Damp on walls with concrete floor

[Adam-78]

I have a kitchen which has a concrete floor and appears to be covered in some bitumen type coating. On the walls Im seeing 'rising damp', more visible on a wall that has had gypsum plaster. On the other side of this same wall the plaster has all come off and you can see salts forming on the brick work. I can't see any visible DPC on this brick work but there could possible be some on the mortar line in one of the pics I'm pointing to.

I'm not sure if the concrete is sucking up moisture from the ground and because it's right against the wall and no where for that moisture to go because of the bitumen coating, it's moving sideways toward the walls causing these damp patches.

I've noticed the subfloor joist ends that sit on this internal wall where the concrete floor is are wet and rotting too.

Any tips on how I can fix this?

Property is a 1920's semi. Only the kitchen is concrete, the rest of the floor is of suspended timber.

 

[Cubist]

DPCs became mandatory in London in 1875 so even new-builds in Bury should have them by the 1920s. The black line you seem to be pointing to is about where I would expect to see the DPC material, i.e. at least two course of brickwork below any joists. The one external photo you include suggests that your exterior ground levels are much higher than they need to be and the DPC may have been comprised/bridged. Also, there seems to be a lot of corrosion of the copper pipes shown in both the 1st and 3rd photos. It may be an idea to check the pipe runs below the floors surface in each the rooms concerned as a pin-hole leak may be a source of water accumulation in the walls.

 

[DaveG]

I will do my best to give tips on how to fix but not quick or straightforward I’m afraid.
As I often say in other similar threads, damp can be tackled on multiple fronts. Choose the one you’re most comfortable with first as doing that one thing will help but may not cure alone. Still, to go one thing at a time is less invasive and may help you reach an equilibrium where you’ve not eradicated the damp completely but you’ve got to a point you can manage the moisture away without too much pain if that makes sense.

Step 1 I would say is letting the moisture have a route of escape. Plaster falling off the walls is a sign it’s doing just that….trying to escape. If you can remove the gypsum back to the brick indoors the moisture can evaporate.

It’s really important that you have sufficient airflow particularly as it’s a kitchen meaning it’s already a heavy moisture producing room. Windows can be enough in some cases but you need to think about air movement across the room so you may need to consider some sort of extractor in your kitchen if you don’t already have one. That’s in addition to an extractor hood. Think low level constant.
Also is that a vinyl type floor covering in the pictures? If so, is it damp underneath? If it’s trapping moisture, best that it goes.

2nd to cubists point I’d definitely be looking at that outside ground level if you can. If you can add a trench of some description (look up zebcolm trench) you’re now allowing the outside surface of the wall to breathe a little easier and another route for moisture to exit.

3rd and most invasive would be considering pulling up the kitchen floor either fully or in part. If you establish the concrete floor does in fact have a dpc membrane (this will likely mean no damp between the concrete and a vinyl floor as the dpc serves as the vapour barrier) many have got away with simply taking up the concrete around the edges of the room by a few inches.
The dpc pushes the moisture into the walls so by cutting this back, breaking this bridge and then filling in with a breathable lime product you may find this resolves the situation without going through the pain of fully lifting the slab.

At this point however I would say to consider looking at things holistically. If the rest of your floors are still suspended it’s likely that originally air was able to flow from front to back of the house. Do you still have functional vents at the front?
The concrete kitchen floor may now be compromising airflow under the rest of your floors, introducing damp problems there too so worth bearing this in mind because potentially, going back to suspended in the kitchen could resolve damp problems for the entire property.

Apologies that was a lot of speel but hope that gives you some things to think about. The answers are never straightforward (or cheap!!) with period properties I’m afraid!

 

[Adam-78]

I will do my best to give tips on how to fix but not quick or straightforward I’m afraid.
As I often say in other similar threads, damp can be tackled on multiple fronts. Choose the one you’re most comfortable with first as doing that one thing will help but may not cure alone. Still, to go one thing at a time is less invasive and may help you reach an equilibrium where you’ve not eradicated the damp completely but you’ve got to a point you can manage the moisture away without too much pain if that makes sense.

Step 1 I would say is letting the moisture have a route of escape. Plaster falling off the walls is a sign it’s doing just that….trying to escape. If you can remove the gypsum back to the brick indoors the moisture can evaporate.

It’s really important that you have sufficient airflow particularly as it’s a kitchen meaning it’s already a heavy moisture producing room. Windows can be enough in some cases but you need to think about air movement across the room so you may need to consider some sort of extractor in your kitchen if you don’t already have one. That’s in addition to an extractor hood. Think low level constant.
Also is that a vinyl type floor covering in the pictures? If so, is it damp underneath? If it’s trapping moisture, best that it goes.

2nd to cubists point I’d definitely be looking at that outside ground level if you can. If you can add a trench of some description (look up zebcolm trench) you’re now allowing the outside surface of the wall to breathe a little easier and another route for moisture to exit.

3rd and most invasive would be considering pulling up the kitchen floor either fully or in part. If you establish the concrete floor does in fact have a dpc membrane (this will likely mean no damp between the concrete and a vinyl floor as the dpc serves as the vapour barrier) many have got away with simply taking up the concrete around the edges of the room by a few inches.
The dpc pushes the moisture into the walls so by cutting this back, breaking this bridge and then filling in with a breathable lime product you may find this resolves the situation without going through the pain of fully lifting the slab.

At this point however I would say to consider looking at things holistically. If the rest of your floors are still suspended it’s likely that originally air was able to flow from front to back of the house. Do you still have functional vents at the front?
The concrete kitchen floor may now be compromising airflow under the rest of your floors, introducing damp problems there too so worth bearing this in mind because potentially, going back to suspended in the kitchen could resolve damp problems for the entire property.

Apologies that was a lot of speel but hope that gives you some things to think about. The answers are never straightforward (or cheap!!) with period properties I’m afraid!

Thanks for the info. The concrete floor appear to be the original floor so there are no vents there. There are joist ends that sit inside the brick walls that surround this kitchen floor e.g. a joist that runs from the passage toward the kitchen. The ends of this joist are rotting with what appear to creamy mould or calcium deposit around it. See pic.The flooring is indeed vinyl but the bitumen coating over the concrete appears to be blocking any moisture. If I were to dig out the concrete around the edges how deep down do I dig it?

 

[DaveG]

Do you have a floor plan? Something from Rightmove would be perfect or if not just a rough drawing?
Also a picture of the front of the property.
I’m still skeptical the kitchen floor would have been concrete originally unless it’s a kitchen extension in which case the floor might be “original” as of the 70s or something.
Suspended floors always had ventilation so if there’s no signs of vents at the front of the property either you may well have had ground levels brought up too high at the front as well and if you have no cross flow of air underneath this will cause significant issues to your joists.

Is that radiator pipe in your kitchen coming out of the concrete floor or just running along the wall above the floor?

If the floor was really (1920s) original concrete, possibly limecrete in 1920 (could anyone else confirm?) the only thing I can think of is it maybe once had quarry tiles over the top and they’ve been removed and the bitumen put down in attempt to create a vapour barrier.
Then you may be able to just get the bitumen up to allow vapour through the floor but I’m still unsure for now whether that floor is definitely original without a bit more of a visual layout of the house

 

[stuart45]

If the floor was really (1920s) original concrete, possibly limecrete in 1920 (could anyone else confirm?)

I've worked on quite a few 20's/30's properties that had concrete floors in the kitchen. I'm sure some were original, but I know that on some houses with timber floors they had rotted first for obvious reasons and had only the kitchen floor replaced with concrete.
I don't think limecrete was popular around that time. Concrete with OPC was often used for foundations, floors etc. Even earlier than that it was popular. OPC mortar wasn't used because it was virtually unworkable for bricklaying.

 

[Stevers]

Mass OPC concrete (and even cement mortars (as used very successfully in the Thames Embankment sewer tunnels) were in use from the 1860s. Various hydraulic cements not dissimilar to OPC were in use prior to the widespread adoption of true OPC. First use of reinforced concrete (and Ferroconcrete) was in the 1900s. Just because it was available didn't mean that it was used, but OPC concrete would undoubtedly have been adopted for floors ahead of for mortars and renders.

 

[Adam-78]

Do you have a floor plan? Something from Rightmove would be perfect or if not just a rough drawing?
Also a picture of the front of the property.
I’m still skeptical the kitchen floor would have been concrete originally unless it’s a kitchen extension in which case the floor might be “original” as of the 70s or something.
Suspended floors always had ventilation so if there’s no signs of vents at the front of the property either you may well have had ground levels brought up too high at the front as well and if you have no cross flow of air underneath this will cause significant issues to your joists.

Is that radiator pipe in your kitchen coming out of the concrete floor or just running along the wall above the floor?

If the floor was really (1920s) original concrete, possibly limecrete in 1920 (could anyone else confirm?) the only thing I can think of is it maybe once had quarry tiles over the top and they’ve been removed and the bitumen put down in attempt to create a vapour barrier.
Then you may be able to just get the bitumen up to allow vapour through the floor but I’m still unsure for now whether that floor is definitely original without a bit more of a visual layout of the house

I've attached a floor plan and some more pics. Affected walls are the ones with the dotted red lines in the floor plan. The diagonal shaded lines in the plan is where the new extension the kitchen is.

Some of the concrete under the sink which is part of the original kitchen was all broken up which I've dug out as you can see in the pic. The bitumen layer on top of the concrete is around 15mm thick with a concrete slab underneath of around 30mm thick. The ground underneath is very moist and soft to the extent in areas i can easily poke a screwdriver in. I think the bitumen layer was added when the extension was built as none of it is present under the cabinet beneath the kitchen sink oddly. The dpc line is on the course of wet brick you can see where i've dug out the concrete.

On the wall where I've removed the skirting which was the original area of concern and is an internal wall the gypsum plaster came right down to the concrete floor which I've cut back now. When I look around both these walls that I've dotted in red on the floor plan, at the subfloor level there doesn't appear to be any signs of any ventilation gaps in these walls which you'd expect if it was previously of suspended timber so I'm not sure if it ever was of timber construction? Looking outside, at the gable end wall section of the kitchen there doesn't appear to be any subfloor vents either, which are present for the suspended section of the same wall i.e. the hallway section. Obviously cannot check the front as the new kitchen extension has been built on that end.

The dpc layer on these internal walls appears to be one course below the joist pockets. Seen as the concrete floor comes level to the top of the joist in the hallway and lounge/diner room it baffles me that the joist ends were fitted this way without any dpc material covering the ends? The concrete against these internal walls is therefore breaching the dpc i suspect and with the bitumen layer on top, all that moisture under the concrete is being pushed sideways into the walls.