The Answer to the Damp Problem

Back in August 2022 (for the first time in over 36 years of living here at the time) we began to notice some damp in the wall of a ground floor room, which prompted me to go on a "subterranean expedition" to try to identify a cause - without success as the underfloor area seemed dry (see my blip here).

In spite of not finding underfloor damp I then suspected that the drain under the ground just outside the affected corner (into which a major downpipe drained) might have fractured and started leaking. To test that theory I covered that gully with plastic sheeting and "temporarily" diverted the pipework across the bay window to another gully some distance away - you can see that in the left-hand photo in the diptych here. We waited a few months to see if the damp would go away after that, but it didn't.

My next theory related to the repainting of the brickwork on the outer porch by the front door. This brick was already painted with gloss paint when we moved in (we'd never have chosen to paint it) but it wasn't a good paint job. We'd had it redone many years ago but still not very well. So during lockdown I did the best job I could of repainting it (with supposedly "breathable" paint) - after all, it was a good time for some DIY! It was about a year after that when we noticed the internal damp - and I also noticed that the lower part of my new paint job was getting stained from behind. Conclusion: the brickwork was not managing to breathe as it should, because of the well-applied paint. (As far as I'm aware this 120-year-old house has no damp course but relies on evaporation from the brickwork to prevent rising damp.) So a few months ago I (rather reluctantly) stripped the lower paint again (see the right-hand photo): success - the damp disappeared within a couple of months! So today I finally got round to reverting the course of the downpipe to its normal position as you can also see in the right-hand photo.

Moral of the tale: Don't paint external brickwork in an old house with no damp course and solid walls!

This makes me very wary indeed of trying to add insulation (either internally or externally) to the walls of an old house like this. Much as I'd like to do my bit for the environment (and save on heating bills) I fear that even breathable insulation could risk causing serious damp.