Damp patches on external cavity wall

[sparkykink]

Hi,
I have damp patches on an external wall, however no sign of dampness on the inside wall.
I'm wondering if the damp course may have failed, however this is the back elevation of the bungalow which doesn't get battered by the weather and all other elevations are ok.
We do have cavity wall insulation, the old polystyrene type (not loose balls) which was installed about 18 years ago before we moved in.
I've only noticed it during the last year or so, and am reluctant to get involved with companies / salesmen etc before having an idea what may be the cause.
I'm a retired electrician, so I do have a fair grasp of general building methods etc.

Any advice would be greatly appreciated.

Thanks,

Dave

 

[Ivor Windybottom]

Was this a one-off freak event after rain had blown from that direction?

If so don't worry at all.

I can see that the path is wet but drying out, so presumably the rain was a little time ago.

 

[sparkykink]

Hi, and thanks for the reply.
No, this photo was taken today, and it's just been raining (slightly) off and on here for the last day or so, and dry for the past week, so there's been no splashing from the path.
As you can see from the path, the rain doesn't drive into the direction of the wall so it's dry under the soffit overhang which being a bungalow is just over the window and protrudes about 450mm. It would need to be fairly horizontal to make much of an impression on the wall.
BTW there's no chance of leakage from inside as all heating pipes are under the floor and the boiler hasn't lost pressure.
It's very strange that it seems to be creeping along the outside brickwork, though dry as a bone inside the house.

 

[Ivor Windybottom]

Honestly it just looks like a one-off freak event after some wind-driven rain, I've seen similar on ours after rain. Keep an eye on it, does it look like that all the time?

 

[stuart45]

It takes longer for the heat from inside to help dry out the outer skin with CWI installed.

 

[sparkykink]

Honestly it just looks like a one-off freak event after some wind-driven rain, I've seen similar on ours after rain. Keep an eye on it, does it look like that all the time?

I first noticed it last year around August, it was much a smaller patch then, just above the third airbrick from the left.

 

[sparkykink]

It takes longer for the heat from inside to help dry out the outer skin with CWI installed.

thanks, I'm a bit concerned it may be tracking along the CWI, but no sign of dampness on the inside walls ?

 

[stuart45]

If it was crossing the cavity you'd probably notice damp inside. If the pointing has worn down a bit and is slightly recessed, that will tend to send more water into the bricks. We have been getting more driving rain in recent years as well.
Also the bottom of the walls inside are usually a bit colder than higher up.
Those types of bricks show up the damp more than darker ones. Flettons are also quite absorbent.

 

[Ivor Windybottom]

Bricks get wet when the rain lands on them!