Sudden damp on internal walls?

[AkiraDIY]

My mother's house has a half subterranean floor, which was flooded in 2011ish. Scottish water or the council blocked a storm drain outside and about half a foot of water came in. They were playing the blame game and eventually my mother fixed it through her own insurance as it took out her kitchen and they were taking too long.

We were looking to repaint one of the rooms and when we got everything out, the paint was bubbling/flaking and salts were on the lower parts. When brushing the salt off, the plaster skim and part of the drywall came off and it was damp to the touch. The concrete floor is dry and the damp is on random parts, picture of the largest patch attached.

It's an internal wall of solid construction (old house, built approx 1888) and there's no pipework in that area. The room has been left cleared for a month now but it's not showing any signs of drying. It's been OK for the last 10 years (or slowly accumulating), any ideas what might be causing it now and how to fix it?

 

[foxhole]

When was it last ‘wet’.

 

[AkiraDIY]

After the flood, the builders took it back to bare wall, dried it with heaters/fans/dehumidifiers and then repaired it. As far as I'm aware, it's been dry since then.

Before the flood, wallpaper was up. The wallpaper never had any signs of mould or felt wet.

 

[foxhole]

Was this ever an external wall ? Then extended?

 

[AkiraDIY]

Always internal, I think the subterranean level was a much later addition to the 1888 main house, perhaps 1980s

 

[foxhole]

Below ground it would have been tanked which may have failed ?

 

[AkiraDIY]

That sounds expensive to fix! I'm hoping it's a condensation issue as this room isn't used much and is just off the kitchen. Looking at upgrading the kitchen extractor fan as it's quite old and I never believed it to be any good or some kind of PIV system. Probably a long shot though

 

[JohnD]

it's not showing any signs of drying

What ventilation are you providing to cause it to dry?

 

[AkiraDIY]

What ventilation are you providing to cause it to dry?

The room is now empty, flooring included. Heating is set to max for a couple hours a day and recently put a dehumidifier in the room to run in parallel with the heating. Needs the heating on or the coils ice up, somethings broken and not had time to get it looked it.

The latter seems to be having an effect although that may be more psychological than physical. Time and some bad weather will tell if its condensation or damp I guess although the skirting doesn't seem to have rotted so fingers crossed its the former

 

[foxhole]

The room is now empty, flooring included. Heating is set to max for a couple hours a day and recently put a dehumidifier in the room to run in parallel with the heating. Needs the heating on or the coils ice up, somethings broken and not had time to get it looked it.

The latter seems to be having an effect although that may be more psychological than physical. Time and some bad weather will tell if its condensation or damp I guess although the skirting doesn't seem to have rotted so fingers crossed its the former

So no ventilation?

 

[JohnD]

Absolutely.

Ventilation is what you need, and lots of it.

No need for expensive heating.

Put an ordinary household fan to blow against the damp wall to hasten evaporation

And open windows or vents on at least two sides of the room so a throughflow can blow out the damp air.

 

[AkiraDIY]

The room is internal so no windows. All trickle vents are open in the lower ground level and the kitchen window is open most of the day. Still looking to get the kitchen extractor upgraded but struggling to find a workman willing to do it or has the time to do so

I'll get a fan stuck in there too for the time being

 

[JohnD]

if no windows, you can run a duct.

flexible ducting is not much good, but would help as a temporary fix. It can be clipped to ceilings or walls, or rested on shelves or the tops of wall cabinets. Water vapour is lighter than air so extract at ceiling height.

I don't know if you can afford a powerful ducted fan? A cheap bathroom fan will attach to 100mm duct and is only about 80 cu.m/hr but you could run it continuously. Electricity cost is insignificant. A better quality fan can be quieter as well as more powerful.

Long term, any underground room needs good ventilation or it will be prone to damp.

 

[AkiraDIY]

Ceiling is too low for a duct. I think it's because the kitchen extract fan has gotten a bit **** over the years, cooking humidity is building up. If it were a rising damp issue, it'd expect the wet to be more consistent across the wall but it's the worst closest to the door, where the kitchen is.

If that's swapped and it's still an issue, I'll look into a PIV system. Not much else I can do I think

 

[Harry Bloomfield]

The room is now empty, flooring included. Heating is set to max for a couple hours a day and recently put a dehumidifier in the room to run in parallel with the heating. Needs the heating on or the coils ice up, somethings broken and not had time to get it looked it.

The coils can ice up, but the dehumidifier should periodically defrost itself. Try adding a fan to blow the air around, air circulation helps move the moist air to the dehumidifier.