Mouldy Wall

26 Nov 2015
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United Kingdom
I wonder if anyone can give me some advice-

In our back living room, the wallpaper was peeling off the outside wall, so I pulled it all down and discovered mould. Some of it is black dots, and some is white- looks almost like the white ice you get inside freezers. The wall is very cold to touch, and I could not decide if it seemed slightly damp. It was in places a bit crumbly, and some of the plaster came away with the paper. Also, in a couple of areas the top layer of plaster (maybe 5mm thick) had pulled itself away from the wall, making a sort of plaster bubble, which was hollow behind. I removed the loose plaster, and what I could of the mould, but I'm now not sure how to proceed- I want to properly treat the mould / wall so it won't happen again, but I'm a bit of a mould n damp n00b!- I'm not sure what caused it to happen in the first place, or what the best way to treat it would be? Ps, The outside of the wall was repointed and pebbledashed several years ago, and doesn't *look* damaged.
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A photo or two would probably help, not least to show where abouts on the wall the mould actually is......skirting board level, below a window or whatever.
The white stuff is what comes out of the plaster when it gets damp.
John :)
What you seem to have is more than mould or condensation.

Pics of the room wall(s) and a close up of the exterior wall and the larger wall elevation will help.

Is the wall and floor solid - or is there a cavity and a suspended floor.

Have you had retro-cavity insulation installed?

FWIW: there are two kinds of white stuff: one comes from condensation and the other from penetrating damp.
The white could be effervescence due to penetrating damp, likely if the dashing is in poor condition or cracked. Mold is due to the damp, remove one and the other cannot thrive.
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I took photos today. Unfortunately I'd already partially cleaned up before I knew I was going to want photos, so the mould isn't there in it's full glory any more, but you can still see a bit!

Full view of the offending wall:

Full view edited to show where the mould patches were:

Beside the window:

Beside the window (lower down):

Below the window- white mould was mostly where you see the chipped off plaster- there were also the plaster "bubbles" (raised bits with air behind) I talked about here, so what's missing there all fell away easily, either with the wallpaper, or when I "popped" a bubble.

The outside of the offending wall (full view):

And a closer view of the below-the-window part- as you can see it doesn't appear damaged:

What you seem to have is more than mould or condensation.

Pics of the room wall(s) and a close up of the exterior wall and the larger wall elevation will help.

Is the wall and floor solid - or is there a cavity and a suspended floor.

Have you had retro-cavity insulation installed?

FWIW: there are two kinds of white stuff: one comes from condensation and the other from penetrating damp.

The wall is solid brick- as far as I know no insulation or anything special inside- it's a very old house- some 100 years+ I believe.

The floor is 3 foot of solid concrete below the laminate- I am certain of this because I saw it go in!- around 10 years ago the council were giving out renovation grants, and we had a lot of work done- they dug up that whole floor and redid it. They also re-pointed the back wall and pebbledashed it, and replaced all the windows with double glazed ones.
Could be a poor seal around window allowing in moisture and the shrubbery looks like it make contact with the house , not good as it will keep the wall wetter for longer and prevent drying.If your gutters are blocked the rain is going to overflow against the wall and run down the outside of the down-pipe.Also worth checking the external tap for leaks and make sure the drain is clear.
As above, take particular attention to the underneath of that original cill just in case water is seeping underneath due to the drip groove not being there......also see that there is silicone between the window frame and wall.
It does look like a bit of a damp area outside - I'd lose the shrubbery, personally just to let the air in.
John :)
Yea, I'm going to cut the ivy back and pull it all off the wall again soon- it grows incredibly fast! I swear it's half triffid! But the side where it is is the side that was not mouldy, so I don't think it's the cause?

Gutters are also on my to-do list but I'm pretty sure they're not overflowing- will pop out next time it's pouring rain (probably tomorrow then!) to make absolutely sure. It is a good logical idea- if it was leaking it'd be running down the outside of exactly where the worst mould is, but I'm 90% sure it isn't.

The drain is nice and clear, and yea, the tap is fine.

Good idea about checking the window seals, and I'll do that in the morning, but if it was that, wouldn't I expect to see some mould on the plastic part of the window and / or the plaster directly connecting to it? There was none on the plastic, and only a very few dots on the plaster right beside it- most of it is a bit further over.

I'm also ruling out a humidity problem inside, because that's the only wall that has a problem... UNLESS... is it possible moisture is caused when warm air hits the very cold wall? Like how you get condensation on windows? But why behind the wallpaper then? And why not more on the plaster directly touching the window where it's likely coldest? Hum. Also, oddly, the wallpaper behind and directly above the radiator came away quite easily too- no steamer required- it just pulled off in sheets, although there was no mould there. Seems odd that such a warm place could be damp?
Lots of good suggestions above.

Moisture is penetrating the old wall.
The main suspect would be the junction of the kitchen extension (cavity wall?) and the old wall. A pic of the flashing where the extn roof meets the old wall would help.
Next suspect would be the dashed render.
The smooth render near ground level seems to be in ground contact and bridging any DPC. A pic here as well please.
The gulley on the house wall is damp. A correctly installed gulley doesn't need a dam.
Does the stone cill have a sound throating?
Cut all the foliage well back.

remove the skirting board and examine it and the wall behind - all the plaster will have to come off eventually and be replaced with lime and sand render. The rad will have to come off for any remedial work.
remove the chest from the chimney breast recess and examine the wall & skirting behind. Check for the edge of a membrane (DPM).
examine the wall and floor in the kitchen.
there will be a certain amount of humidity but thats not the major problem.
Have you examined the room above?

Its doubtful that you had 3ft of concrete - more like 6" - why not research conc floors on here.
You've got classic condensation mould, in a typical Victorian terrace. The patches are the giveaway, as is that location on the rear wall, which is rendered and that does not help.

Mould only lives off fresh condensation moisture, and is being fed by the starch in the wallpaper paste.

The white bits are salts from the plaster which once drawn out, start to absorb more moisture from the air to get worse and worse.

You will need to deal with your condensation by reading up on it, and then hack off all that plaster and redo it, as once the salts are drawn they will continue to be.
Oook what a lot of stuff to respond to! :LOL: Thank you all!

I tried to check the seal around the window- I couldn't see anything- pebbledash covers it all.

I checked the gutter- there's no blockage / nothing leaking. It was raining (as usual) when I looked.

I had a look under the windowsill- there isn't much of an under, nevermind a drip groove (the spider's name is Henry btw- I did ask if he would move for the photo, but it was raining quite hard, and he didn't want to get any wetter).

I photographed the flashing where the extension meets the main wall- btw my dad says the extension is part of the original house- even though it looks like an extension, he was fairly sure it was built when the house was.

I photographed the smooth render where it meets the floor as requested:

I also noticed that the pebbledash has a sort of a lip underneath it where it meets the smooth render- it was difficult to show on stills, so I took a video of it:

I think the dam around the gulley is because.. well.. for some reason I have no idea about, the drainpipe doesn't go directly into the drain hole...

Inside- removing the skirting board is not so easy- it isn't skirting board, it's boxing in. Even if I remove it, I won't be able to see much- all the central heating pipes are in there.

I had a more thorough look at the alcove wall- it all feels good (wallpaper well stuck and nothing crunching behind) except for the bottom 6" or so above the skirting board, where it feels maybe slightly damp and crunchy.

The wall and floor in the kitchen look fine:

Though there was once (a few years ago now) a damp problem there- there was a leaking pipe in the wall, I believe- in the corner of the kitchen wall you see in the pic above, there were mushrooms growing! It was fixed and redecorated, and no problems on that side since.

I couldn't really get to the lower part of the wall to get a good look without major dismantling- as you can see there's a cupboard in the way! I did get underneath it though. This is the other side of the mouldy wall- about where the radiator is, but at ground level:

I touched the plaster there to see whether it was damp, and a few chunks crumbled and dropped just with a light poke. :oops:

However, I couldn't feel any damp- it felt dry and crumbly? After the initial few bits dropped off, the rest seemed fairly solid, although obviously I didn't engage in TRYING to rip more off!

The room above previously had a damp problem on it's outside wall too- we could not find a convincing cause- thought maybe the gutter above, but the very top room has no problems at all. The mid-level room was replastered and redecorated about 2 years ago. No further problems so far.

As for the 3ft of concrete- well I don't know for sure what they put in there, I must admit- I wouldn't know concrete from other types of stone by sight, but it was a deep hole alright! :LOL:

Woody- could you recommend any good resources for learning more about this type of condensation?

Thank you all!
Excellent Pictures(y) That gulley needs both the black rainwater and white waste pipe altering so the water discharges into the hole - easy diy job and combined with removing the foliage will help.
Nice photos, but I would like to stop you before someone asks you to photograph the whole street.

If you have a damp patch in one part of wall, then you don't go looking for the cause all over the house and garden.

If you have several independent damp patches from floor to ceiling, then the cause is narrowed down, and it is not going to be a leak. Especially when there is no tell tale stain of an internal leak, or that indicative of water penetration.

You have a condensation problem. The location, the pattern, the type, the mould are all indicative and just can't lead anyone to suspect anything else.

Stop your goose chase, and deal with that. There are threads and the wiki here, or just putting those words into Google UK will throw up numerous results.
I agree with Nige F, the pics are great. And agree with what he said about the gulley pipes. You will also need a (150mm?) gulley grid.
Afterwards remove the dam kerb the mortar fillets, and cut back the wall render to 50mm above ground contact.

The under sink pics shows condensation on the wall: the plaster is in contact with the concrete floor.

Its nothing to be disturbed about.

As precautionary measures 1 to 4:

1. pic 6 shows cracks in the dashed render - moisture could be entering here, and moving down and into the wall. Have all render cracks sealed with polyurethane caulk.
2. Use this caulk to seal the dash to the window frames - there doesn't seem to be any sealant there at the moment.
3. Run a line of caulk on the cill underside - it will stop the water running under, & perhaps penetrating the render.

4. pic 13 cut back the render 50mm from ground contact. In pic 17 The bump at the bottom of the render is a Bell Cast and its supposed to be there.

pic 16 "alcove" shows what is possibly condensation - keep the chest away from the wall.

pic 20 the DSS outlet box is out of the wall.

The wall is undoubtedly a cold wall and condensation does seem to be the major difficulty, so i was wrong to think that penetrating damp was the major cause. However, i still suspect that very faint moisture penetration could also be taking place. No matter, the remedy that will give you many years of unstained decorations is to hack off and render in sand and lime. And to provide trickle ventilation and a constant low heat.

The exaggerated comments above are foolish in the light of what the pics have revealed - however, you the OP will have to judge whether
you think its been worthwhile to have more than one defect made known?

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