Damp on external and party wall

[Doug789654]

Hi All

I posted about this issue at the start of the year (here), but was unable to sort the issue as family circumstances forced me to make the room usable again. Anyway, now is the time to sort it out...

There is damp in the alcove to the side of the fireplace (on the party wall) and on the external wall on my 1890 mid terrace house.

There has previously been damp proofing work around the whole of the back on the house, in 1994 - this location is the only area that is now affected. This work consisted of:

1. An 'injection mortar' being injected into the masonry from the inside. As in this corner the outside floor level is approximately the same as the internal and also the neighbours floor level is a course of bricks higher this was done at 150 mm above floor level.
2. The walls below the new dpc were painted with a tanking solution.
3. The walls were then re-plastered with a 'damp proofing specification plaster'.

The damp on the party wall seems to be coming up from the floor. The photos below show the damp plaster (there was lining paper on there):



The damp on the external wall started off reappearing over my hastily painted wall from below/around the socket and expanded outwards (I scrapped off a bit of plaster where it is damaged). The photo below shows this:



Based on the advice I received back in January I was going to knock off the plaster and then re-render the wall. Does this still stand?

I was wondering if I should also tank again the bottom 150 mm?

Other potentially important points:

• Solid floor with a DPM, although this has been bridged at some points, it looks as if it didn't stick up enough and therefore the concrete met the walls.
• Chimney is in use as a flue for a gas fire.
• The work was done by what appears to be a reputable company (specialist, still going today). It is under guarantee but they want money to change the name and then to come and inspect, and I suspect it may be cheaper just to sort it myself.
• The outside wall appears to be damp at a higher level, maybe coming from the garden wall (photo below and plan of how the garden wall meets my and my neighbours houses). I'm not sure if this could be related or a red herring, or how this could possible be solved?

Thanks in advance for any advice, I really appreciated all the advice last time.

Doug

 

[oldbutnotdead]

Looking at those pics, I'd suspect that the damp on the outside wall isn't 'rising damp'. The vegetation growing out of that outside wall makes me think the soldier course on top isn't working as a cap all that effectively- have a prod at the mortar in the wall, see if it is all crumbly and knackered. Also the green tinge to your house end wall looks suspect- any guttering issues? Even a persistent drip from a leaking joint can blow the plaster eventually. If your roof is original you may be getting rainfall dropping behind the gutter. If your roof isn't original, the felt (where it drops into the gutter) may have perished causing similar problems

Remedies (well things to try anyway)- if the mortar on that outside wall is knackered then lift off the top course, clean up the bed, mortar some slates in (protruding by 20mm or so as a drip edge) then put the top course back on top. That'll stop that wall getting saturated (which I think is where your damp is coming from- water has to go somewhere)

If the mortar isn't knackered then just mortar some slates on the top of it (or if you want to be lazy, get a roll of Flashband and stick that on the top of it).

It'll take about 6 months for the wall to dry out once you've sorted the water source.

 

[Doug789654]

Thanks for your reply Oldbutnotdead.

Looking at those pics, I'd suspect that the damp on the outside wall isn't 'rising damp'. The vegetation growing out of that outside wall makes me think the soldier course on top isn't working as a cap all that effectively- have a prod at the mortar in the wall, see if it is all crumbly and knackered.

It does look like that to me as well. How can I prevent the water coming from the garden wall into the house wall? There doesn't really seem to be a way of isolating the wall as it goes straight into the side of my neighbours house.

Also the green tinge to your house end wall looks suspect- any guttering issues? Even a persistent drip from a leaking joint can blow the plaster eventually. If your roof is original you may be getting rainfall dropping behind the gutter. If your roof isn't original, the felt (where it drops into the gutter) may have perished causing similar problems.

I've looked at this already and there is no leaking from my or my neighbours gutters. The roof was replaced approximately 5 years ago.

If the mortar isn't knackered then just mortar some slates on the top of it (or if you want to be lazy, get a roll of Flashband and stick that on the top of it).

The mortar in-between the top bricks seems sound. I will try to waterproof the top of the wall to prevent water getting in.

Thanks a lot for your help.

 

[Mr Chibs]

Just a thought...

On your side, how many courses of bricks are below the damp course to concrete ground?
You should have the ground level, then two brick courses (min) then a damp proof course.

 

[Doug789654]

Just a thought...

On your side, how many courses of bricks are below the damp course to concrete ground?
You should have the ground level, then two brick courses (min) then a damp proof course.

It was injected from the inside so I am not exactly sure, but the specification said 150 mm above ground level.

At the highest ground level point (this corner where the issue is) the bottom course is half covered by concrete, so 150 mm would be above the first entirely visible course.

If it was injected at this level throughout (which I believe it was) this would make the majority of it 2 or 2.5 courses above ground level.

Thanks

Doug

 

[oldbutnotdead]

Have a look over the top of that outside wall & see what's going on on the other side. Splashy drains, big rainwater butt with no overflow pipe, a flower bed?

 

[Doug789654]

Have a look over the top of that outside wall & see what's going on on the other side.

Wall goes straight down to the ground there. You can see from the photo belowy neighbours window is right next to the window so anything there would block the window.



The garden wall seems OK in my non-expert opinion apart from where it meets the damp looking patch on the house. There is a gap where mortar has fallen or been removed higher up the wall (photo below). I'm not sure if that's been done deliberately to isolate the garden wall and house wall, although at that point the garden wall is actually the side of my neighbours house. The face of the party wall is flush with the garden wall so it kind of looks as if my house was built first and then the neighbours house and the garden wall was kind of wrapped in to it, if that makes sense.



We've had about 12 hours solid rain here so everything in the photo looks wet and horrible.

Don't know if any of these ramblings are helpful/relevant...

Thanks for your help so far.

Doug

 

[oldbutnotdead]

That wall does look better than your first pics suggested . I'd still be tempted to put some flashband or something like on top of the first 6' (as it joins the houses- very boring waiting 6 months for improvement I know but nothing else is leaping out.