I live in a c. 250 year old detached cottage. The walls are solid stone / rubble c. 1’ thick.
We are experiencing what I believe is rising damp on the inside of what is an external facing wall. It is only on 1 wall (the adjacent wall, that is also external facing, has no signs of damp whatsoever and has been tested with meter – it was bone dry). The damp patch is in a wave running the width of the wall (about 12’) and height of 4’ at its peak, running to c. 1’ at the corner.
The periods of damp are highly intermittent – we have periods where the wall is very dry, and periods where it is wet to the touch. As a general trend it is worse in the evenings than at any other time during day.
We have a “copper wire” DPC installed (this was present when we purchased the house). The green light is on at the base of the unit and there are no other signs of damp on any other wall so can only assume this circuit is still complete and the dpc is working.
We had a surveyor friend round who believes issue is rising damp. The wall we were experiencing the problem had a concrete path running along the outside that was quite a bit higher than the internal floor. He suggested the dpc may be being breached by this path so suggested we dig this up so external floor is same level as internal, which we have done. The damp dried up for a week or so, but has now crept back. This could have been entirely coincidental – as per above, the periods of damp are highly intermittent.
There is a set of pipes running from the boiler into the house at the wall that we are experiencing the damp. It has been suggested a small crack in these pipes could be source of damp, but we were advised the dpc should stop this anyway…
The external is fairly sheltered by an outbuilding, but we have also noticed that the rain does run down the bottom section of the external wall – the “lip” from the pebble-dashed section of the wall doesn’t seem to be fully lifting the water away from the wall base as I assume it is supposed to. Not sure if this is contributing to the issue and could the problem be penetrating damp??
Please help – any advice greatly appreciated!! Not really sure where to go next, but trying to avoid spending too much money as long term plan is to extend the house an ultimately knock down the offending wall anyway!
Many thanks

  • David Bergin FCIOB, AssocRICS, FBEng

    Hello Justin,

    With regards to the issue of damp to your one external wall, if you had got rising damp you would have it on a permanent basis, I doubt that it would disappear just because you removed a pathway. To dry out a wall that is 1′ thick would take more than a week, normally once the issue has been cured brickwork drys out at the rate of 1" per month and that is dependent on weather conditions so you would be talking 12 months. I would think that there is another problem/problems that are affecting the wall, with reading your description it could possibly be ingress of rain water through friable (Powdery) mortar as it disappears so quickly so check the external pointing in the first instance for cracks as rain running down a wall will be sucked in by capillary action.

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