Damp issue in Victorian basement flat - please help!

3 Jan 2021
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United Kingdom
Not entirely sure where to put this so I hope this is the right place.

Im trying to solve the damp issue in my flat, but it seems everywhere I look there is an alternative method of fixing the issue, and so many rogue (and expensive ways) of just covering it up for it to still be an issue down the line.

My flat is a lower ground flat in a victorian town house built in the 1860s. In the 1987 the wooden floor was taken out and replaced with a concrete slab. I have no idea if the concrete slab has an effective DPM, but both the concrete slab and the outside floor levels are higher than the bottom of the air brick, so presumably bridging the original DPM.

An independent survey recommended that I tank the walls with a cement solution but I have decided that it is absolutely not the way that I would like to go due to the long drying time and the impervious nature of the render. From what I have read it seems to create more issues.

Some companies have recommended putting in a damp proof membrane on the walls which have an air gap behind instead of tanking. This reduces the drying and decorating time which is great, but does it still let the walls 'breath' as they need to in older properties? Will it help solve the damp issue or is it another way of just covering it up?

I'm aware that I need to find the source of the damp, checking for leaking drains or water mains etc, but if I were to do that and lower the ground outside the flat, would I need to remove/replace the concrete floor inside the flat as it's bridging the DMP or would this not be an issue?

I'm banging my head against the wall here as there is so much out there and I only have one shot to do this (currently renovating from scratch)
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lower the ground level outside, so its suitably lower than the air brick.

do you know where the dpc layer is? as its such an old building its not out of the realms of possibilty this has failed.

i assume the gutters and water run off areas are all clear and in good working order.

i also assume its a rising damp issue you are having?

the floor could be causing the issues you are seeing, building work in the 80's especially in old properties was quite questionable, so the cementing of the floor could be a big factor.

the issues you have will not have a silver bullet to fix them, the suggestions you have had are relatively quick and cheap fixes and each could have their own issues.

you say you have 1 shot, so the only real option is to do things properly.

as you are renovating and to put your mind at ease dig down a small section of the floor (only needs to be a 2" area), if you come to a membrane (should only be a few inches down) you know the floor can be left as it is and that not your problem.

that being said, the ventilation of the house may have been reliant on the air flow through the original suspended floor and the concrete slab is stopping this, and so other forms of ventilation will need to be sought.
as you are renovating and to put your mind at ease dig down a small section of the floor (only needs to be a 2" area), if you come to a membrane (should only be a few inches down) you know the floor can be left as it is and that not your problem.

Is it possible to then fix the DPM that I have drilled down to? (assuming the excavation would damage it?
Is it possible to then fix the DPM that I have drilled down to? (assuming the excavation would damage it?

dont drill down,

you dig out a small area, one way is to use an angle grinder set to 25mm, cut a square, and then hammer an dchisel, or sds the square out.

keep chisseling until you find evidence of dpm, if you get to 3 inches and find nothing, then it would be safe to assume it doesnt have one.

should you damage the dpm, its very easy to repair, you can use https://www.toolstation.com/damp-pr...MIoYf50q6H7gIV2t_tCh0y_gsXEAQYASABEgK52PD_BwE
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I've not read all the above but a two pee's worth suggestion would be to remove a length of skirting, and you might see a bit of flopped up DPM - that would save you hacking up any floor.
If the DMP has failed in the walls of the house, or if it is bridged by either the inside or the outside, and I install a chemical DMP what is the best course of action following this?

Would it be best just to remove the plaster and let the wall dry out for a few weeks / months and then plaster over as normal?
The DPM means damp proof membrane - its a wide sheet of plastic that typically goes under a concrete pour.
A DPC means a damp proof course - its a roll of black plastic that goes in walls.
If you are in a basement or semi-basement then installing a low level plastic or chemical DPC is typically useless.

You seem to be a bit overwhelmed with the remedial issues so perhaps post pics on here of the inside and the outside of your flat?
WhatsApp Image 2021-01-07 at 19.20.19.jpeg

Air bricks on front elevation

WhatsApp Image 2021-01-07 at 19.20.18 (1).jpeg

Other side of air bricks. Have been covered with a cement plaster

WhatsApp Image 2021-01-07 at 19.20.18.jpeg
Another picture of the inside wall of the front elevation. Located where another air brick is

WhatsApp Image 2021-01-07 at 19.20.17 (1).jpeg


Wood rot on the left hand party wall in our corridor. This was wet to the touch

WhatsApp Image 2021-01-07 at 19.20.17.jpeg



Screed Floor (turns out it's not concrete)
What's the screed floor on? Is it on insulation?

The outside ground being pretty much to the air brick doesn't really help.

How far up the wall does the damp go?

Is it just in that spot?
Lots of questions you were asked above by sxturbo but still no answers.
According to the pic you are in a ground floor flat.

As above, you have extensive rising damp, and maybe some penetrating damp.
You will have to knock off & replace certain amounts of outside render - maybe all of it but there might be free holder issues.
A certain amount of interior wall plaster will also have to be knocked off, & replaced with lime render.
Skirtings will have to be replaced.
The floor base looks like it could be sand & cement.
Lifting the carpets will expose any damp area's.

FWIW: when you do the inside stuff you could do a new elec first fix by sinking the cables into the wall under metal channel's, and raising the outlet base ht to 450mm.
Sorry to answer a few of the questions in this thread I have missed...

I don't complete on the flat until next month, so I haven't been able to get in and do anything intrusive just yet.

As a result I haven't been able to find the DPC. In the past there has been a concrete render applied to the walls. This has now obviously failed in places and is coming off.

It has been diagnosed as 'rising damp', however the reason i'm posting on a forum to ask peoples advice is that there is so much literature online about how 'rising damp' doesn't exist, or is rarely the cause of an issue like this.

Unfortunately I have no idea if the screen floor is on insulation or not. I was at the flat last night (about 2 degrees outside). I checked the temp of the floor with my hand and it wasn't cold to the touch (the flat is unoccupied and heating isn't on), which i'm hoping is a good sign!

The damp goes up about 1m or so. There is damp on the walls inside the front elevation of the flat, and on the left hand party wall of the flat. The damp report however told us to put in a DPC on all external and party walls!

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