Solid brick 1905 house. There's a patch about 60cm across on an internal wall, on the side that backs onto the kitchen, that darkens from November and is completely gone by April. No visible plumbing on that wall. Wall feels cold to the touch in that spot. Two firms have quoted for injected damp proofing and replastering and I'm suspicious. Where should I be looking?
Seasonal, on an internal wall, cold spot, near a kitchen — that's condensation, not rising damp, and injected damp proofing will do nothing for it because there's nothing rising. Save your money.
What's happening is that spot is colder than the surrounding wall, so moist air from the kitchen condenses there first. Cold spots on internal walls usually come from something structural behind it — a chimney breast, a solid section, a bridged cavity, or a gap in insulation on the other side.
Diagnostics that cost almost nothing: a cheap hygrometer in the kitchen and the affected room, and an infrared thermometer to map the cold area. If the kitchen is regularly above 65% relative humidity you've found half the problem. Rising damp also doesn't do 60cm circles on internal walls, it does a horizontal tide line — the shape alone rules it out.
There's your answer then. A decent extractor ducted properly to outside, run during and for 20 minutes after cooking, plus a closed kitchen door, will likely make the patch disappear. That's a couple of hundred quid against a four-figure damp proofing quote for a problem you don't have.
Kitchen hygrometer is reading 72% most evenings. Extractor fan is ancient and I suspect it does very little.
Check what's on the other side of that wall too. A cupboard against it, a fridge pushed tight to it, or furniture blocking air movement will create a local cold spot for exactly this reason. Pulling a wardrobe 10cm off a wall has fixed this for more than one person I know.
Leave a hand's width behind it permanently. Combined with the extractor fix I'd expect the patch not to come back next winter.
There's a tall bookcase flat against that wall on the other side. Moving it this weekend.
If any of the plaster does need replacing later, use a lime-based plaster rather than gypsum on a solid brick wall. Gypsum traps moisture against the brick and you get a repeat performance in three years.
Do check for black spotting on the patch. Mould growing there is another confirmation of condensation — rising damp brings salts and a tide mark, not mould.
@immutable_infra · 5mo ago
Worth adding: firms that sell injected damp courses diagnose rising damp at a remarkable rate, because that's what they sell. An independent damp surveyor who doesn't do the remedial work costs a few hundred and is the right money to spend if you're unsure.
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