Is This Condensation or Rising Damp?

Roger tries to figure out another damp issue, or does he?

Here's our message from Jordan:

We moved into this property about 5 weeks ago and have noticed that after the bad spell of rain, the wall has a big wet patch with mould appearing.

We had a survey done before we moved in (the dampness wasn’t present then), highlighting the damp but putting it down to condensation damp.

Since moving in, we have had 4 damp specialists around who have since quoted us for different bits of work but have all said it’s down to different things.

This is our first house, and we don’t know what to get carried out as some of the treatments were costly. Can you help identify what it actually is? Rising damp or condensation damp etc.

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#risingdamp #diy #homeimprovement

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[jannenreuben]

There's a lot of things going on here as usual but I'd wager the root cause is simply condensation - warm moist air from the room hits a cold spot in the lower corner of the wall and condenses. Damp wall surface then provides nice conditions for mould to grow. To make it worse, the damp wall is prevented from drying out by inappropriate use of modern materials. Looks like somebody has tried to fix it in the past with an air vent into the cavity but this is probably just keeping it cold.

Solutions inside - better ventilation of room, remove wallpaper and paint using clay paint or other natural breathable paint. Keep an eye on internal humidity levels and temperature. Check under the floor if possible and make sure any void is clear and well ventilated. Remove laminate flooring and membrane (if fitted) so floor can breathe.

External - remove cement pointing and repoint in hotlime where necessary. Check cavity is clear of debris. Check drains / galleys/ gutters etc. are working properly and not blocked.

General - Be wary of damp companies. Most of them are complete monkeys who will wreck your house with useless tanking and injections. Spend your money instead on a copy of "The Warm Dry House" by Peter Ward which will help you understand what is really going on with damp.

[thesunreport]

I'm guessing it could be both problems. There are obvious condensation drips coming down the walls, but the internal mould goes up higher than I think a localised condensation problem would go. Looking at the pointing around that front corner I think there might be water ingress/entrapment, especially with the wind, and there must be enough water to keep the moss alive. I would definitely get the pointing done (properly) especially around that front corner/edge where it meets that other wall, get all of the moss out and do the pointing on those lower sets of bricks as well.
After all the condensation could be coming up through the wall and out of a crack under the windowsill or something rather than simply moist air from the house. That's my guess anyway.

[mnqugdm]

That outside corner seems to be very green and has a lot of moss as those the gutters been leaking and splashing back on that corner making it wet and a cold spot, I’d check that when it rains first then maybe paint that corner with storm dry, it has had a chemical damp course at some point can see drill holes that have been repointed

[sergiofernandez]

Pull out the air brick. Have a look inside the wall. Could be full of rubble or wet rock wool. See what internal ventilation there is if any

[dovedaledampcureserviceslt]

You can even see the drips that have formed and run down the wall.

[markmcqueen]

I've had similar problem for the last few years, and i recently had the company who injected the cavity with insulation 19 years ago, come out to investigate and after drilling holes for a small camera they found that the insulation had dropped and was causing moisture to transfer to the inside walls.
So now they are going to have to extract all the insulation from the cavities and make good internal damage and re insulate.
And reinstate a 25 year guarantee.

[oldwhizz]

I agree, too few pictures.. seems to be in the corner/rising, so could be from the rendered wall, from higher up, from the front, from a blocked drain, etc..

[johnmusgrave]

The airbrick will keep the caviy cold which in turn will cool the inner leaf of the wall. All you need then is moist warm air in contact with the cold spot and condensation is inevitable.

[alanyoung]

Came across a similar problem to this a couple of years ago after a so called “specialist” had jumped to the conclusion the affected wall needed 10k worth of rising damp treatment. In that case it turned out to be an obstructed cavity transferring moisture to the internal leaf. This then became cold as the dampness reduced its thermal performance, which in turn resulted in surface condensation as a secondary source of damp.

My approach would be initially (especially in winter) to monitor internal Relative Humidity to establish is this is persistently high (normal is usually between 40 & 60%). If so, or if the house is poorly ventilated, anti-condensation measures (extractors & trickle vents) are probably needed. I would also take a few initial surface readings to check if the wall surface is near dew point. The green paving externally may also suggest that rainwater spillage is taking place in this area.

With cavity walls, the outer leaf should be separated from the inner leaf by an effective cavity, which acts as a barrier. DPCs/DPMs also form barriers to internal damp transfer. Therefore, if dampness is present to the inner building fabric of a cavity wall it is probable that either: 1) The cavity is incorrectly formed or, more likely, compromised, and/or 2) The DPC/DPM arrangement is incorrectly installed and/or compromised.

It follows that, in the case of cavity walls, it is necessary to verify the efficacy of these barriers during the early stages of an investigation for internal dampness.

[leeberry]

Hi Roger, the pointing does look a bit ropey but I don't think that is the problem. That is a condensation problem which can easily be overcome. Well done for your diagnosis.

[KendalSmithy]

The dribble marks down the wall indicate condensation. Plus the cavity may be full of rubble which could let some moisture through but it would also reduce the insulating qualities of the cavity and make the inside wall colder than it should be.

[keithwebb]

A fair amount of moss on ground close to the wall suggests a north facing wall so it's never going to feel the heat of the sun and will always seem cold.
Poor movement of air inside will add to the problem.
That's condensation.

[gregwood]

I actually had a very similar problem. In my case plasterboard had been incorrectly dot and dabbed to the solid wall as there wasn't a continuous line at the perimeter of each board. As a result cold air could come through the below floor air brick, which was in a similar position to that shown here and creep up the gap behind the plasterboard. The cold then led to condensation. As soon as I put PIR between the joists, the problem went away. I suspect a similar issue is happening here, although if as Roger says, this is a cavity wall, air would be coming up the cavity rather than behind the plasterboard and could be fixed with the installation of an airbrick sleeve.

[markmcgrath]

looks like a cold area by the airbrick causing mould a low level ! also bridging damp coming from the external rendered wall !

[beijingbond]

Bang on, Roger. I had a terrace house that was built around 1844. My neighbour asked me to look at his house as it was black behind his wardrobe and curtains. I asked him if he ever opened the windows. His answer: "Nope". He wiped the mould off and made sure he had a window open when he showered and cooked. Problem solved.

[dociledeer]

When I was inspecting houses in response to a dampness complaint I found that (generally) black mould and only black mould is condensation, some black mould with yellow staining was structural/penetrating dampness. Best way to find out is to dig a wee hole in the plaster and get the protimeter on to the brick, if the brick is dry then it’s condensation. Thank god I’m not doing that anymore. 😊

[maheshpandya]

Hi Roger - Poor ventilation leading to condensation

[mark]

Check the humidity with a constant monitor . Monitor the surface temperature and the internal temperature, if the surface is below the dew point condensation is inevitable.

[peepiepo]

The lines running down make it look like condensation certainly

[sharonclaridge]

Looks like the wall in our porch before we started to leave the window open - all fine now. Well actually it's bollock freezing out there with the window open but it's too small to have the dehumidifier out there so although it's cold, it's dry cold and doesn't smell fusty.