Part concrete floor - rising damp

[wuptdo]

Good Afternoon,

I got a pca-type surveyor in for damp/moisture diagnosis and a wall tie check, but taking the proposed solutions on the damp side with a pinch of salt. I’d like a few extra thoughts if possible please.

House background:
~1930’s semi, cavity wall construction, built with no DPC, ~50mm cavity, insulated with blown fibre. Insulation (from wall tie check) appears bone dry. In my personal opinion, if it’s useful to know, the house also potentially has externally applied (StormDry like) masonry cream. The house floor sits ~1m above ground level on all sides – aside from party wall. A previous owner has applied a (waste of time most likely) retrospective chemical dpc externally around the floor level of the house. The rear wall of the house is quite exposed.

The moisture/damp appears to be around the perimeter of the concrete floor. It is causing noticeable staining/damage to the side elevation. Going by what the damp surveyor has said and my own reading, I suspect the solid floor base material is wicking up moisture which is travelling through the concrete floor. It then hits the asphalt layer and is pushed sideways and comes up the plaster in the walls. Although, feel free to tell me that moisture is unlikely to be wicked up that far and the moisture is coming from elsewhere.

The damp surveyor has initially proposed extending the asphalt dpm with a plastic dpm part way up the walls and replastering. However I feel this may just mask the problem and the moisture still travels up the walls (potentialy wetting the CWI). I can think of two other possibilities that don’t just cover up the damp:
1-Remove the asphalt layer and allow the concrete to breathe naturally rather than pushing the moisture out into the walls. Or will it be far too wet? If I do this, how do I handle reflooring?
2-Dig up the floor and reconcrete with a plastic DPM? (use the occasion to insulate and install UFH)? How do you prevent the moisture travelling up the wall here/'lap into the DPC' (as there is no DPC in the walls)? Or can you retrospectively insert a plastic DPC / apply chemical DPC cream?

Thanks for any thoughts in advance!

 

[JohnD]

You say it's one metre above ground level. If you expose and ventilate the brickwork, water will evaporate off and will not climb a metre.

Is there a water leak under the floor?
(Yes)

You say it is a 1930's house. What country is it in that did not install DPCs 50 years after they became compulsory in England and Wales?

 

[wuptdo]

You say it's one metre above ground level. If you expose and ventilate the brickwork, water will evaporate off and will not climb a metre.

Is there a water leak under the floor?
(Yes)

You say it is a 1930's house. What country is it in that did not install DPCs 50 years after they became compulsory in England and Wales?

Thanks for the quick response.

Yep, I intend to expose that brickwork (relatively) soon - although it will have to wait a few weeks. I'm replacing and moving the 40 year old boiler that currently sits above the side elevation damp and I'm sincerely hoping that this may be a significant contributing factor. But the plumbers who have come to quote nor the damp surveyor seem to suggest it's related.

With regards to the country - England. (The no DPC is purely from my observations, I can't see any off-coloured brick / slate or otherwise below floor level externally - internally I haven't had a good look under the suspended floor just yet)

 

[JohnD]

Look at where the incoming water main rises through the floor, where the kitchen sink used to be, and the outdoor stopcock, where the garden gate used to be. Drawing a straight line between them, does it pass under the floor?

Can you turn outside stopcock on and off?

Have you got a water meter?

It is quite normal for a 90 year old water pipe to leak.

 

[wuptdo]

Look at where the incoming water main rises through the floor, where the kitchen sink used to be, and the outdoor stopcock, where the garden gate used to be. Drawing a straight line between them, does it pass under the floor?

Can you turn outside stopcock on and off?

Have you got a water meter?

It is quite normal for a 90 year old water pipe to leak.

Will do a run through a bit later re any obvious locations.

There is an internal and external stopcock but no water meter unfortunately to check for leaking over time.

 

[JohnD]

you can listen for a leak, I will explain tomorrow. do you have access to sharp young ears?

 

[wuptdo]

After utilising my caving expertise ... on the inner leaf is a visible dpc it seems. I can't see any evidence there is one on the outer leaf unless it's been well and truly pointed over.

Having inspected the concrete floor perimeter they have applied a chemical dpc internally it seems. I think the back wall where there isn't any major damp is like this because they have left a 2 inch gap between the floor and the start of the plaster (hidden by skirting). Where as the side elevation has the plaster all the way to the floor.

So I've spotted where the cold water feed comes in (after a wild gas line goose chase). This black (plastic? Maybe the house isn't as old as estimated?) pipe coming up through the floor it seems. Although the asphalt has been heavily disturbed.

Here's a photo to show the asphalt versus how it should look on my camera.

Thanks for all the help it's greatly appreciated. And keen ears? We have a pair - not mine!

 

[JohnD]

the black Alkathene water pipe was IIRC popular in the 1980s though there is no certainty of date. It was produced in imperial (inch) sizes. Sometime there is identification printed or moulded into the side. Modern pale blue water pipe indicates it has been tested as suitable for drinking water, and is produced in metric sizes. Lots of houses (including mine) have black water pipe.

Yours might have been a replacement pipe if the house is older, or it might have been a new bit added on the end of an old pipe.

the green corrosion on the copper pipe indicates damp or a leak. do the bricks look especially damp near the plumbing?

my first house was built in the 1930's and the steel water pipe in the concrete floor had been leaking for years and was replaced around 1980 with copper. the salt-glazed clay drains and gullies were also cracked and leaking when I moved in, and had been since 1942. this is usual.

sometimes you can get an idea of age by looking at the external stopcock connnections and the internal plumbing, for example the tap connectors and hot water cylinder, and the fusebox and cable.

If you turn the external stopcock fully off, then on, then fully off, and repeat, late at night when all is quiet, a young person with sharp ears, standing in the kitchen when no water is being used, toilets have not been recently flushed, can detect a leak by a faint hiss stopping and starting. the noise is so faint that you do not notice it, except when it stops and starts.

an engineers (mechanics) stethoscope costs a few pounds and can be pressed against a stopcock or pipe to help you hear it.

can you make out what the dpc is made of? slate was usual in 1930s

to my eye the black coating on the floor looks like modern synthaprufe or similar and may have been applied to hide (it does not cure) damp. it looks to me like the concrete floor has been dug up and patched.

 

[wuptdo]

I definitely know the house is pre-1947 due to a local photo I have seen. So I expect definitely a replacement pipe given what you've said - explaining the 'dug up' area. But considering the dug up area is rather limited in size, I can't imagine they replaced the whole thing.

The bricks back behind aren't wet at present - but clearly historic moisture has been here. Maybe due to drying out in summer? Or longer ago? As to the historic cause - not sure. It could have been moisture from the floor being soaked up and now the in-between plaster has been removed it's alleviated most of this. But as it's under the sink area I'd have expected a historic sink leak maybe. None of the current kitchen cupboards show any witness that the sink is leaking. Any current moisture above the plaster line could potentially be from condensation?

There is a pipe further around the room that is very green-blue/corroded but that sits directly on the floor in the small gap between the asphalt(or whatever it may be) and the wall.

The dpc looks and feels like tough leather/felt texture, maybe 2-3mm thick, definitely not slate.

Will try the water listening approach when I get the chance - thank you for this.

Thanks again for this.

 

[wuptdo]

Waiting on the stethoscope I've ordered at the minute. See image below re side elevation wall.

As a bit of damp limitation is there any harm hacking off 1-2 inches of the plaster at the bottom of the side elevation wall (as it's just providing a bridge to the damp concrete at the minute) past the asphalt floor - then covering with boxing/skirting later?

 

[JohnD]

hack off the plaster and it can at least start to dry by evaporation. don't cover it up. Look for the dpc when you take the plaster off. inspect the surface pipes in case they are the source.

that's quite a high damp patch you have

some people criticise me for suspecting leaking underground pipes making a concrete floor wet and soaking up the walls

but they do.

"rising damp" my asre.

one of the first places for an iron supply pipe to leak is the elbow where it turns up to come through the floor near the sink (due to cavitation corrosion on the bend). so maybe they just replaced the end bit. if the rest of it is still 70 years old it is entitled to leak. you can drill a hole in the floor and see if it fills up with clean water.

also look at the nearby gulley and drain for the sink, which probably got cracked in 1942 and has leaked ever since. this will be soapy or greasy water.

 

[JohnD]

The dpc looks and feels like tough leather/felt texture, maybe 2-3mm thick, definitely not slate.

like bituminous roofing felt?

 

[wuptdo]

like bituminous roofing felt?

...yes ? ... I haven't used too much roofing felt before though. it doesn't have the 'sandpaper' external texture I would associate with roofing felt though.

Used the stethoscope on the water inlet briefly, but couldn't hear anything distinct. Although I certainly wasn't that thorough just yet (I didn't involve external stopcocks).

Referring back to that side elevation wall with the damp staining that I pictured above. I haven't had time to hack the plaster off as of yet. I have been keeping an eye on that damp staining though, a few hours after consistent heavy rain there was 'new' (non staining) moisture a couple of inches even higher than the staining shows in that image (right up to the plastic ducting on the right more or less).

Had a look re sink drain. The bit I can see is plastic lined and looks in good condition and relatively modern. It currently goes through a raised patio (still 0.7m from the house floor). I guess it may be worth digging up the patio area to have a look at the main drainage.

 

[JohnD]

Used the stethoscope on the water inlet briefly, but couldn't hear anything distinct.

you need an assistant to turn the main stopcock on and off while you listen. the stop and start of the noise is noticeable, if there is a leak.

younger people have better hearing.

 

[JohnD]

a few hours after consistent heavy rain there was 'new' (non staining) moisture a couple of inches even higher than the staining shows in that image (right up to the plastic ducting on the right more or less).

aha!

can you show us a pic of the outside of that wall?