I've been trying to get to the bottom of this problem for years - and hoping someone might be able to throw some light.
We have a damp /stained patch about 1m sq in an upstairs bedroom that starts just above the skirting. Its a solid external wall with painted pebble dash rendering externally. I figured possible cuplrits are:
1) Flashing where garage flat roof joins the same exetrnal wall at about the right height. However the patch is random in shape and not consistent with position or run of flashing.
2) External boiler flue chimney. This is not used and is now open at the top (although not open to weather) and capped at the bottom (in kitchen). Its position does overlap some of the damp / stains but again does not follow a consistent position. I am pretty certain the flue is dry as there is no evidence of damp where it is capped at the bottom.
3) Moisture trapped behind the external render.
3) Ventilation issues.
I have attached a rough sketch.
4 years ago the problem was mostly at the top in the corner of the room so I was blaming leaking roof / gutter / flue chimney flashing. I removed chimney & extended tiles, checked gutters etc. Not the slightest bit of difference (although it didnt seem to get worse after rain anyway).
So I hacked the internal render & plaster back to the brickwork and applied a solution to neutralise possible salts resulting from flue. Waited 6 months. Had wall re rendered (with sand & cement & waterproof agent) & plastered.
Top corner is now dry - and problem has now moved to lower area as per diagram.
I have used stain blockers of every type and they just bubble up & stain comes right through.
I am left with a few possible next steps.
Remove & replace external pebbledash render in case damp trapped behind - but reluctant as no apparent damp source...
Put airbrick in redundant flue in case condensation tracking into wall - but frankly as long shot in my view.
I'd appreciate any thoughts!
We have a damp /stained patch about 1m sq in an upstairs bedroom that starts just above the skirting. Its a solid external wall with painted pebble dash rendering externally. I figured possible cuplrits are:
1) Flashing where garage flat roof joins the same exetrnal wall at about the right height. However the patch is random in shape and not consistent with position or run of flashing.
2) External boiler flue chimney. This is not used and is now open at the top (although not open to weather) and capped at the bottom (in kitchen). Its position does overlap some of the damp / stains but again does not follow a consistent position. I am pretty certain the flue is dry as there is no evidence of damp where it is capped at the bottom.
3) Moisture trapped behind the external render.
3) Ventilation issues.
I have attached a rough sketch.
4 years ago the problem was mostly at the top in the corner of the room so I was blaming leaking roof / gutter / flue chimney flashing. I removed chimney & extended tiles, checked gutters etc. Not the slightest bit of difference (although it didnt seem to get worse after rain anyway).
So I hacked the internal render & plaster back to the brickwork and applied a solution to neutralise possible salts resulting from flue. Waited 6 months. Had wall re rendered (with sand & cement & waterproof agent) & plastered.
Top corner is now dry - and problem has now moved to lower area as per diagram.
I have used stain blockers of every type and they just bubble up & stain comes right through.
I am left with a few possible next steps.
Remove & replace external pebbledash render in case damp trapped behind - but reluctant as no apparent damp source...
Put airbrick in redundant flue in case condensation tracking into wall - but frankly as long shot in my view.
I'd appreciate any thoughts!