Mould in corners of several rooms

[DJB]

I've read with some interest many of the previous threads on rising damp and disparaging remarks about the value of a chemical DPC. I have been trying to solve a damp problem in my house for the last year. The house is around 70 years old. I was keen to be certain of the diagnosis before embarking on expensive and disruptive reparations. The damp (and susequent mould) has appeared in the same place at opposite sides of the house, both at floor level and in corners. On one side of the house this affects adjacent corners of two different rooms (common source seems likely).
I initially thought that the damp in these rooms was secondary to water ingress around the chimney lead flashing - this was clearly a cause of water ingress and was replaced about 9 months ago. Unfortnately the associated damaged tiles were not replaced at the same time but been replaced now (2 weeks ago). There is brown water staining on the (new) plasterboard above the fireplace but this has dried. The fireplace is on the same wall as the damp. Between the fireplace and the damp corner is a built-in cupboard. I have removed this. At floor level nearest the brick work, the floor boards are visibly damp. The plywood back of this built-in cupboard has wrinkled from chronic damp exposure - worse at the floor level. The brickwork behind the cupboard is only one-layer thick (125 mm) unlike most of the other walls which are around 315 mm thick (with a cavity, I think). The outside wall is rendered and apart from a few bracket holes from an old (now removed) down-pipe some 3-4 metres from cupboard wall, the render is intact and solid. Under the floor, I can see a slate based DPC which is reasonable condition but with at least one or two gaps (air where slate should be). At the base of the chimney stack at the solum level, old rubble/ash has been heaped up and could be bridging the DPC. This could cleared away without too much trouble.

At the other side of the house, damp is occurring in exactly the same place behind an identical built-in cupboard. Again this is next to an old fireplace but on this side, the chimney has been removed (only visible in eaves) and the gap in the wall plastered over. Again under the floor rubble in contact with the external brick work.

You might say that I have identified the cause of the damp but I'm still not sure. Possible causes:

1. Defective DPC in single layer brick-work behind cupboard. Previous threads say this is unlikely.

2. Condensation. I don't buy this. These rooms are not in use, are heated and are not near bathrooms or kitchens.

3. Rubble in solum space bridging DPC and preventing air circulation.

I have unfortunately just ordered DryTech cream to perform DIY chemical DPC (only £120). I was quoted £2500 for damp-proofing (plus 25 yr guarantee) for chemical DPC and re-plastering so I am relieved that didn't go ahead with this work.

Comments please.

D.

 

[Gervase]

Chemical DPCs can and do work in brick, and the cream technique is the most (only!) reliable method - so your £120 may well be money well spent! Just ensure that you saturate the mortar bed well, and don't drill into the brick instead (which is what an awful lot of the expensive damp-proofing cowboys do).
I'd remove the bottom of the render outside as well, to expose the existing slate course, and remove the rubble. But it sounds as though you're on the way to getting the problem sorted.

 

[PC]

You've got a physical damp proof course and mould in the corners and you dont think its condensation!

I would hold up on buying that damp proofing cream if I were you and get a second opinion.

PC

 

[Mark]

I would clear the rubbish from the dpc anyway.

I have always understood that mould meant condensation.whats the ventilation like in the room. (heating wont do much if all you are doing is driving moisture out of the damp wall into the air and then not gettin gthe air out of the room

 

[DJB]

Thanks for the advice.

I have already ordered DPC cream (yesterday) so will almost certainly go ahead with the chemical DPC. I'm still not sure how extensive an area to treat. Should I treat the adjacent cavity walls and should I treat both leaves of cavity wall (this will require unpleasant under-floor drilling in a confined space)?
I don't think that condensation is the likely cause for several reasons. As I've said, the rooms affected are not used at all (half-full of boxes and undecorated) so where does the moisture come from to condense? Condensation doesn't explain visible damp patch on floor.

D.

 

[Nemesis]

I have to say I agree with PC - who is an independent damp and timber consultant by profession - if you already have a physical DPC why do you feel you need another?

Certainly the removal of rubble and as Gervase says ensure the render isn't bridging the DPC would be my priorities.

 

[PC]

How about condensate (water) running off the wall on to the floor?

Cold bridging, if solid floor?

Mould is normally always associated with Condensation and not Rising Damp!!

PC

 

[Matt Green]

Listen to PC.

Matt

 

[biffvernon]

We've got damp patches appearing in a couple of places near the floor. I do not believe there is any chance that water can be coming up, down or through this particular wall. My humidity meter has been registering record high levels for the last 10 days. Condensation from warm, wet air onto cold walls is the obvious cause.

 

[DJB]

Sorry, I don't wan't to argue with an expert but I don't get this. I accept that there maybe moisture in the house ready to condense on a cold surface. So it condenses on 2 or 3 isolated areas in parts of the house most removed from moisture sources? The damp/mould is only found around these 2 cupboards which both have common weaknesses. Both are adjacent to chimney stacks and more importantly are backed by brick which has no cavity and is only one layer thick.

D.

 

[Nemesis]

Well Matt is pretty expert too...

(and that's no reflection on you Biff...!!)

Hang on though - if th repairs have only been finalised recently isn't there some chance that this is residual moisture in the walls from the leaks?

And removal of the rubble would be a very good idea!

 

[Lime]

I, too, agree with PC.

Corners of rooms often have the poorest air circulation and mould does not normally appear where there is water penetration through the bricks.
Partially enclosed areas, such as behind cupboards, suffer very poor air circulation.
Water easily condenses out in poorly vented, colder areas whilst evaporation hardly happens at all in the humid still air.
As for rooms not being used, that does not mean condensation cannot occur.
A closed room is perhaps more likely to suffer condensation because of poor air circulation and few changes of air than a room with windows and doors regularly opened.
Also the single brick wall is much more likely to be cooler than other better insulated walls in the same room.
If it is suggested that water is somehow entering the room via the chimney then a DPC could make the situation worse and it certainly will not make it better.

 

[Andrew Bodenham]

Your problem sounds like an accumulation of contributing factors:

the room are unused , so air circulation and ventialtion will be poor,
the mould is occuring low down on the coldest (single skin) part of the wall. These two things alone suggest a condensation cause.

Then, external render may be trapping damp, and external ground levels may be contributing.

I'd think condensation first, then look at removing the render and ensuring that the dpc was not being bridged externally.

How about lining the single skin areas with slab insulation or insulated plasterboard? This would create a warmer surface and provdide a vapour barrier against the damp wall.

If the fireplaces / flues are not used you may be getting plug of cold damp air trapped in the botttom of the flue. I'd look at the flue ventilation arrangements.

 

[MdB]

In my old house, we got mould growth in the corner of the living room behind the sofa. This was very clearly a condensation issue as we could rule out the other causes. It wasn't rising damp as the lounge was on the first floor. It was unlikely to be penetrating damp as the house was a 1980's lump with cavity walls. The room was miles away from the kitchen and quite a distance from the bathroom so that was the unlikely source of the moisture. It was also the room we used the most so was both heated and had a lot of air movement in the majority of the room. So why did it go mouldy? Our conclusion was the moisture came from us breathing in the room and it condensed in the coldest part of the room (an exposed corner of the house). It couldn't evapourate as the sofa was pushed hard up against the wall and hence there was no air flow to keep that part of the wall dry. The solution was simple, we pulled the sofa 50mm from the wall and never had another problem.

DJB, you say that your room is unused. Do you keep the door shut? If so this might be enough to keep the air movement low enough to stop the evapouration cycle from working. Certainly in our new house, if we keep the door shut on our spare room you get a musty smell very quickly. Ventilation cures this.

 

[biffvernon]

...adjacent to chimney stacks...

Just the place with the highest thermal mass - in summer this will be the coldest spot when the warm wet air floats past.

 

[DJB]

Thanks for helpful comments.

In fact now that I think about, although damp occurred in 2 places in opposite sides of the house (well 3 actually if you include the adjacent corners of 2 neighbouring rooms), the damp patch on one side of the house was never mouldly. This was the room without the fireplace (previously removed). The damp patch was triangular with a broad base at floor level and was only in the corner (next to cupboard). The plaster had become covered with fluffy salt deposits.

I had assumed because the damp areas were close a common 'weak' area that the cause might the same. Perhaps the mould on one side of the house is condensation and rising damp on the other side?

D.

 

[Lime]

You could well be right.

 

[Matt Green]

Sounds like progress. The ground level damp patch now falls squarely into the Damp FAQ, so:

| We need to know:
|
| floor types (on either side for int. walls)
| ground heights (difference between ext. ground and int. floor)
| plaster type
| wall construction
Solid, single skin?

| problem being experienced
Salt deposition on the wall surface?

| what the room is used for

The quest to find the cause rather than just deal with the symptoms continues....


Matt

 

[DJB]

I haven't seen and can't find the Damp FAQ.

The floor is solid oak. The external ground level is considerably lower then the internal. The walls are a mixture. Without having seen the cavity, I think that they are mostly 2 skin with a cavity. The 2 walls backing these cupboards (with the damp) are single skin.

As I had already ordered DPC cream (Wykamol DryTec), I decided to go ahead and inject around this wall from outside (behind cupboard and about 60 cm either side). Under the floor I have removed bridging rubble that was up against the internal DPC. In general you can see that below the DPC the bricks are moist and above dry. However in bricked-up area underneath the fireplace the bricks above the DPC are also damp. I can't tell whether this is due to the previously mentioned rubble or a defective DPC. I am reluctant to risk damaging a good slate DPC by drilling into it unless I can be sure that it is defective.

Taking into account the above comments, I intend to put an air-brick vent behind each cupboard before putting the cupboard back in.

D.

 

[Nemesis]

Personally I'd have just removed the rubble which was probably bridging the DPC!

Don't damage the slate!!!