Damp where removed chimney breast used to be

[Leffemonster]

I've recently discovered some bad damp on an upstairs bedroom wall in the area where a chimney breast has been removed, and also around the light socket. The wall concerned is an external wall on an 1881 Victorian terrace with no cavity, with the outside of the wall rendered. I've been into the roof space and there are no signs of moisture on the inside of the wall there. I'm at a loss to understand what is causing the issue as there is no chimney breast left, and no remnant of the stack (that I can see) on the top of the outside wall either, i.e. no capped-off chimney, so I dont see how water ingress can be possible through a rendered outside wall. I've attached pictures.

Any guidance is greatly appreciated.

Damp wall 3

• Leffemonster
• 18 Feb 2014
• 1

Damp wall 2

• Leffemonster
• 18 Feb 2014
• 1

Damp wall 1

• Leffemonster
• 18 Feb 2014
• 1

 

[ree]

Water ingress through a rendered wall, esp with recent weather conditions, is very common.

You have to get up there and carefully examine the render, all around and above the estimated position of the internal marks.

If the soot was not scrupulously cleaned off, and blinded when the c/breast was removed. Then sulpherisation (a chemical reaction to moisture and soot) could be taking place.

However, i dont see the usual signs of sulpherisation but you wouldn't know until the plaster is taken back to the brickwork.
If the plaster is contaminated then it will have to come off from floor to ceiling over the c/breast area.

The plaster in the pics appears to be a non remedial mix. Whats best is a sand: cement: lime mix in 4:1:1 proportions and a board finish. Or use remedial stuff such as Limelite.

 

[Flyboytim]

The light switch has a nice circle of damp around it!

From the various coloured wires in the light switch, it appears to be a 2-way switch perhaps?

If the wires are running through conduits from floorspace to the loft void, there is probably some air flow which could be chilling the metal switch box, and there is condensation with warm bedroom air and the cold loft air that possibly gets drawn through the box.

If not due to air flow by that route, could simply be due to cold brickwork in contact behind the box with cracks and voids in the mortar layers due to age that is being chilled by the outer skin of the solid wall. The render is probably adding to the chill of the wall by not being able to dry off itself under the wet conditions. The principle is the same as a terracotta wine cooler.

The bed was likely up against the lower part of the wall there, wasn't it?

Again, condensation due to a cold external wall not being warmed by airflow, with the bedding insulating the immediate wall surface, but allowing water vapour to condense there. Look behind other furniture in the room and the rest of the house for signs of damp.

Get some air movement in there to warm up the wall - not extra heat, that will only make the humidity worse, but just to warm the wall to an ambient temperature. A desk fan is ideal since it can ventilate a large area at lowest speed. Open windows a crack during dryer weather to increase ventilation. Keep the room a little cooler, and try to keep the temperature more or less constant, as fluctuations in temperature (and thus humidity) lead to colder surfaces meeting warmer moist air, and thus condensation.

If there has not been any sign of damp there before, it will probably be transient. The conditions this winter regarding UK rainfall have been extreme.

Everything Ree says is perfectly sensible, and worth considering if it will not easily dry out with ventilation alone.