Moisture in concrete sub-floor following leak

Timeline/summary of events over the past 3 months:

Large water leak from upstairs cistern on 18th June (I calculated 2,500 gallons over 6 hours, but much of it would have been diverted via the cistern overflow pipe). I'm insured via Saga, with Acromas being underwriter for the buildings insurance. They have subcontracted Davies Co. as loss adjuster, who in turn have subcontracted Midlands Response (drying company), Blyth Group (builders), Bishops (removals company) and Aspect Contracts (asbestos company).

Midlands Response removed the sodden kitchen ceiling from my kitchen floor, removed all carpet and installed two large dehumidifiers (one upstairs and one downstairs) for 5 weeks, after which they (apparently) issued a drying certificate to Davies Group (loss adjusters). This took things up to end of July.

19th August, removal company took my furniture and put it into storage, so that on 20th August, Aspect Contractors could remove all the asbestos-containing thermoplastic tiles. They left the bitumen glue on the floor (apparently, this is often ground off before laying screed), and applied PVA to seal the bitumen, which also contains small amounts of asbestos.

The following week, I got high moisture readings (90% plus) in several places on the concrete flooring, from a hygrohood I borrowed from a local flooring company.

Midlands Response were therefore called back in week beginning 9th August and obtained readings as high as 99% RH (in the understairs cupboard) and of 90% plus elsewhere. They installed two dehumidifiers (one condensing type and the other a dessicant type), and put down two hygrohoods. Dehumidifiers were kept running 24hrs per day for a week.

Today they came back and found readings of 86% RH and 89% RH from the two hygrohoods. They also took some readings in the kitchen area, that still has ceramic tiles down (the kitchen/diner had carpet on the dining area, and ceramic tiles on the kitchen area, but the loss adjusters said there was no need to lift the ceramic tiles), and found high readings there too, indicating the water may have migrated under the ceramic tiles (maybe via the grout/adhesive?).

So ... the dehumidifers will stay where they are for another 10 days or more. They have drilled holes and installed two floor plug hygrometers, to get readings from further down in the concrete. The technician commented that the concrete was pretty soft.

That's the background/timeline, but I am very wary of rushing things in case I regret it. So, my questions are as follows:

Does anyone more knowledgeable than I am know whether the softness in the concrete sub-floor is possible due solely to 3 months of being wet from the leak event, or would this be a sign of more long-term damp/a more long-term problem?

Blyth Contractors' schedule of works listed (a) Apply self levelling compound and (b) Install bitumous DPM 2 coats. If the concrete isn't fully dried out, won't the top-coat DPM just create a moisture sandwich (with the original DPM below the concrete base), causing the moisture to find its way to the internal walls, and creep up there?

 

Thanks for your advice. Midlands Response were also using another measure (grams moisture per kilogram of concrete, maybe?) that was too high (way over 15g/kg, which they said was the acceptable level to add flooring without a DPM). I don't know what happens next if they come back and find the levels are still too high.

 

You could do with getting someone to grind the adhesive off as they will help it dry.

 

When was the house built?

 

Sorry, missed your post as I have been away. The house was built in 1963, I believe.

As far as I know, there's a DPM under the concrete, mainly based on (a) knowledge from local flooring company of several houses in the neighbourhood that had the Marley tiles removed over the years, followed by new flooring (laminate, vinyl, the lot), with no subsequent damp issues, (b) also, the bitumen looks like it was used as adhesive only, not as a DPM (is only a very thin layer, with the swirls you see from an adhesive spreader).

 

I just wanted to post an update, in case it is helpful.

After several weeks, the drying company sub-contracted by Davies (loss adjusters) got dry readings. Just this week, a company that specialises in commercial flooring (e.g., shops, warehouses, etc.) completed the job. Uzin 196 self-levelling compound was used in conjunction with Ardex MVS 95 DPM. I chose Karndean looselay vinyl as this is rated for higher levels of moisture content.

Prio to this, I removed all skirting boards and except for an area by the front door, no signs of rising damp (i.e., no wood deterioration or wallpaper peeling off).

Hopefully, will have no further problems and can get on with living in the house instead of the conservatory! Thanks to those who responded.

 

Did they stick the 'loose' lay?

 

I believe they used Tackifier.

 

Make sure the Insurance company also compensates you for running the dehumidifiers for such long periods. They eat electricity up!! We was given an extra £100 for this by our insurance company, using only 1 for approx 8 days.

 

Thank you - they actually did reimburse me, for (a) 2 condensing dehumidifiers and 2 big fans for about 28 days, and then (b) 1 condensing dehumidifier and 1 desiccant dehumidifier for 35 days (running 24hrs/day). So overall, 126 days of dehumidifier use plus 56 days of fan use.

I think in total I received over £500 for electricity, which more than paid for the electricity actually used. I presume they calculated using a standard fuel tariff, whereas I am on a cheap tariff.

 

Let’s hope you have a good water table as that’s the wrong dpm used. Based on a screed done in 1963 I’d say 95% there won’t be a effective damp proof membrane under it so a epoxy dpm should of been used like Ardex DPM1c.

 

Yes, that's exactly what they were originally going to use, if I recall correctly, but for some reason they changed it to the Ardex MVS 95 DPM.

I do think the original DPM below the concrete slab had been compromised by the services being run through the floor (meters are in the very middle of the house, in the understairs cupboard). The skirting boards and plaster around the corner of the cupboard showed some signs of rising damp, but I'm being optimistic and hoping that after 56 years, if that's all there was, and with the new DPM on top, there'll be no further problems and it will outlast me (I'm in my 60s).

 

Dang, I wish you hadn't told me that, as it's worrying me. Could I ask you why it is more likely to fail (in the least technical terminology, if possible)?

The floor has been laid, with Karndean Looselay on top, and the other reinstatement work is now being done (redecoration, new kitchen, etc.).

 

At least you have Karndean looselay. It might be alright


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Not much you can do now. I’d be keeping your invoice and asking what warranty you have off the floorlayers.

MVS is for Residual Moisture only so new sand and cement screeds. Did they grind the old adhesive off the sub floor or put the mvs straight to it.

 

Thank you for explaining. They did not grind off the old bitumen adhesive, but put the MVS straight onto it.

The whole estate has the same concrete slab construction, with DPM below, and thermoplastic tiles on bitumen adhesive (originally, at least). From conversations with many of the residents they have all at some point removed the thermoplastic tiles (but not usually the adhesive), and laid vinyl, laminate, etc. The local flooring company also told me that he (and his father before him; family business) hasn't ever seen problems subsequently.

I'm keeping my fingers crossed that having gone beyond what my neighbours have done, and using Looselay, things will work out OK.

I will get hold of the invoice, though. It only struck me that I hadn't received it when you mentioned (all I have is the quote).

 

Thanks, kick me while I'm down why don't you?