Rising damp coming through chipboard on concrete floor

[nags]

I had no idea there was a problem until we had new carpets laid.
The fitters alerted me to ugly black mold strains on the chipboard floor, mainly in one alcoved corner.
The black mold seems to be mainly spreading out from where there are screws, which have gone rusty, and also on one edge next to the outside wall.
My moisture meter says the chipboard floor is 20% around the screws, otherwise 10%
I have taken up a section to invest.
There is a concrete floor with wooden battens about 1.5" deep, and polystyrene sheets in between the battens.
I found really black mold on the underside of the chipboard in places, in one place with brown veins running through it where it was sitting on top of the polystyrene.
I have a moisture meter which says 40% in the concrete, skirting 15%, wall plaster 20%, battens 15% rising to 20-25% near the screws.
The chipboard surface is 10% except near the screws its 20%
I suspect the screws used to screw down the battens have penetrated the dpc.

The house is built on a slope, and the alcoved part is essentially underground.
The walls feel dry (altough reading 20% moisture) and decoration is unaffected.
I would really like some advice!

 

[KenGMac]

nags, good evening.

Notice this is your first post, welcome to the board.

First question? is do you have a Combi Central heating system? if so are you having to Re-pressurise the system on a regular basis? if you are Re-Pressurising the system then there is a leak in your Central heating pipework under the floor.

Was the property constructed by a Local Authority? I [unfortunately] have encountered several such shall I call it events, where ground water or sewage has flooded into the property

Other Questions?
1/. Is there a local history of such events in the estate?
2/. Have you or a neighbour had or are experiencing underground drainage issues?
3/. Any other rooms affected?
4/. Have you noticed an increase in Condensation in the house, on for examples windows first thing in the morning??
5/. Is there any water ponding outside / around the house?
6/. Have you seen any drainage related activity anywhere your house, something like the local water authority lifting man hole covers Etc.

Lets see what the board comes up with on this?

Do you have House Insurance? if so you can consider telling them you have a leak?? [In Insurance speek] an Escape of water from a fixed domestic installation [or drain leak?]

Suggest at present you do not contact your insurer until the board responds, and some answers to the above will assist.

Ken

 

[endecotp]

I have a moisture meter which says 40% in the concrete, skirting 15%, wall plaster 20%, battens 15% rising to 20-25% near the screws.
The chipboard surface is 10% except near the screws its 20%

Unless your meter is designed for concrete, it is probably only giving useful numbers in wood.

I also wonder if the screws directly affect the readings, i.e. they are metal and so conduct electricity and that it what it is measuring.

You need to compare meter reasings like-with-like, i.e. compare the chipboard with chipboard in another room, concrete with concrete in another room, etc.

(You obviously have (or had) a problem - trust your eyes as much or more than the meter!)

 

[nags]

KenGMac, thanks for your comments, yes we do have a combi boiler, and it does need re-pressuring now and again, but there's nothing to suggest the pipes run under the concrete at this point.
The house wasn't built by the local authority, this room and 2 others were built on as an extension, I would guess about 30-40 years ago.
1/. Is there a local history of such events in the estate? NOT KNOWN
2/. Have you or a neighbour had or are experiencing underground drainage issues? NOT KNOWN
3/. Any other rooms affected? NO
4/. Have you noticed an increase in Condensation in the house, on for examples windows first thing in the morning?? NO
5/. Is there any water ponding outside / around the house? NO
6/. Have you seen any drainage related activity anywhere your house, something like the local water authority lifting man hole covers Etc. NO
Of course, we do have insurance.
Endecopt, thanks also.
I did check the reading on other concrete (my garage floor), and it says 20%, so I reckon 40% is a good indication of excess moisture.
The chipboard, I'm comparing the region around the screws and along the edge where its black (20%), with the rest of the chipboard, where it is 10%
I cant see how the metal screws could affect the reading.
The wooden battens do feel damp.
However, I did remove one of the long screws that holds the batten to the floor, and although it was rusty at the top where it had been in the wooden batten, it was not rusty below that, which suggests water isnt wicking up through the screws. They go 4cm into the concrete.


Read more: https://www.diynot.com/diy/threads/...board-on-concrete-floor.500265/#ixzz5B1bI2ue6

 

[TicTac]

You've either got a straight forward " lack of dpc" problem, or this floor is where the CH is leaking, so you first need to work out which. Do the high readings come from a particular area that would suggest a pipe, or are they random, and that would suggest lack of dpc.

You need to lift everything and investigate further, then come back with the results.

 

[KenGMac]

OK moisture meters back in the day were not all that complex, you were advised by the manufacturer to revert all readings back to WME [Wood moisture Equivalent]
Modern [expensive] gismos can be used on various substrates, flick the switch and of you go.

Given the readings appear elevated in the affected area, there are two [obvious] possible causation's.
1/. An internal water leak, your requirement to top up the C/Heating on a "Regular" basis is food for thought??
2/. An external source, such as high ground water table. a leaking drain [storm or sewer] -- hence the question about external ponding water? --

If the area of the extension is lower than the original property it could be that if you have a C/H Leak the escaping water could be ponding in this specific area??

Are there, as far as you know any water feed or C/Heating pipes in the area? even a couple of meters distant ? or even a drain?

The rational behind the question about insurance? was that you can consider making an Insurance claim, there is obviously implications, higher premiums going forward, but the insurer should instigate investigations, at there cost !!!

Ken

 

[nags]

Yes, the extension is lower than the house, and the area affected is in the most underground part.
Yes, there is a drain close by, but the wall on that side seems dry.
I had reputed local builders in, who drilled an inspection hole.
They were of the opinion that the battens were added as an afterthought following swelling, and that the screws have gone through the dpc, but that's all turned out to be wrong.
Their solution is to "tank" the area and relay the floor for £2500+VAT
And also, yes there are water pipes in the vicinity (I think).
I'm considering blocking the pipes off to see if that reduces moisture.
The other evidence is the very bad mold on the underside of the chipboard at one point near the wall.
I will remove the skirting along that wall for a better view of where the dpc laps up the wall.

 

[Mr Chibs]

If said floor is lower than the outside ground, could bridging (getting above the dpc) be a suspect from the outside?
I had a similar problem until I removed the floors, one had a DPM layer, one didn't, but both were too high and causing damp patches here there and everywhere.
Mind you it looks very wet.

What are the floors like either side of the walls (where, internal) of your photos?

 

[nags]

The walls seem dry actually

 

[Mr Chibs]

What about the floors?

 

[nags]

Mr Chibs, please read original post

 

[KenGMac]

OK.

It appears that there are 2 general sources, external or internal??

A/. External high or rising water table. [not covered under any Insurance Policy]
B/. External underground sewer / drain or water feed pipe. [What is known as an insured peril under your Insurance Policy] -- Covered under the Policy---
C/. Internal Escape of Water from either the Central heating or domestic hot or cold system. [Known as an EOW from a fixed domestic system]

Given the area being affected is a low spot any of the above can /could be the causation???

You could consider a process of elimination, have a CCTV survey of the nearest underground drains / sewers? Have a pressure test undertaken on the internal C/Heating and Hot and Cold systems? I recall you did mention the Combi needed to be re=pressurised???

Why my references to what is and is not an insured event?? You could try an Insurance Claim??

As for ground water? there are tests that can be undertaken to see what the source is, either Fecal or containing Chlorine? but the test aint cheap and if it is undertaken by the water board, they will state it contains Fecal material, if tested by the local drainage authority they will say it contains Chlorine, such tests need to be undertaken by a reputable independent test house.

Your call but??? do you opt for tanking or do you instruct testing, or do you make an Insurance Claim??

Ken.

 

[Adsy83]

Have you lifted the cupboard?

You said the house is on a slope... Is this room at bottom or top of the slope?

And what is the age of the house.

Do you have some photos of the area outside of the damp areas. How high is the ground level

If the ground level is high outside then dpc is a waste of time. That stops upward movement not horizontal ingress.

If the ground level is too high you have 2 options... Reduce the ground level or tanking.

 

[nags]

Thanks for all your responses.
To answer a few questions:
The house was built in 1965 and the extension at the rear, of which this is part, in or around 1975.
The extension is at a lower lever than the front of the house.
At the area affected it's about 3-4 ft below ground.

Although there are black mold marks in the central ares around the screw holes, the worst appears to be around the edge, on the outside wall side.
And of this, one particular area is worst than most (this is picture 1 above, with the veins in it).
Carefully checking the walls with my damp meter, mostly I get 10% on the outside wall, but rising to 15% around the area worst affected.
So, then checking outside, there are steps leading down from upper to lower level, with no dpc between them and the wall of the house.
Therefore, I have cut away the edge of the steps by about 9" to eliminate this possible source of water ingress.
This doesn't explain how water has seeped across the cavity, but the moisture reading in the concrete has fallen from 40% to 25%, though this might just be because we've had no rain lately.
I intend the remove the skirting next to look for more evidence, and I have noticed a finger sized hole in the floor dpc, above floor level, where it is lapped into the wall. I can feel fresh air coming through this hole...

 

[Adsy83]

Damp meters are really a waste of time.

The problem here really does sound like a ground level problem.

I do think you need to either lower the ground or tank.

The problem with tanking however is that over time your bricks can crumble as the moisture is just left there.

External ground levels need to be 200mm below floor level.

Without more photos I wouldn't know for definate but installing French drains around the property may hell. These are shallow gravel filled trenches that aid evaporation