Damp patches on internal wall

[overlander matt]

I've got a couple of problem damp areas on an internal wall that I'm not sure what to do about. I hadn't expected any trouble prior to painting - the wall was replastered with lime around 18 months ago and I had assumed it had dried out thoroughly. On applying the grey paint, a permeable emulsion from Rose of Jericho, there were a few dark blotches that over time have flaked off. The wall doesn't really feel damp but feels a bit different to the surrounding areas. I had not noticed any problems with this side of the wall prior to the work. The blue paint, a clay paint from Tilbrook and Fenwick, is on the other side of the wall but a couple of metres from the problematic grey patch. Previously, this side of the wall was very damp - with moisture trapped behind a gypsum plaster skim coat.




Some other background to this area - the grey side is the main house with a double skin of brickwork to the blue side that is a later lean-to addition. There are no pipes in the walls or below ground in this area (unless they're very deep), the solid floors in this area were raised by 200mm but they're not breathable. Directly behind the blue wall was an old fireplace which had really stained the brickwork on that side of the wall - I do wonder whether this could be a factor... Elsewhere in the blue room I have a bit of damp which I'm sure is connected to a high ground level - I hadn't noticed it was damp until I painted it. I've taken steps to eliminate the source of this damp and hopefully it won't return.

Just wondering what are the next actions in investigating this. Thanks in advance.

Matt

 

[worms]

No ideas for the grey painted area, but is the old fireplace directly behind the stained area in the blue room? If so, what is the status of the old fireplace and chimney? And what was used to board-over the fireplace opening when it was all closed-off? If the chimney is still present, with no means of allowing cold air to escape at the bottom, there will always be a risk of condensation carrying mineral salts (or other residues from the coal tar) through the wall.

 

[MatthewC]

I agree with worms re the chimney as a possibility, but what is the foundation of the wall and what is the wall made of? You presumably removed all the gypsum from the wall before plastering with lime, but if the wall has cement mortar...

 

[overlander matt]

Thanks for the comments Matthew and Worms. The wall in question was originally an external wall probably dating from Georgian times - it became an internal wall when a lean-to was added 100 years or so ago and is built of lime and brick. The brickwork in places (particularly where the fireplace was) was really quite poor and needed a fair amount of repair work before replastering. There must have been quite a fire there back in the day - it was possibly more than just a kitchen.

On the other side of the wall is now an enclosed area of kitchen units. This part of the building was originally a single storey and later a second storey was added without building any foundations for the fireplace. The chimney is above the units and remains partially open.

It's an interesting thought about condensation forming on the kitchen side of the wall. I can take a look behind the back of the units to see if there is anything obvious. Presumably the size and shape of the damp patch(es) would tend to change over time if this is the case. It looks like I will need to monitor this for a while before I work out what needs to be done.

Thanks again,

Matt

 

[worms]

Matt, so if I am understanding this correctly, the fireplace in the former lean-to building was entirely external to the original wall and has essentially been removed, leaving only the chimney, above cabinet level (presumably with suitable side supports still in place!). If that is the case, then the chances of there being damp associated with the chimney is much lower than I was envisaging, but perhaps still worth investigating as you suggest. Is there any potential for water penetration at the roof-line join between the old and "new" parts of the building? Is the external chimney still in place above roof level?