterproof anyway), and the bare concrete under the units will allow moisture to evaporate.

It up to you if you follow the recommendations of the loss adjuster. But I would use the self leveling compound, and apply a DPM (a plastic sheet that can be removed at a later date if problems arise) on areas that are to be covered. Leave bare, untreated concrete under any base units.

TELLIT01 · 22 August 2019 at 3:50PM

If the loss adjuster is recommending a bitumen DPM be laid, and it's being paid for on insurance, I really don't understand your concern. It won't have been recommended just for the fun of it. The loss adjuster / surveyor would have had a reason to include it. At the builder said "there should..." but a second DPM certainly won't do any harm.

dunroving · 22 August 2019 at 3:58PM

TELLIT01 wrote: »

If the loss adjuster is recommending a bitumen DPM be laid, and it's being paid for on insurance, I really don't understand your concern. It won't have been recommended just for the fun of it. The loss adjuster / surveyor would have had a reason to include it. At the builder said "there should..." but a second DPM certainly won't do any harm.

I don't think I said anything about providing a bitumen DPM.

If the work was all being done via the underwriter/loss adjuster/contractor, you are correct - the DPM will be installed.

My question arose because I am considering taking a cash settlement for some of the work. As part of looking into that, the first person who looked at the part I'm considering getting done myself (replace ceiling, redecorate, level floor, and install new kitchen) questioned why a DPM was necessary. From a purely MSE perspective, why pay for something that isn't necessary?

dunroving · 22 August 2019 at 6:15PM

Update:

I just had a local flooring expert come out to provide a quote for vinyl flooring. He knows the local area and houses very well, and is sure these houses have a DPM under the concrete. However, he said laying an additional DPM won't hurt, so being cautious, I'll likely go that route.

He also lays the screed so unlike the other flooring shop in the area, knows more than just carpet and vinyl.

Doozergirl · 23 August 2019 at 5:36AM

FreeBear wrote: »

The only way to be certain that there is an existing DPM in/under the current concrete floor is to drill a test hole. However, this will puncture the DPM (if there is one) and need to be suitably repaired. Digging out the current floor and putting down a new one, whilst expensive and disruptive, would give you the opportunity to upgrade the insulation..

I used LVT click-loc tiles in my kitchen - Half concrete (with DPM) and half suspended timber - I still put down a large sheet of heavy guage polythene DPC followed by 5mm wood fibre underlay before fitting the tiles. The plastic will prevent any residual moisture tracking up through the flooring (LVT is waterproof anyway), and the bare concrete under the units will allow moisture to evaporate.

It up to you if you follow the recommendations of the loss adjuster. But I would use the self leveling compound, and apply a DPM (a plastic sheet that can be removed at a later date if problems arise) on areas that are to be covered. Leave bare, untreated concrete under any base units.

This is what I would do, and have done in the past. It's removable.

If you're having something like an LVT then they'll probably want to put down a liquid DPM for their guarantee.

I'm not sure I agree when people say it won't hurt. I've seen the results of inappropriate damp proofing to properties that haven't had it previously and it's often, er, damp. That said, the house hasn't suffered so far with what was there, so that's positive.

Hit me up when you've decided on budgets and I'll see what I can do.

We start nearby shortly on something else, once the legals are finally sorted out.

dunroving · 23 August 2019 at 5:18PM

dunroving wrote: »

Update:

I just had a local flooring expert come out to provide a quote for vinyl flooring. He knows the local area and houses very well, and is sure these houses have a DPM under the concrete. However, he said laying an additional DPM won't hurt, so being cautious, I'll likely go that route.

He also lays the screed so unlike the other flooring shop in the area, knows more than just carpet and vinyl.

The plot thickens. The local floorist (not to be confused with a florist) loaned me his hygrometer for the weekend and so far the readings have been pretty stable at 89% ...

Doozergirl · 23 August 2019 at 8:09PM

Any idea what it's like next door?

I've got no idea if there could be retained moisture from the leak. It's not something I've experienced, but comparing it would be helpful, I guess.

markin · 23 August 2019 at 8:26PM

As said its the perfect time to upgrade the insulation at least in the living room, or to go with wet underfloor heating.

Laying new floor - needs DPM?

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