Damp advice

[Cgas]

Hi guys after some advice on damp before I get someone out and pay them the survey fee!
Pictures explain better then words so here goes. We have these marks on the wall on the inside of the house, it started as a mark but when I removed skirting we noticed plaster was completely different shade darker then the other half of the wall.

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The part that looks darker is an outside wall the other side, the part that looks dry further along is where the extension starts on the back of the house (outside pics will explain) the white wall on the right of the first pic is the extension, the tape measure that's on the wall is where the wall inside stops.

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The outside at the back looks like this it's built into a bank so the other side of the wall inside is into the void.

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Here's a few other pics just to help (if it helps).

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Basically what I'm asking is does anyone know what's causing this/how I can fix this myself or is it worth paying someone to carry out the work? Any advice appreciated and if you want any pics info let me know.
After picking some peoples brains a lot have said just repoint the wall outside & cake it in thomsons water seal & try to dry out inside and see if that works & replaster, I have also been told you should not inject the wall as it will do NOTHING if you already have a dpc.

Cheers!

 

[jeds]

So your internal floor level roughly matches the bottom of the external render! What is the plaster undercoat? Looks like browning or bonding? Is the brick wall cavity?

 

[Cgas]

So your internal floor level roughly matches the bottom of the external render! What is the plaster undercoat? Looks like browning or bonding? Is the brick wall cavity?

It's a bonding coat, yeah it's a cavity wall.
Yeah the render u can see in this picture at the bottom of that is where the internal floor level is. Maybe a little higher inside as it's concrete floor
Cheers.

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[jeds]

Take one step at a time. It's unlikely to be rising dampness so I'd rule that out for now. Crap in the cavity could be causing lateral penetration or cold bridging, so I'd check that before doing anything else. Either remove a brick or hire/borrow a borescope. You are looking to see if it is clear and if any insulation is present?

 

[Cgas]

Take one step at a time. It's unlikely to be rising dampness so I'd rule that out for now. Crap in the cavity could be causing lateral penetration or cold bridging, so I'd check that before doing anything else. Either remove a brick or hire/borrow a borescope. You are looking to see if it is clear and if any insulation is present?

Can I ask by crap in the cavity do you mean from the builders doing the work filling it with crap and then when cavity insulation is pumped in it sits around the crap and makes that patch damp? If there is crap in there do I just remove bricks and remove the rubbish?
Thanks.

 

[jeds]

You'll often find snots and debris falling down the cavity and collecting near the bottom or on wall ties or on dpc. If there is rubbish in there it doesn't matter what you do on the outside you'll always have problems so it's best to check and know for certain one way or the other. My guess is you probably have cold bridging and condensation more than actual dampness but there's no point doing the work for that and then finding out is was penetrating dampness after all. Also, if the cavity is clear and suitable you could consider cavity insulation which might be your best option in the end anyway.

 

[Cgas]

You'll often find snots and debris falling down the cavity and collecting near the bottom or on wall ties or on dpc. If there is rubbish in there it doesn't matter what you do on the outside you'll always have problems so it's best to check and know for certain one way or the other. My guess is you probably have cold bridging and condensation more than actual dampness but there's no point doing the work for that and then finding out is was penetrating dampness after all. Also, if the cavity is clear and suitable you could consider cavity insulation which might be your best option in the end anyway.

So if I remove plaster from inside wall and a brick 1 higher then the bottom one to see what's in there will work? We already have cavitys filled as I've drilled a core for the toilet upstairs and loads of stuff in there. Failing the cavity is empty, any ideas on the next stage?
Ta bud, appreciate the help so far!

 

[jeds]

Do that. Take out a brick just above internal floor level, which I assume would be just above dpc, and see what you find. Obviously do it in the dampest area. If you already have cavity fill you are also looking for the distribution of the fill. Any gaps will cause cold spots which will attract condensation.

 

[Cgas]

Do that. Take out a brick just above internal floor level, which I assume would be just above dpc, and see what you find. Obviously do it in the dampest area. If you already have cavity fill you are also looking for the distribution of the fill. Any gaps will cause cold spots which will attract condensation.

It will actually be below the damp course as the internal floor is lower then the concrete steps outside, does this matter if the brick I'm removing is below the damp course I would have to go about a metre up the internal wall to be above the damp course if you understand what I mean.

By this I mean the damp course runs up the concrete stairs outside and follows the steps.

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