I’m intrested to know if anyone here has experience with blocking disused chimneys.

I live in a 1890/1900 mid terrace in london. We have one chimney with fireplaces in the living room and bedroom above. The previous owner had boarded up the fire places with no means of ventilation, and when we moved in we had to replaster the chimney breasts where the plaster had blown, presumably possibly because it had got damp.

I now want to again close up the fire places to kill the draughts and had initially thought to do this by boarding them up with a ventilation grille. Is this still the usual way to go about things, or can you now get some sort of fancy full fill insulation? I’ve seen some places advertising a full fill of vermiculite but this sounds heavy handed to me.

any thoughts on how to stop the big red chap would be welcome.

I put a length of down pipe in mine then filled around with expanding foam, then boarded the front with a grille. 10 years later it was fine (moved out now).

Cap the top to prevent damp.
Rain coming in with no where to go causes it – stop that no need for vent

You can get chimney pots that block off the tops of chimneys but have ventilation holes. And a bin bag full of scrunched-up newspaper will block the chimney at the bottom, but leave a little space for ventilation at each corner. The damp will be from soot and stuff which attract moisture. It might be worth getting the chimney swept.