On 8 Mar, 16:33, wrote:

Its quite the opposite. What many people dont seem to realise is that
water content in a wall is an equilibrium between water entry and
evaporation. Waterproofing products reduce water entry, but they
reduce water evaporation even more, so the wall gradually ends up
wetter.

Although I'd agree your general point, you can't extend this to, "all
walls will become wetter if their outer face is sealed" without
knowing more about the wall and the weather.

How much water exposure does the wall suffer?

Where does the evaporation take place, inside or outside face?
(mainly an issue for sheds, but it's significant for single-skin rear
wings in Victorian terraces too).

Can you reduce the water exposure on the outer face or top surface by
fixing some other problem, such as guttering or inadequate
waterproofing around the eaves?

We've got a big Victorian pile with a damp problem that's almost
certainly caused by a leaking roof valley. Yet the previous owners
spent money on having a "coating" applied to everything outside. It's
a "coating" rather than mere "paint", because paint doesn't cost over
£11 thousand! No fix, a lot of money, and yes it's probably going to
make that specific problem worse rather than better. However the
coated section of the house (apart from this small area) _is_
distinctly drier inside than the unpainted section to the rear, which
has the same wall construction and is actually more sheltered from the
weather.

I also like the colour, although I wouldn't have spent £11k for it!
8-)

SPAB, and the Scottish equivalent, are largely talking about large-
scale buildings with very thick walls. Their obsession with lime
renders as a panacea works fine on those, but it's not the solution
when you're a cheaply-built fisherman's cottage facing the worst of
the sea's weather.