Advice on damp in a Victorian terrace with concrete floor

[Yammer94]

Hi,

looking for some advice on how to handle a bit of damp in our victorian terrace. We noticed it after finally removing wallpaper to paint after 5 years. Its a bit cold and you can see some water marks upto 50cm up walls all round the house. Its not mouldy or anything hence I don't think its bad. We have wall vents and trickle vents un double glazed windows.

I got builders to try and fit telescopic vents like all our neighbour's, only for them to find We have a concrete slab floor! Looks like put in the last 10 years maybe. There was evidence of slate damp roof course, but couldn't see how intact it was everywhere. The wall apparently felt moist inside. There is a meter ish high render on the front.
We were going to have a french gulley put in at the front as the tiny front is covered in paving which is probably too high.

But now i am nervous that there is no point doing a french gulley and it may impact foundations. Also considered taking down the bad render, but worried about brick damage. Also builder mentioned concerns about finding dodgy stuff when he digs for the gulley given the cracks in the render and window sill (ie should I worry about subsidence?)
His solution is to do a bit of chemical injection damp proofing and leave it at that.

Has anyone got any advice?

Thanks

join our old house uk Facebook group. Basically lime render it x

NO to a chemical DPC.

yes, French drain and get the render off. Let the wall dry out then reassess.

I know someone who had damp in their Victorian house because the concreted over path to the front door was covering the original damp course. They dug up the path, replaced it with gravel that was lower down, and the house dried out! Get your paving lifted as a first move and see what happens.

What plaster is on the inside? Is it pink modern stuff or white/grey lime plaster? If its modern, it will need to come off to dry the wall out. I also recommend taking off the render outside so you can see where the damp proof course is.

Did you have or see any problems before taking the wallpaper off?

My house is like this, though 1920s. All I can say is, don't expect a damp proof injection course to work - we had this just before moving in and 3 years later had problems.

Thanks everyone.

If money, time and finding skilled trades wasnt an issue, I reckon we would take off the render, strip out the gypsum plaster all round the ground floor, put in a french gulley, let it all dry ou for a few months, then get the brick repairedworh lime repointing, lime plaster inside the house, and if needed lime render to replace the old render.

Even if we did all that, I would still be nervous that we take off the render and find evidence of subsidence which would need further repair, an insurance claim and probable chat with our mortgage provider.

Given our damp issue seems mild, I feel like i dont want to risk finding subsidence. As an early victorian house in london i'd be surprised if we didn't find some ecen historic cases.

Agreed that chemical injections dont really seem worth it, and even the builder said its 50/50 if it will do much.

I guess the minimum thing possibly worth doing is a french gulley then. There is a concrete path which ideally we would take up that I hadn't considered before.

The cracks to the render look to be surrounded by damp and blown render rather than subsidence. Although it could have blown after being cracked by subsidence. Without removing the render you won't know. Even if it IS subsidence, it's better to find out and deal with it than to ignore it!

There looks like thenre is a crack in the window cill too though and that might point towards movement.
London houses often have lots of small hairline cracks in brcause rhey are built on clay which swells and shrinks at the weather gets wet in winter and then dries out in summer.
I agree with {mention:PragmaticIsh}@PragmaticIsh its probably better to know. Those cracks will get picked up on a survey if you sell anyway.
I would get the render taken off and i like your plan about the french drains.