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Stuart Noble

On 04/11/2012 12:39, wrote:
On Sunday, November 4, 2012 12:17:08 PM UTC, stuart noble wrote:
On 04/11/2012 12:07, wrote:
On Sunday, November 4, 2012 9:50:06 AM UTC, stuart noble wrote:
On 04/11/2012 09:03, wrote:
On Friday, November 2, 2012 9:26:17 PM UTC,
wrote:

The most likely cause is condensation, caused primarily by too high
an interior RH. This type of thing is often misdiagosed as rising
damp, which although it exists, is unusual. The solution is normally
to address interior sources of dampness, eg showers without adequate
ventilation, hob cooking on excessively high heat, drying clothes
indoors, unvented gas heating, inadequate ventilation in rooms etc.

The gradual movement of water vapour is from interior to exterior,
since interior RH is higher on average. Thus evaporation of water
from the exterior of the wall is necessary to avoid dampness. You
mentioned a black paint, if you mean bitumen on the exterior then
this can gradually cause damp problems by preventing evaporation.
Painted cement render can occasionally too in walls that are
borderline in terms of how they handle damp, but that's not likely to
apply to a cavity wall. Are you sure they're cavity walls, as
everything you describe is a lot more likely to occur with non-cavity
walls?

Thank you for that glimpse into 1950s Britain before central heating was
the norm

Damp, the subject you can't be bothered to read up on

Where do you get the idea that indoor RH is normally higher than
outdoor? Do you live in a cave?

Well lets see, there's breathing, cooking, bathing, laundry, all put water vapour into the indoor air.

So where does it go? it goes outdoors via ventilation, and to a small extent out through walls.

NT

The warm air indoors is quite able to carry a bit of extra moisture, so
it doesn't go anywhere. In fact, in what I would term a normal household
there is more danger of low rh than high but, if you're not going to
maintain a temperature fit for human habitation, then there won't be
much difference between inside and out. No way to live though