Internal damp

[Marion James]

We have recently had the outside of our clay lump house painted using Masonry paint - this was 4 months ago and we have just found black and grey mould on some of the inside walls - could this be anything to do with the sort of paint we have used?
If so, is there anything we can now do about it. We have been using a dehumidifier to try to alleviate some of the problem.

Can you help?
Many thanks

 

[robgil]

it could be part of the problem , yes. however you need to find out why the walls are getting wet in the first place , also some more info might help.
what are the inside walls finished with? plaster, paint? what type of floors do you have? any pics of both sides of the wall?
clay lump should be rendered really, is there a render on the out side of the house?

 

[Flyfisher]

Hi Marion and welcome to the forum.

Could you give us all a bit more information about your house such as how long you've lived there, if you've had any damp problems before, that sort of thing. Nothing too precise, just enough for us to understand if you know the history of the house and how it has behaved in the past or if you've just moved in and therefore know little about it's past behaviour. For example, if you've lived there for many years and without any similar problems until the outside was painted than it would be a strong clue.

It's certainly possible to imagine that a previously breathable house might react badly to being given a waterproof coating. Woollen (i.e. breathable) gloves won't make your hands sweaty but rubber gloves will very quickly do so by preventing moisture escaping from your skin. People breath out huge quantities of moisture, plus we cook, boil kettles, have baths and showers and all that moisture has to go somewhere.

Mould usually makes me think first of condensation. When you say 'some of the inside walls' do you mean the inside face of exterior walls (i.e. those likely to be cooler than others) or some of the internal dividing walls. Also, where are the affected walls? Bathroom, kitchen or other areas of high humidity? If so, what are your ventilation arrangements?

Apologies for asking more questions, but it all helps to diagnose what might be the problem and, more importantly, what might be the solution.

 

[Penners]

Mould usually makes me think first of condensation.

Hello Marion - welcome.

I entirely agree with everything that Flyfisher has said. Damp is a tricky blighter, with many possible causes and many possible solutions. Solving the problem of damp usually means working through a series of suspected causes and then waiting to see whether you've succeeded. Needless to say, it's best to start with the cheapest, easiest solution first!

As FF said, internal mould is often associated with condensation. So as a first step it's important to know where the mould has accumulated. Is it in the kitchen or bathroom? Or perhaps in a part of the house where there isn't much ventilation? Condensation can often be resolved by the relatively straightforward expedient of heating and ventilating the affected area.

It would also be helpful to know what your rendering is, underneath the new paint. Is it cement or lime mortar? If it's cement, then the paint is unlikely to have made much difference to the breathability of the walls, but if if it's lime, then it's possible that you may have created a situation akin to FF's rubber glove analogy.

 

[chuckey]

Condensation usually appears as black mould at the bottom of recesses or in bottom corners of a room. Places where there is low air flow and the temperature is lower then in the rest of the room. If your bedhead is against an outside wall, this a good place to look.
Frank

 

[Marion James]

Hi everyone - thanks so much for all your replies and I will try to answer everyone's question in one e-mail.
We have been in the house almost 5 years and this year is the first time we have seen this damp problem. Chuckey is correct that it seems to be appearing behind stuff i.e. beds, cupboards and even inside an integral wardrobe.

We believe the render is cement, not lime mortar.

When we bought the house, we had a full survey and no damp issues were identified.

I should also mention that about 6 months ago we had new double glazed windows installed - prior to that it was just wooden single framed windows. Internal condensation on the windows has now almost been eliminated.

The damp seems to be on the internal face of exterior walls and at the moment it's solely restricted to the first floor but not the bathroom - it's affected all three bedrooms on their outside walls and behind something i.e. bed in one case, chest of drawers in another case. We have not seen any damp on the ground floor at all.

We open the new double glazed windows each day onto the safety catch i.e. with about an inch ventilation in each room.

The internal walls are finished with paint over plaster and upstairs floors are traditional timber joists.

The dehumidifier has worked to a certain extent as there was about a pint of water in it after 3 days of use in one of the bedrooms but nothing excessive.

I wondered if the new external paint is stopping the evaporation of water from the clay lump walls and therefore the water it is now coming into the house and trying to evaporate inside but not able to and therefore appearing as black spots?

I hope I have given enough info but understand this is not an exact science and will try to answer any further questions.

Thanks for all your assistance so far.
Marion

 

[robgil]

Marion what is the internal walls plastered with, do you know? also ,what are they painted with?
it sounds like condensation. is there a dpm in the floor?
basically when you seal up clay lump its can still be ok if it is kept dry although its not advisable to do this. The sealed clay lump and the cause of the damp might not be directly related although the effects of the damp may be. Have you any idea what the humidity levels are?
clay lump should be built on a brick plinth , this plinth should not be rendered so any moisture from the ground/floor can evaporate out through the plinth and not the clay, can you see this plinth from outside?

 

[Flyfisher]

I'd say we have a picture emerging here:

- The house has been known to be damp-free (at least not showing the current problems) for over 4 years
- New DG installed six months ago, formerly SG windows
- New external masonry paint 4 months ago
- Now seeing mould on the walls for the first time, but only in first floor rooms
- The distribution of the mould is in all the classic, poorly ventilated areas, implying a surface condensation problem

If nothing else about the house has changed then these new works must surely be the main suspects. It's a shame both the recent changes were made at pretty much the same time, which makes it difficult to isolate the main culprit, although it's possible both are contributing to the problem.

Assuming the previous windows were airtight, then I'm not sure how DG would contribute to the damp and mould, whereas it's perhaps easier to imagine how the external masonry paint could have reduced the overall breathability of the house.

Assuming that the living habits within the house haven't changed much over the past five years, I wonder if the previous SG windows resulted in lots of condensation on the cold window panes and whether this condensation was mopped up daily, or at least fairly regularly? It's only a guess, but I'm wondering if the SG windows were the previously coldest areas in the house where the internal moisture would condense? By removing these cold surfaces, with the new DG, could this have shifted the condensation to the walls instead? Condensation on the walls would be less noticeable than on the windows, so possibly not wiped up, leaving time for mould to become established.

As for the problem only being found on the first floor, could this be simply due to the bedrooms being generally colder than the ground floor rooms? Thus, warm, humid air rises to the first floor rooms and moisture condenses in the cooler, unventilated areas of the rooms.

I'm making a lot of assumptions though. I think they make some sense, though that doesn't mean there couldn't be other explanations.

Any other ideas?

 

[JohnB]

I've just been to a meeting where a builder who renovates old houses was talking about problems with a house that had new uPVC windows fitted. Apparently they weren't sealed properly, and water got into the walls. I wasn't clear whether this was lack of sealant around the window frames, or water getting in around the glazing units. It might be something worth checking.

 

[Matt Green]

smoking gun:

I should also mention that about 6 months ago we had new double glazed windows installed - prior to that it was just wooden single framed windows. Internal condensation on the windows has now almost been eliminated.

The single glazed windows used to be the coldest surface in the room, now the external walls are. It would seem to be a condensation problem in areas where there is no air movement. Try moving the furniture away from the walls as much as you can bear; consider moving furniture so it is not against external walls; consider moving a radiator onto an external wall; open up a blocked hearth to improve ventilation (?); dry-line the external walls; re-plaster the whole room in lime and decorate with beathable finish to remove the condensing surface....or occasionally move the furniture and spray the wall with mould remover.

It's a question of how much it bothers you and how much you want to be rid of it.

M.

 

[Penners]

Marion - I'm sure that Flyfisher and Matt have identified the most likely cause of your mould. You might like to know that Matt is a professional in these matters, and FF has plenty of experience of such problems.

If, as you suspect, the exterior rendering is cement-based, then I don't believe that a modern masonry paint is going to make a great deal of difference to its breathability (or lack of same).

 

[Flyfisher]

If, as you suspect, the exterior rendering is cement-based, then I don't believe that a modern masonry paint is going to make a great deal of difference to its breathability (or lack of same).

Oops - I missed that point in Marion's reply
In which case, I entirely agree, the new paint will have little or no effect compared to cement-based rendering.

So it's looking like the effect of the DG windows, which Matt homed in on straight away. I'm always happy to bow to professional experience.