Concrete Floor Causing Damp

The wall dividing my kitchen and extension is damp. It's the only wall in the house that has a concrete floor either side of it and the only one with significant dampness (even though it's been dpc'ed and lime plastered - no guarantee, done by a plasterer).
My initial feeling is to remove a couple of inches of the concrete floor next to the wall and install some membrane but I have no idea whether this is feasible or whether it's just a daft idea.
Can anyone help? I'm 95% sure that the concrete floors are drawing dampness to the wall.
Thanks, Ed.
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     snipped-for-privacy@googlemail.com writes:

What method have you used to determine this?

What form of DPC?

Lime plaster isn't any proof against damp, although it's not harmed by damp like gypsom plaster is. You would need a sand/cement/waterproofer scratch coat to resist damp coming through to the surface.

What pipework do you have in or above the wall? What's on the top of the wall?

I can't think how. Only mechanism I can imagine is if concrete floors are below water level with the wall penetrating them. How recent are the concrete floors, and do you know if they have a DPC? Are they damp?
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Andrew Gabriel
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snipped-for-privacy@googlemail.com wrote:

Warm air always seems to make a beeline for the coldest and lowest part of the house. Stand a tile or a piece of glass against the wall. If it gets wet, you know it's condensation. Insulation is the answer
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I'm sure there's some merit to that, it's just that the walls are noticeably damper after rainfall. Granted, the extension and kitchen (the wall adjoins these) have no radiators.
However, the damp is at the bottom of the wall, going up about 3 feet.
At the top of the wall is the felt roof of the extension but it's not damp at the top of wall.
There's a paving slab on top of some concrete, which formed a base for the boiler I've just had replaced (and moved to another location). It might have been leaking. It is possible I suppose. Another possibilty is that the paving slab/concrete was bridging the damp proof course. However, on the same side of the wall, past the door frame, it's also a little damp.
This is why I think the concrete floors may be the problem.
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snipped-for-privacy@googlemail.com wrote:

I wonder if that would be the case after summer rainfall. At the moment it's difficult to separate wet from cold. With concrete and no heating it's difficult to see how you can avoid condensation, and IME it does tend to collect on the lower half of the wall.
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Thanks Stuart but condensation explain the bricks in one patch being wet through, which was noticed when the plasterer was doing the remedial work? The plaster on the outside was wet but it seemed more like water going out and then water condensing from the outside going in?
Would a radiator in that room help rather than cause more condensation?
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snipped-for-privacy@googlemail.com wrote:

A rad should reduce condensation, if that's what it is. If not, water is either coming through the wall, or up through the floor into the wall. Obviously if this "wet through" patch isn't at floor level it might suggest the former. You can normally tell from the condition of the outside wall whether it's leaking. Is it rendered/painted or what?
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There is render on the outside of the wall and that has "blown". Quite a tapping sound. I'm not keen on render after a plasterer told me it doesn't let the brickwork breathe.
I should also point out that after rainfall, the garage floor is often wet through. I live on a hill and think that drainage is a problem...
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Then you probably have penetrating damp. Hack off the blown render, pva the brickwork, and re-render. The pva doesn't act as a waterproofer, it allows the render to dry properly without the water being sucked out of it by the brickwork.
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On Dec 15, 4:29pm, snipped-for-privacy@googlemail.com wrote:

Knowing nothing about 'rising damp', which seems to be UK terminology, respectfully suggest that if it is not dampness infiltrating from somewhere else (outside ) etc. it may be condensation on cool surfaces? In this climate, this year, the whole year has been wet and cool. More recently it has been very damp and wet. We have had twice as much rain, in this part of eastern Canada, already to Dec.14th as normally the whole month of December, and then some! Consequently some homeowners are seeing condensation droplets in places on unfinished uninsulated concrete in ground basement walls. Especially where air circulation is low. We also hear occasionally about 'dampness' in poorly ventilated closets (stand alone wardrobe cupboards are rarely used here) in this type of weather especially if located on outer walls of the house. Shortly it WILL be winter and we will be heating somewhat continuously; house air will be dryer and many of the dampness problems will go away. Just a suggestion anyway!
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snipped-for-privacy@googlemail.com wrote:

yes, but does it need to?
Its a perennial quetion.
What is damp? Damp is more moisture coming in than is going out.
What should I do about it? stop it coming in, or help it get out. Or both.
Opnions are divided between the big endians and the little endians. The big endians want no DPC, and all natural materials with a howliing gale and walls like sponges to 'let it all out'. People in this camp are greenpissers mainly.
The little endians want to stop ingress and use the minimum amount of heat and ventilation to cope with the irreducible residue. They are seldom treehuggers, but their solutions use less energy to keep warm and dry.
the worst thing you can do of course, is half and half. Stop it getting out, thinking you are stopping it getting in. Then the greenpissers shake their heads and mumble into their beards that 'the old ways are the best, you should've used lime mortar' and the usual bollocks.
My guess is that that blown render is allowing water behind, and not letting it out again.
and whats behind it is as full of cracked mortar as a swiss cheese is holes.
rip it off next spring, and post pictures. But if its ugly, i'd patch the pointing and re-render.
that will slow the ingress down to a level where the interior heating and ventilation can cope.

same here.
I don't totally discount rising damp as well, but that 3ft UP the wall is a bit too high for it to be the cause.
Was that wall ever injected at all? If so, it should stop the rise as it were. Unless the wall is full of rubble that its bridging it.
That's easy though. Knock a few bricks out and pull out the crap.
Look. short of getting an INDEPENDENT report from e.g. a firm of structural engineers, which may be worthwhile, I'd be tempted as a first attack to open up the cavity if there is one, and see whats inside, and take it out.
That will almost certainly reduce the height of the damp. Also, if, when it rains, water is trickling DOWN, you will know you have a problem higher up.
If it really is coming up, you probably want to get the wall injected and the concrete edges too, or chip back the screed to the DPM, and inject the wall below that, then tank up the inside with a strong waterproof mortar, or put a DPM up the lower few inches of the wall.
Then in better weather, investigate that blown mortar render, and sort it properly.
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i've dug a trench around my house, and when it rains I look at the levels and lower the bits where water stays, i will be asking for advice about French Drains soonish so I can return it to a flowerbed...
decades of gardeners had built up the garden higher than the air vents under the floors so water was getting under my floors thataway...
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snipped-for-privacy@googlemail.com wrote:

it sounds like the situation I had in my old house.
Utterly wet clay under the house, and various places where concrete or brick was sucking it all up. Much worse after rain.
one really damp patch was where the interior spine wall, which had been exterior, had concrete either side, just like yours. it was not the concrete, it was the spine wall itself. It had not been injected because it wasn't by then an external wall. and it would have needed to be injected below the DPM of the concrete, which was a practical impossibility.
the other damp path was another internal wall, but this one had back to back chimneys, one side of which had a suspended floor. the chinemys were simply too deep for injection to work, and when we lifted teh suspended floor, there was a small lake under it after rain.
the cost of underpinning these internal walls and chimneys with DPC stuff, plus the fact that most of the timber above had gone rotten, was the reason why the whole house was demolished, rather than refurbished. The refurb costs were looking already higher than rebuild. Just to cheer you up.
I suspect in your case that the wall itself is the problem.
unless it has a DPC of some sort below the concrete DPM, it will suck water up.
However there is a slight ray of hope. rising damp wont go up 3 ft. A foot or so is pretty much its limit. That suggests the wall itself may be getting wet some other way.
If its a cavity wall, and there is some sort of ingress near the top due to failed flashing or something..or mortar gone, the water will run down and accumulate in the cavity, and if thats filled with crap - and lots are - that will come out through the walls allright.
You say there is an extension: if its e.g a single storey flat roofed thing, look at the wall above the roof, and the flashing there. water bouncing off a flat roof can utterly soak a wall like that, and it doesn't take much - a lose bit of mortar - for the water to drive into the wall.
even if its got a pitched roof, the abutting of an extension roof to a wall is a potential weak point.
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Thanks a lot, NP. I suspect the roof has something to do with it, though I'd have expected to see more evidence of it at the top of the wall.
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Dear NP As an admirer of your posts and the content, it is with regret and a little trepidation that I have to disagree with your statement as to the height of rising dampness. In the several thousand houses I have personally visited as surveyor I have seen perhaps 500 odd with rising damp (figure subjective - but a substantial minority) and of these most had rising dampness to a greater height than 300mm I would estimate the average was double that at say 600mm. In many cases it was over a metre and I can remember a few some 3 or 4 I guess where it got to be nearer 1.25 Only a couple of weeks ago I was attending a technical forum of the PCA (what used to be the BWPDA) on which I serve and the subject came up. I quoted the normally accepted maximum of 1.5 m which is the BRE accepted maximum but one of the technical panel with whom I have worked or known for 30 plus years and who has much more expertise and experience of rising damp (I generally go for the decay!) than have I said that he had found it in one case just over 2 m high. As he was testing for salts and using appropriate BRE modus operandi (the then Digest 245 Test) I have no reason to doubt him. Chris
On the subject of this post - the wall and the floor - please could the original poster Bill provide data so I can perhaps help him? 1) is the floor a new isolated from the oversite with a membrane in a relatively recent structure or an old house where there is no membrane? 2) is the plaster in contact with the floor or is there a 1" or 2" gap as there should be 3) where is the dpc in the wall relative to the plaster and does the plaster bridge it? 4) what is the wall made of? 5)have any meter measurements been made and a contour plan of readings at say 300mm ccs be done to determine if there is a rising damp or condensation pattern? 6) has the same been done to the floor at varying times of year? Lastly a section of the wall and floor posted on the site would be useful Chris
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snipped-for-privacy@atics.co.uk wrote:

Well I bow to superior knowledge then.
I suppose its possible. but it USUALLY dries out faster than it can rise up, in my experience..at a few inches above wherever its enclosed..so generally you see efflorescence up to about a foot from floor level.

there you are bill, listen to the man. A free technical consultant.
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snipped-for-privacy@googlemail.com wrote:

Are both sides of the wall now internal?
Judging by what I've read so far in this thread, you have rising damp - it's highly unlikely to be condensation due to the fact that there has been a boiler against this wall for umpteen years. Penetrating damp can only get through if one side is prone to getting wet, and from what I can gather (although I may be wrong) both sides are now 'indoors'.
Water from above, IE a leaky roof or gutter is also ruled out due to the fact that it's damp only at the bottom of the wall.
Rising damp will go no higher than 1m...you said a plasterer DPC'd it for you? - how long ago and with what? - my guess is that he hasn't done it properly, or if he has and it was only recently, the DPC hasn't begun to start working yet due to the already high moisture content of the brickwork, wet brickwork can take years to dry out.
It's highly unlikely to be the concrete floor causing the damp
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Phil L
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