External render / screed absorbing moisture?

[gmtfd]

Hello all

We have some damp issues in our house, and it's been suggested that one reason for this may be that the render / screed (sorry, I don't know which is the correct term) on an external wall is absorbing moisture.

The wall is part of an extension built around 1990, and I believe is made of breeze blocks (another incorrect term?). It is not completely vertical, but slopes inwards slightly from the base. As a result water drips onto the face of the wall from the coping stones on top of the parapet wall above. Looking at it whenever it has rained, obvious damp patches can be seen.

I was wondering if anyone on here has any views about this? In particular I'd like to know what is the proper way of rendering such a wall.

Many thanks for any assistance with this.

Regards

Gareth

 

[ree]

Suggest that you post pics of the wall elevation, and both sides of the parapet. A wall built in 1990 that "slopes inwards" sounds pretty unusual.

Damp stains appearing on a parapet render could be from lack of pointing to the coping, lack of a parapet DPC, penetration from the far side of the parapet, or something else.

 

[ree]

I now see that you have a related enquiry in the Roofing Forum. It would help if you could keep all your similar posts in the one post. Hope you dont mind me saying this.

 

[gmtfd]

Many thanks for your replies ree. I have attached images below (the yellow house is my neighbour's property).

The coping stones have been repointed and the capillary channels on both sides have been restored. However, because the wall slopes inwards, rainwater drips from the coping stones onto the face of the wall. As you can see the damp areas are mainly at the foot of the wall.

Your point about the unlikeliness of a wall built in 1990 sloping inwards is a good one, but believe me, you have no idea how low the standards of builders here in East London are!

I'm sorry if I did the wrong thing by posting in two separate forums - it seemed the most appropriate thing to do because there is no central 'damp issues' forum.

Regards

Gareth

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[tony1851]

This is too vague.
Is there an internal damp problem, or are you just worried about the patches on the external wall face?
If the rendering has not been painted, it will always show damp stains after rainfall; the anti-capillarity groves will not stop the rain from being blown back on to the wall surface.
If you have dampness internally, it could be unrelatd to the stains on the wall.

 

[ree]

The render has to come off back to exposed masonry. There are indications of three large render patches. The application and the render mix'es are not to even a reasonable level.

The coping stones appear to be minor contributors to the general dampness.

Plus, when the masonry is revealed the leaning will be exposed, and why its leaning possibly explained.

The concrete fence post has a damaged rendered corner just behind it -if the render corner bead is rusted, it too might have to come off.
Perhaps all the extension render could do with replacing?

On the same corner, the detailing of lead flashing (its going behind the fascia) and cap sheet and fascia is wrong - should there be a gutter on the fascia?

Why was a parapet built on a non-adjoining flat roof in the first place?

Why not post pics of all the extension elevations, the flat roof, and inside the extension where the wall leans?

 

[gmtfd]

Many thanks for your help Tony.

Is there an internal damp problem, or are you just worried about the patches on the external wall face?

Yes, there's damp internally.

If the rendering has not been painted, it will always show damp stains after rainfall; the anti-capillarity groves will not stop the rain from being blown back on to the wall surface.

That's a good point - I hadn't thought of that.

If you have dampness internally, it could be unrelatd to the stains on the wall.

At the moment there are several possible culprits for the internal damp - the others are an area of brickwork which needs repointing, possible water ingress around a skylight, and a possible leaking pipe. It's proving to be an absolute nightmare establishing what is causing it.

Gareth

 

[tony1851]

As per` ree, the coping stones may well not be the issue - the stains on the render look bad (and it is poor workmanship) - but are probably unrelated to the internal dampness.

You need to establish if the wall has been built with a dpc at the base, and if it is a cavity wall.
Also, is there a dpm under the floor slab (difficult to find without cutting) and is it linked to the dpc?
Could the damp be due to condensation?
You need to be far more specific about the damp problem, and a few internal pics would help.

 

[gmtfd]

The render has to come off back to exposed masonry. There are indications of three large render patches. The application and the render mix'es are not to even a reasonable level.

Perhaps all the extension render could do with replacing?

I was worried that this might be what needs to happen. It just looks like the wall has been done really badly. As my Italian partner says, "They must have done it with their feet".

On the same corner, the detailing of lead flashing (its going behind the fascia) and cap sheet and fascia is wrong - should there be a gutter on the fascia?

There is actually a gutter, but it's not very evident from the picture. However there are certainly numerous other issues to do with the extension (and our house generally), not just the wall.

Why was a parapet built on a non-adjoining flat roof in the first place?

Don't ask me! All I can say is that it seems to be impossible to find a decent builder in this part of the world, I posted a long rant about this elsewhere on the forum recently.

Gareth

 

[ree]

Are you posting, more or less the same OP, on various forums of diynot?
What do the bathroom pics have to do with anything?

 

[ban-all-sheds]

What bathroom pics? They are all of the exterior...

 

[ree]

Bit of a puzzle, i brought up the original exterior pics, and some bathroom pics had been added.