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Mysterious damp patches

(39 Posts)
tittysprinkles Mon 21-Dec-15 15:48:57

Another where's the damp coming from thread.

Background - 1930s semi purchased a couple of months ago. One small patch of damp on a back wall near a French window picked up on the survey thought to be due to failed DPC. Another couple of spots on the plastered over chimney breast in the loft thought due to leaking flashing.

All well and good, we are awaiting DPC treatment to rear wall of house near the damp spot (dubious benefit I know) and repair of flashing/repointing of chimney stack.

We are not living there yet as it is being refurbished so have had heating off most of the time. We have been stripping wallpaper, removing skirting and removing some damaged plaster.

This weekend we noticed a new patch of damp in the kitchen which is an extension built onto the side of the house. It is about 1/3 way up the wall above a radiator. Two new patches have appeared at the base of the same wall but about 4m away either side of an arch which leads to a small back porch. I assume the affected wall was previously the external wall of the house.

My question is, could the new patches just be due to condensation? It has been very damp weather and there has been a lot of condensation due to the wallpaper stripping.

We put the heating on and it is starting to dry out. Have had plumber in and no leaks. No obvious blocked downpipes or gutters and roof of extension looks OK.

Is it possible for condensation to cause this appearance and can we just ventilate and let it dry out or should we be looking for other sources of moisture?

tittysprinkles Mon 21-Dec-15 16:15:17

Here's the patches near the floor. No rust inside the plug socket.

fanofthevoid Mon 21-Dec-15 18:29:20

Message withdrawn at poster's request.

Raxacoricofallapatorius Mon 21-Dec-15 18:33:10

We had exactly the same problem. It was most definitely condensation.

HelloItsMeAgain Mon 21-Dec-15 19:24:45

You need PigletJohn to come along with his expertise. I think what he tends to recommend in situations like this is to tape a plastic bag over the area that gets damp - seal it on all 4 edges. Then look where the moisture is - if between the bag and the wall the moisture is coming into the room from above/outside. If it is on the outside of the bag it is condensation. Seems to make scientificy sense - and maybe worth a go.

OliviaBenson Mon 21-Dec-15 20:05:56

Are all the patches on chimney breasts? They look like they have been blocked up with no ventilation? If so, that could be a reason and you'll need to put a vent in.

PigletJohn Mon 21-Dec-15 21:06:41

is there a water meter?

tittysprinkles Mon 21-Dec-15 21:31:55

Thank you everyone.

No the patches in the kitchen are on what used to be the external wall of the house, the old kitchen would have been the other side. The room on the other side of the wall is now a dining room. The funny pattern makes me wonder if there used to be a window there which has been bricked up? Will have to ask the neighbours what their layout is like as they've not had a side extension.

There is no water meter.

PigletJohn Mon 21-Dec-15 22:55:20

is it a concrete floor?

PigletJohn Mon 21-Dec-15 22:56:51

is the extension full height, or is there a roof (esp flat) joining the wall above where wet patches have appeared?

tittysprinkles Tue 22-Dec-15 00:33:39

I think it is a concrete floor will check next time I'm there. It is not a full height extension, there is a pitched roof abutting the main part of the house. The extension has a very high ceiling though and no signs of damp at the top.

PigletJohn Tue 22-Dec-15 17:51:23

the pictures show local patches of damp, which makes me think of water from a leak. If it was condensation, I would wonder why that patch of wall is affected, for example is it a cold external wall or a chimneybreast? It looks like indoor wall. If it has recently been replastered and decorated, this may be to conceal damp.

If it is a concrete floor close to a kitchen or radiator, I would want to see if the floor is wet, because I would be thinking of a plumbing leak. There is not an obvious way for rainwater to get at those patches, and 80 years is a lifetime for a water pipe.

DPCs in 1930's houses are not likely to fail, but much more likely to be bridged by raising the ground level with flowerbeds, paths and patios. If this is the case, it should be remedied. Do not invite someone into your house who sells chemical injection, because he will tell you to buy chemical injection.

tittysprinkles Wed 23-Dec-15 11:50:27

Thank you. My brother is a plumber and has looked extensively for leaks (floorboards lifted, cutting open plasterboard to look at sealed off pipes etc) and nothing found. Boiler not losing pressure either.

The wall is internal but did used to be the side wall of the house before a kitchen extension was built. I've looked at next doors house (identical semi not extended to the side) and no sign that there used to be a window there.

Interestingly, we have had a joiner removing some woodwork around the windows (we are having a total refit) and has found that the cavity wall at the back of the house where damp was found on the original survey is full of debris. This is likely to be the cause of that patch of damp, rather than rising damp caused by failure of the DPC as advised by the "damp and timber specialist".

Damp treatment seems to be a bit of an industry with surveyors and builders in cahoots with each other. Might just watch and see what happens to the new patches for now!

Pigletjohn do you think rising damp actually exists?

PigletJohn Wed 23-Dec-15 13:22:37

I am prepared to believe that it can be caused, typically by bad building practice such as rubble in the cavity or putting plaster or render on a wall that reaches down to water and allows it to creep up, but I have seen photos of laboratory tests, and old buildings, of good clean brickwork, with no DPC, where the bottom of the wall is actually standing in water, but the damp only rises by a couple of courses. Ordinary bricks and mortar prevent water rising far by capillary action, because the tiny "pores" in bricks are smaller than those in mortar, and I am told by those who understand such things that capillary action will only allow it to rise across one join.

I have not seen a laboratory test of good clean brickwork standing in water where the damp does rise by more than a couple of courses.

Water can rise through walls saturated in certain chemicals, such as converted stables and cattle-sheds impregnated with urine salts.

Chemical treatment is often demanded by mortgage companies who like to think that something has been done, and by people who have been visited by chemical injection salesmen.

IME damp is usually caused by condensation (especially as a result of draping wet washing round the home, or throwing buckets of water at the walls, which amounts to the same thing) and by leaking pipes, especially those buried in concrete floors. It will also be caused by rainwater penetration, usually as a result of poor maintenance of gutters and render, occasionally by poor design. Chemical treatment has no effect on these defects.

Traditional UK construction has a wooden floor, and a void beneath ventilated by airbricks. The ventilation is usually enough for dampness from the soil to evaporate away from the exposed brickwork above the ground, and the water vapour to blow out.

Idiots like to block airbricks with concrete extensions and raise ground level with flowerbeds, paving and drives, enabling the groundwater to rise further up the walls before it can evaporate away. Dampness will stop at the level where water loss by evaporation exceeds water gain from the ground or other sources. For example my own house is built in soft bricks, on chalk, and the groundwater level can easily be seen, by the limescale, in the first brick up from the ground, but not the second, even though the DPC is above the second brick. See photo.

There are still people who claim that rising damp DOES exist. No doubt it would be wrong to suggest that they all are in the damp-treatment trade. There is a great deal of acrimonious argument.

See also

PigletJohn Wed 23-Dec-15 13:44:17


debris in cavity wall can be removed. Best way I know is to knock out a brick on the corner of the wall, and use a long narrow raker, and a powerful wet-and-dry vac which will suck out loose material. It is slow and tedious, but unskilled work. You can also reach down gaps exposed when a window is removed.

When I did it, my vac had a metal tube which was able to poke and loosen most debris and suck it out. Larger pieces were sucked onto the end of the tube and the tube had to be pulled back to remove them.

It's possible there are companies who do this sort of work for cavity-wall companies, but I have never seen one. A small builder in a quiet spell might put his labourer on it.

PigletJohn Wed 23-Dec-15 13:57:18


the two walls in your photos look short. I like the idea of making a hole into the cavity from the corner and cleaning out the cavity. That will interesting for you, and if the damp then stops, you will know what to do with the others. With the practice it will be easier.

tittysprinkles Wed 23-Dec-15 16:28:38

Yes I think that is what we'll do. Just wondering why the new damp near the floor in the kitchen would appear now if it was also due to debris in the wall cavity which presumably has been there for years? Could it be the wet weather, no heating on and condensation combined?

As an aside, the damp surveyor who is also a builder recommended installation of a complete new wall tie system as his endoscope revealed corrosion of the existing wall ties. Joiner can see them now in the cavity and says that even in the damp area they look fine...

I never thought damp could be so interesting!

JT05 Wed 23-Dec-15 16:54:25

Don't know if this is any help at all but, late MIL had a Victorian house and damp appeared on internal wall, half way up. This wall was next to the kitchen. The damp was a leak from a pipe buried into the wall at some time, to provide the kitchen with water. Just a thought.

tittysprinkles Fri 25-Dec-15 20:52:15

Thanks all. Am actually most annoyed about the wall ties.

The "specialist surveyor" was recommended by our estate agent so I assumed they were legitimate. An endoscope was used to look at them and rust was seen, and apparently properties of a similar age around the area have had wall tie failure too.

The replacement system would have involved drilling loads of holes in our brickwork, not removing the old ones but adding new ones at a cost of well over a thousand pounds. Which would have been totally unnecessary and affected the cosmetic appearance of the property.

My advice to anybody in a similar situation is:

The estate agent may recommend a particular specialist surveyor because they are quick to complete the survey and therefore speed up the purchase not because they are any good.

Get lots of quotes and recommendations by word of mouth from people who have used them. This company had lots of glowing internet reviews and was very convincing (member of lots of federations, associations etc).

If someone tries to sell you a replacement wall tie system ask them to pull out an old one and show you the state of it. For all the work recommended we were nearly ripped off to the tune of several thousand.

Merry Christmas!

PigletJohn Fri 25-Dec-15 21:08:18

lack of heating may have contributed, if it meant that water evaporated off the face of the wall slower than it soaked in.

Wet weather may have contributed, if the water table actually rose, I have heard of this happening but not seen it, usually on a hill where the ground is saturated, often from a stream, ditch or broken clay-pipe drain (have a good look at your rainwater gullies and tap any concrete round them to see if it sounds hollow). Some people actually have standing water under the floorboards and need a lot of subfloor ventilation. I used to be on a hill where the people next door needed to pump out their cellar in wet weather.

It will be interesting to see how damp the rubble is inside your cavities. I have known it damp enough to build a sandcastle, but not running wet unless there is a leak.

RomiiRoo Fri 25-Dec-15 21:23:49

Wow, this is interesting, thank you. I have a 1960s property which suffers badly from condensation, and the damp is in areas which are badly ventilated. I was thinking of getting a dehumidifier - is that sensible? I live in a very wet part of the country.

I also note the advice about keeping the heating on low, that makes sense.

My garden is clay, which is water logged at the minute. I always wondered whether that would make a difference but from what you say, it seems not.

I hate to jump in a thread which is not mine, but one question - if the rendering is causing what looks like patches of rising damp, are you better taking it off. And if damp-proofing companies are potentially going to rip you off or sell chemicals, who do you ask in RL? OP seems to have consulted widely, but i don't know where to start. confused I clearly need to start my own thread.

PigletJohn Fri 25-Dec-15 21:32:24

if your rendering is cracked, bubbled or loose, it will hold water against the wall. If you hit it and it falls off, that's a bad sign.

Sources of damp are usually condensation, defects in the wall, raised ground levels and blocked airbricks, or leaks from roofs or pipes. Sometimes badly fitted replacement windows and doors. A wrinkled old builder will have seen it all before, but you need to get personal recommendations for someone you trust. Online recommendations are sometimes written or censored by the trader.

If you drape wet washing inside your house, it will be wet.

Tape a piece of clear plastic tightly to the wall and see if water droplets form on the room side or the wall side.

Opening the windows is better and cheaper than buying a dehumidifier.

RomiiRoo Fri 25-Dec-15 21:58:17

Thank you so much. I need to get a builder in, no idea of any so will ask around. I am fairly sure the window is DDs room, which was a replacement several years ago was badly fitted, because I had the roof checked and the gutters are cleaned regularly by the window cleaner as part of his schedule. There is a crack across the plaster at the top of DDs window and the worst damp is on that wall. I will try the plastic bag thing, curious now.

The rendering, the damp is up the wall, I don't think it chips off, I will check.

Yes re washing, I have read you saying this before. It is impossible to get stuff dry here except in summer months and even then, blink and you miss the dry days. I am about to get a washer-dryer, but I am not sure what else to do. That is why I wondered about the dehumidifier.

Thank you very much for your reply anyway, it is my resolution to get it sorted in 2016 and the pointers are helpful.

tittysprinkles Fri 25-Dec-15 22:06:32

RomiRoo nice for someone else to join this damp thread! I am becoming somewhat obsessed with it as a subject matter and have bored off all my relatives with it today... The more I read the more it helps me to figure out where our new damp is coming from. A job for after Christmas though I think.

I don't think there is an issue with our watertable and I don't know if the ground has been raised in the past but our airbricks are virtually just above the floor outside - not sure if this is where they should be?

PigletJohn Fri 25-Dec-15 22:21:22

they should be, at the least, high enough for water not to run inside from any puddles. The dpc is probably on top of the airbricks, and should be nine inches above ground level, so that rain will not splash up onto the dry wall.

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