Small damp patch on bedroom wall.

[gusnchris]

Wall is on a gable end. When plaster was knocked off, wall appeared dry. It was all red brick except for one random stone about half way up quite near the corner. Now replastered, a small damp patch still coming exactly where the stone was, especially when the temperature drops. Any ideas?

 

[malcolm]

I would guess that stone wasn't as dry as the rest of the wall and the damp is condensation. Damp walls have a much poorer U value than dry walls and cold walls will attract condensation from the room.

The fix would be to allow that stone some way to dry out. The best way is to let the walls dry to the outside but cement render and waterproof paint will prevent that. Photos inside and out would help any diagnosis.

 

[gusnchris]

Thanks for your reply. Will look into it and get some photos.

 

[Stevers]

Some stone is very dense and impermeable. The Sarsen standing stones at Avebury (a silicified sandstone) would be an example. Such stone is much prone to 'sweating'.

From Wikipedia:
Sarsen is not an ideal building material, however. William Stukeley wrote that sarsen is "always moist and dewy in winter which proves damp and unwholesome, and rots the furniture".[7][8] In the case of Avebury, the investors who backed a scheme to recycle the stone were bankrupted when the houses they built proved to be unsaleable and also prone to burning down.