Victorian terrace: Penetrating damp in rendered gable end wall

[alex_s]

My house is a Victorian terrace which was mid terrace until WW2 when it became end of terrace. There is damp in the end wall in both front and rear corners of the house, mostly on the first floor but now also showing at high level on the ground floor in the front corner of the house. The end wall appears to be cement rendered. and all 3 main exterior walls are painted with what I presume is masonry paint.

This photo shows the damp in the front corner of the first floor. The visibly damp part next to the window starts about 180cm from the floor. The whole wall in the alcove, both front and end walls of the house, are very damp below about 2m. The visible damp patch by the window is connected to the damp patch in the alcove - so it's feasible the source is entirely from the end wall. I guess it's also possible there is an issue with the window, but I can't see anything from visual inspection of the frame and where it meets the wall outside.


I had a damp surveyor round earlier in the year. He suggested that the water was getting in through the top of the parapet wall and getting trapped by the render and paint on the outside of the house, so in August I had the parapet walls capped with coping. Since then the damp in the first floor has got worse and now it appears in the ground floor too. While it's been a damp autumn and the surveyor did say it might take a few months to dry out once capped, it is getting worse rather than better so I want to find out what's going really going on.

I can get in the loft with my damp mete (admittedly Amazon cheapo, but it can tell the difference between my damp and dry walls): it reads low on the inside of the end wall at that height. Regrettably I don't have records for what this read before the works were carried out, so it's possible the top of the wall was never the problem.

Photo below (taken during capping works) shows the front half of the end wall (rear half is similar, with buttress to mid-first floor and similar arrangement of the old chimney stack of the former next door house). The cable for the satellite dish enters down at ground floor level so is not a suspect for the water ingress. The wall seems to be about 26cm deep, so although will have been built as a party wall which I understand means will likely have had less care and attention from the Victorian builders, is a full 9" wall. While they were up there capping the wall, they did fill the visible cracks in the render and repaint in places.

Having done some more research, it seems like the problem may be that water is getting into cracks in the cement render and getting stuck behind it, and the "correct" solution is to hack it all off and get it re-rendered in lime render. That sounds expensive and I'd hate to do that then find it wasn't the problem either.

What investigations can I do to test this theory? Can anyone please recommend a professional who will be able to guide the process and conduct investigations? And finally, if I do have to re-render the wall, what's the best way to find someone good to do it? Is it a job for any decent plasterer/builder, or does it require specialist skills. I'm in NW London.

Thanks in advance for any advice.

Alex

 

[a twig]

If my understanding of your photos are correct then my suspicions would focus on the downpipe from the gutter, making sure it isn’t block and is draining away freely.

In the place I am currently in I bad damp on the first floor due to a completely blocked down pipe which would back up until it met the join about 2/3rds of the way up and then force its way out, pouring down the walls and soaking them.

Unblocking the gutter completely resolved the issue

EDIT: it also looks like the gutter doesn’t run all the way up to the end of the roof? Might be my eyes though

 

[a twig]

Always worth going outside during a heavy rainstorm and actually trying to see what is going on, use binoculars if access is difficult. Look where the water is overflowing, splashing, sheeting down walls etc.

Yes you look like a wally when doing it (my wife finds it hilarious when I am running around with a brolly and a torch in the rain) but it has definitely helped me identify a multitude of issues

Often lime plaster is only really helpful when mitigating unresolvable issues on the ground floor - I and many others on here have done lime in the ground floor but been able to “get away” with gypsum on floors above that.

If there are salts etc that have come through then at some point the old gypsum will have to come off as it will attract moisture, given the age of the property you might get lucky and find original lime underneath and only a gypsum skim, in which case the saturated gypsum tends to part company with the lime quite easily and you may get away with just patching the original lime then using a lining paper

 

[malcolm]

Water will tend to cause damp at the point where it gets in from outside. It won't travel far.

I had trouble with painted bricks but it looks like your mortar is exposed and if it's lime it should be OK. Maybe a photo of the corner with some of the front might help with ideas.

 

[alex_s]

Thanks both for your replies.

I think the gutter/drain is ok - no obvious problems in heavy rain, but will certainly keep an eye on that. It does reach the roofline! Also, the internal damp is at both front and rear corners of the house, and there isn't a gutter downpipe at the rear.

I'm confused by your comments about the lime and lining paper, are you talking about the inside or the outside?

Here's another photo of the front taken today, and I've drawn on in red the rough area where the damp meter reads 100% on the internal walls. I've deliberately not closed the top right corner of the red area as I can't easily tell whether that 'shoulder' of the chimney is above or below where the damp starts. Although it is rather suspicious that it's close, maybe water is getting in where the chimney shoulder meets the wall? I've also included a detail of how the rendered side meets the brick front.

 

[malcolm]

I see what you mean about the gap between the bricks and render. Water is going to find it's way in there and won't be able to evaporate away as everything on the outside is waterproof.

That gap wants filling. With everything else being waterproof a mastic would probably be best.

 

[alex_s]

I see what you mean about the gap between the bricks and render. Water is going to find it's way in there and won't be able to evaporate away as everything on the outside is waterproof.

That gap wants filling. With everything else being waterproof a mastic would probably be best.

When you say filling, where do you mean? There isn't actually an open gap at the front there, that's just a shadow. I can imagine there being a seam between the render and and brickwork where the water would travel, but that would cover the whole side of the house and how would we get in behind to fill it?

 

[Stevers]

I'm sceptical about any of the sloping rendered surfaces (chimney flue and those little bits of front and back wall). Their position seems to coincide with where the damp is, and to my mind they should be tiled or slated with flashing and something to shed the water at the bottom.

 

[a twig]

Interestingly enough just popped on here to say the same, there are a few houses round here with similar style external flues at fun angles, and being nosey on my way home tonight i saw that on all of them the sloped surfaces are tiled / slated and dressed into the wall with lead work

 

[alex_s]

Interesting, I remember one of the builders I had quote to put the coping on the top of the parapet walls was very keen on lead work, and recommended using that both for the parapet tops and the sloping parts of the chimney. We didn't think lead would look right on the parapets so we didn't go with him, but maybe he was right about the need to cover those sloping bits. The house behind ours has the same set up (presumably thanks to the same bit of WW2 ordnance!), also with rendered but not tiled/slated/flashed chimney slopes so I might go and ring their doorbell and see if they have similar problems.