"Rising Damp" Internal Party Wall

[SWJR93]

Good Evening Everyone,

We've recently moved into an Edwardian end terrace house in Cambridge. It was originally a 2-up, 2-down, but has a single story extension at the back now (kitchen and bathroom).

We have discovered in our understairs cupboard some significant damp against the party wall (see floorplan and pictures). I knocked away the plasterboard (which was obviously exacerbating the problem) at the bottom of the wall and it was sodden/crumbly. It got drier as I went up. I took away some of the floorboards to reveal a very old tiled floor. The floorboards are rotten on the side that bridged the wall but dry on the other side. When I run my finger along where the wall and floor meet, there is a lot of damp sand-like material.

All-in-all the source of the water looks like it's coming from where the wall and floor meets.

I haven't been able to follow the wall along to see how far it extends.

There are no pipes that I'm aware of in that area.

I'd appreciate your expertise ... How panicked should I be? What are some of the potential fixes? I'm so dubious of a damp proofing expert coming in and telling me I need an injection. I want to actually fix the issue. What do you guys reckon? Damp coming from the ground on an internal party wall is weird right?

 

[IHateDamp]

I don't think you need to panic.
Sorry if this sounds pedantic, but when you say you removed floorboards, you mean the wooden flooring material laid on top of the tiles rather than structural floorboards on joists?
What do you think is under the tiles ? Concrete (solid) or wood (suspended floor on joists) ? What is the flooring in the rest of the building on the ground floor ?

Damp on the internal party wall is common at the base.

 

[SWJR93]

Forgive the ambiguity. I took the floorboards (in picture 1) laid on top of the tiles you see in the picture. I'm not entirely sure what's underneath, but our floor certainly doesn't sound hollow. There's no airbrick on the outside servicing the dining room, only the lounge.

I believe the lounge used to be suspended floor but was replaced with concrete slabs decades ago. The extension (kitchen) is concrete.

 

[Cubist]

A DPM may or may not have been installed when that concrete slab was poured - if there were you may find some evidence of the DPM at the perimeter of floor to confirm that damp rising from below is being pushed toward the walls and escaping via them. Should there be no DPM then damp rising through the slab would/should be more generally evident.

 

[SWJR93]

I've done a bit of research on other properties down our road, built at the same time I'm guessing ... These pictures show the quarry tiles in their original form, still existing in some of the properties - always in the dining room. As such, I'm thinking the tiles are an original feature? From what I've seen, these tiles used to be placed on top of sand?! I'm wondering if that's what I'm seeing at the edge where the damp seems to be spreading from. Anyone familiar with this Edwardian tile laying process?

 

[stuart45]

Wall and floor tiles used to laid.and fixed with mortar. Earlier.with lime and later cement. Tile adhesive is a modern method.

 

[IHateDamp]

The original way the quarry tiles were laid may have helped with evaporation rather than trapping it and pushing damp into the walls

The flooring on top of your tiles may have hindered evaporation. Now you have the floor more exposed the walls and floor are more likely to dry out

Old houses are meant to be breathable. Modern materials aren't. Furthermore, understairs cupboards are notorious for having poor ventilation, resulting in the surfaces not being able to dry. You could put ventilation holes in the door to help. If you have holes on different sides then so much the better; to allow a through draft. You could use breathable paints.

If you keep this area ventilated, clean up the black stuff on the tiles you may find it reduces or eliminates your problem

Reading this forum and books about older houses may help you to get a better understanding about damp in older buildings and reduce your worries.

Don't get your walls injected.

 

[SWJR93]

It's a party wall, so if the cause was the other side, it would be the neighbour's property. To the best of my knowledge, the neighbour has the same setup as us. I've let it dry out since discovering it on Saturday. Initial few days the dehumidifier was picking up lots of water. Now it seems to have slowed down vastly. Let's see what happens when it rains outside :/

 

[IHateDamp]

That's good news

In the unlikely event the neighbour had made their side of the wall less breathable eg by tanking the wall, then more moisture would likely to be pushed your way.

 

[Alex_]

There's no shortage of surveyors who can offer an opinion in Cambridge, there must be 1000s of properties of a similar age and design that have encountered similar problems. FWIW, I have a much older property south of Cambridge and we removed the gypsum skim over the lime plaster from inside an understairs cupboard a few months ago as it was coming away and was damp to the touch. It's completely dry now and our plasterer took the remaining lime plaster back to the laths to redo it and there's zero sign of any decay to either 200+year old laths, stairs or the sole plate that was under the plaster. Make it breathable, ventilate and you'll probably have no issues going forward.

 

[benoliver999]

There's no shortage of surveyors who can offer an opinion in Cambridge, there must be 1000s of properties of a similar age and design that have encountered similar problems. FWIW, I have a much older property south of Cambridge and we removed the gypsum skim over the lime plaster from inside an understairs cupboard a few months ago as it was coming away and was damp to the touch. It's completely dry now and our plasterer took the remaining lime plaster back to the laths to redo it and there's zero sign of any decay to either 200+year old laths, stairs or the sole plate that was under the plaster. Make it breathable, ventilate and you'll probably have no issues going forward.

We did this on a party wall. Cement tanking on the bottom, gypsum skim on stop. It fell off with very little effort, and as soon as the cement came off you could smell the damp. A few months wait later, we've now lime plastered the wall and it's dry and happy.