Damp on internal walls around concrete floor

[Rmgcook]

Hi,

Newbie to this forum so hello everyone!

I’m hoping some people with experience of damp may be able to offer some thoughts on what could be causing a damp problem I have, and possible remediation. I’m not expecting a diagnosis as I appreciate it’ll need investigating, but welcome some ideas as to possible causes.

We live in a 1920 cinder block built and rendered semi. The room with the damp problem used to be the kitchen until we moved it a few years ago.

In one corner of the room is a small area of concrete floor foor, I’ve no idea why there is concrete, the rest of the room has been boarded out with chipboard.

The area around the concrete floor is damp - the carpet has gone damp and some of the paint has flaked off the wall. Both the walls in the photo are internal, the right one is a dividing wall between my house and my neighbour, the opposite side of the far wall is our lounge.

There is no other damp in the room or house and the damp finishes before the floor turns into chipboard.

I’ve read that concrete floors can soak up moisture but I’ve no idea where from, nor why this corner of the room is concrete in the first place. As far as I know there wasn’t a fire in that location, the chimneys are no where near that location.

Any thoughts welcome, I appreciate I’ll need to get someone to look at it but I’m just interested to know if there might be any obvious cause / remediation.

Thanks in advance
Robin

[sammy.se]

What is the floor structure next to the concrete? Is it a timber floor, i.e. joists and floor boards with a void underneath?

I suspect the concrete block is a) acting as a cold bridge, attracting condensation and b) is bridging the DPC on the wall. Can you tell us more about the room, and maybe some more pics?

[Rmgcook]

Hi - thanks for your reply.

Not easy taking a pic I’m afraid, its a fairly small room, around 10’x6’, and is now used for our sons playroom hence the mess in the photo!!

Yes the rest of the flooring consists of timber joists and chipboard, with a void below. The concrete patch is basically under the sofa in the photo, and it stops around 2 feet before the right hand external wall and is probably as deep as the sofa itself.

The far wall is a dividing wall with my neighbour and the left hand wall is an inner wall with our lounge on the opposite side.

Any obvious reasons why there would be a concrete area in the first place and what could possible remediation? I think the concrete is certainly contributing to the problem.

I can’t really take a good photo of the area without emptying the room!!

[sammy.se]

Hi,

it's hard to say why there might be concrete there: could it have been a woodburner or aga at somepoint, and needed a concrete base? I'm not sure.

As you can imagine, it's hard to diagnose further without getting under the floor, but here are the things you should check as a next step:

Are there any pipes in the vicinity? If they are leaking, or are cold and water is condensing on them, the resultant moisture/condensation will get into the air underneath the subfloor and condense on the concrete.
Are any pipes in direct contact with the concrete, and are maybe leaking onto it?
Do you have sufficient ventilation under the room - you mention the kitchen was moved out - was this to a new extension that may have blocked some vents and reduced airflow underneath? Are the rest of your air bricks/vents clear?
From outside the house, can you see a visible damp proof course in the brick work, a few inches or a foot above ground level - it would look like a black line (bitumen or slate). Is the concrete floor higher than this?

It's a hassle diagnosing and solving damp problems - but you may need to look under the floor to get a better idea of what's going on here...

[Rmgcook]

Thanks for your reply Sammy - very helpful and it's given me a few ideas.

At some point there was a cold water pipe which ran past the concrete floor and to the back of my house, feeding an outside tap. The tap has long since been removed during reconfiguration of the house, but I'm not sure what was left behind underneath the old kitchen floor - I probably need to pull the boards up and take a look. There is a stop tap in the same room but as far as I'm aware, the water feed comes from the opposite direction and doesn't run past the concrete floor.

There is an air brick into the floor cavity space but I have noticed that there aren't many air bricks around the house. I'll take a look at how well ventilated it seems.

As for DPC it's impossible to tell - the house is fully rendered down to the ground, all of the houses on my street are the same, so if it every had DPC it would have been a long time ago.

I think the next step is for me to pull some boards up one weekend and take a look. The condensation suggestion sounds plausible given that it was a kitchen and there are water pipes nearby albeit I don't think they run past the concrete section.

I was considering trying some epoxy DPM but I'll investigate the cause before I do that.

[sammy.se]

Sounds like a good next step for investigation.

I would hold off on any epoxy DPM as this will simply mask the problem and not solve it, and It may continue to spread and lead to rot over the years...

[Rmgcook]

I've pulled a couple of boards up today but I'm still none the wiser.

I've attached a few phots.

Photo 1 is from my lounge (opposite side to the room with the damp floor), there are some pipes under the floor and there is one (photo 3) which appears to go through the wall into the room with the damp concrete floor. However, I am pretty certain that the opposite side of this pipe was cut off as this pipe used to feed an outside cold water tap, and the pipe originally went over the top of the concrete floor to the stop tap, so has since been removed.

Photo 4 shows the concrete area with damp along the floor adjoining left and far walls. Photo 5 shows the right hand side of this - it's a brick platform with thin concrete screed top.

I took a video of the the long edge of the concrete platform but I can't post it - there are no water pipes around the concrete / brick structure through. The only pipe is on the opposite wall i the lounge, which does 'look' like it goes into the wall but I am certain it was cut off and a feed taken directly from the water tank to the outside tap instead.

It seems pretty damp to with condensation underneath this area but no obvious signs of any leaking.

Still no sure what remediation would be!!

[sammy.se]

Thanks for the photos.

Do the pipes feel cold, and do they have condensation drops on them? I can't tell from the pictures. It could be that the end of the pipe was cut off and capped in the next room, but there might still be water in it?

Also, on the first picture, I can see two electrical cables going up into the skirting board. Behind them, I think I can see some slate between the bricks, about 1 brick below the skirting board - can you confirm, or am I imagining it? Is there any sign of a DPC (Slate or black bitumen paint) in the brickwork you can see underneath?

Finally - can you feel a draught under there, and is there a 'line of sight' to any vents? Trying to determine what kind of airflow you have under there...

[Ken010]

What could be happening is that the concrete slab is suspended and resting on the perimeter of bricks, all 4 sides, even bricks on the inner surface of both walls?

There does not appear to be a DPC incorporated within the supporting brick. Ground water is causing the dampness on any side of the supporting brick, Not exposed to the natural under floor ventilation, hence the two sides exposed to this air flow appear "dry" but the areas with no ventilation, are able to hold the dampness emanating from the ground.

As to why is that lump of concrete there? possibility it was the base for a Coal Cellar? or base of a Larder, in that case there is a possibility of a couple of now infilled external air bricks on the outside wall???

Remedy? if the above is correct, remove the concrete and replace with suspended timber floor + joists??

Ken.

[Rmgcook]

Thanks for the photos.

Do the pipes feel cold, and do they have condensation drops on them? I can't tell from the pictures. It could be that the end of the pipe was cut off and capped in the next room, but there might still be water in it?

Also, on the first picture, I can see two electrical cables going up into the skirting board. Behind them, I think I can see some slate between the bricks, about 1 brick below the skirting board - can you confirm, or am I imagining it? Is there any sign of a DPC (Slate or black bitumen paint) in the brickwork you can see underneath?

Finally - can you feel a draught under there, and is there a 'line of sight' to any vents? Trying to determine what kind of airflow you have under there...

Thanks for your reply - I'll need to take another look to check for DPC - I should have done that the first time!

However I know that where the pipe went through the wall that the brick work seems to have been hacked away in quite a rudimental way. The brick base underneath the concrete patch also seems pretty messy, so I'm wondering whether a combination of those things - possibly damaged DPC in wall or maybe no DPC in the brick base under the concrete section, could be causing the issue. The water pipe (which I believe was cut off) did feel cold but there was no obvious sign of condensation on it.

[Rmgcook]

What could be happening is that the concrete slab is suspended and resting on the perimeter of bricks, all 4 sides, even bricks on the inner surface of both walls?

There does not appear to be a DPC incorporated within the supporting brick. Ground water is causing the dampness on any side of the supporting brick, Not exposed to the natural under floor ventilation, hence the two sides exposed to this air flow appear "dry" but the areas with no ventilation, are able to hold the dampness emanating from the ground.

As to why is that lump of concrete there? possibility it was the base for a Coal Cellar? or base of a Larder, in that case there is a possibility of a couple of now infilled external air bricks on the outside wall???

Remedy? if the above is correct, remove the concrete and replace with suspended timber floor + joists??

Ken.

Hi Ken - thanks for your reply. To be honest I was starting to come to that conclusion - the whole floor in this particular room is a bit of a mess. It used to be a very small kitchen until we relocated it, and the already badly chip-boarded floor was patched up even more (ran out of money to do anymore work to the room!).

I think to do a proper job it probably does require the concrete base / brick work to come out and joists putting in. I suspect ventilation is not great as you say so hopefully that would help prevent any future issues.