Condensation on inside wall from old chimney flue?

[Sl8z]

Hi all,

We live in a 1930s semi, we have an old chimney flue outside (old cooking flue?). A this time of year we always get condensation on the inside bedroom 3 wall, definitely not damp as it dries out very quickly with a window being open (difference inside to outside temps). We've had the roof above checked, there were a few issues that have been taken care of as battens were wet under the tiles. The old chimney above the tiles was removed some time ago. There is an air brick top and bottom, I have temporarily sealed these off with some rubber and silicone. We still see condensation on the inside wall although not as bad without the air bricks covered up.

Would it be recommended to fill this void with insulation and if so what sort of insulation bearing in mind I would need to remove the top air brick (I uncovered this while investigating) and have limited access the whole way down? Could expanding foam be used or would that cause a bridging affect?

Am I also right in thinking that if I filled it with expanding foam and there was an issue, can small amounts of petrol melt the foam or is there an easier less dangerous way? I read that WD-40 can dissolve it?

Thanks all and any help/ recommendations would be really helpful,
SL8Z

 

[^woody^]

A flue needs to be ventilated top to bottom to prevent internal condensation - which will then cause a reaction of the old flue gas chemicals and create a bigger problem when this starts to leech out the walls and affect mortar joints.

You are better off lining the wall with insulated plasterboard if this is a regular problem..