Rising damp and heavy breathing

30 Dec 2015
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United Kingdom
Another damp puzzle. Can anyone help solve mystery of intermittent damp on dining room walls.
1930 house, original bitumen damp course in walls and concrete floor slab with parquet laid in bitumen on the floor.
Last few days I sealed myself in the room with sander and set about the floor. 8 hrs later the room is steamed up with all my heavy breathing. No surprises there.
Damp patches appeared above the skirting in blotchy patches. Not a consistent pattern, but on both internal and external walls. Once the room was ventilated the patches started to recede. I'm puzzled why the humidity affected the walls in inconsistent patches? Why just those areas? The walls are original plaster with one layer of paper.
I'm considering painting those areas with a damp seal paint before decorating. Would appreciate your thoughts as don't want to just move the issue somewhere else.
Thanks for your help folks.
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The coldest part of the wall is at the base, hence the condensation. Also if you have cavity walls the cavity might be bridged at the bottom where all the bits of mortar end up.

Yes I agree the possibility on the external walls, but it was just the same in odd blotches on the inside walls too. I wondered about salts in the plaster, but its the original stuff not patched or anything.
Even internal walls will be cold at the base of the wall, especially.
It's condensation, as p of d indicated. You'll probably find that it's worse on external walls, and if you place furniture, etc, close to external walls, you might get signs of mold due to condensation caused by reduced movement of air in those places.
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Thanks for info so far its helpful.
What do you suggest moving forward. Obviously on a day to day the humidity shouldn't be as high. Ideas to stop reoccurance?
Same old response....ventilation.
When you're working out, ventilate the room.
Buy yourself one of these little indoor gyroscope toys and move air around in the room, especially in the dead corners, when you're sitting doing nothing.
Ha ha need translation of the phrase ''sitting doing nothing''!!

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