Can visible mould and damp be good in a house?

Perhaps an odd question to
ask, for how can visible mould and damp be healthy, beneficial or
aesthetically pleasing?

The short answer is that it
cannot, but there is a BUT. This BUT is quite a big one as well.
Being able to see mould and damp at least tells you that there is a
problem. Many houses these days are ‘tarted up’ to sell to
un-supposing buyers who take out minimal structural or condition
surveys. The main way of making a damp house look OK is to ‘dry-line’
it. This effectively places a piece of plasterboard between you and
the damp wall. Lovely.

Knowing that you have damp,
and where it is, can take you on a voyage of discovery, especially
with older solid walled houses. You will discover how these houses
were made and with what materials, it can also tell you how they were
designed to work and how they coped with mould and damp in their long
history. After all people of 100 years ago didn’t want mould and damp
either, so why has your house got it now?

Damp can have several causes
and this article will help you to identify where it might be coming
from, how to deal with it permanently and which materials to use so
that you work with your home rather than against it.

To understand how these
concepts and practices work, we first need to understand how these
old solid walled houses worked originally. In North Wales, like many
other parts of the country, people had to make buildings out of the
local materials, so this meant a great deal of stone and slate was
used to create walls and roofs. To bind it all together they used
lime putty and a local aggregate (stone waste from quarries, sub-soil
etc) The walls were either then left bare, or painted with a limewash
(basically a watered down lime putty). The insides were rendered and
plastered using a lime render (made from lime putty, local aggregates
and some binder – sometimes horse hair, wool etc.) These materials
were put together as a solid wall with dressed stone to the inside
and out and any old rubble through in the middle as packing. These
materials work together really well and they allow moisture to pass
through them (either as a vapour or a liquid). The inside of the
building was drier than than outside as the basic building physics
meant that the water was attracted to the outer parts of the wall
(issues to do with surface area of the wall, internal and external
air pressure, internal temperatures etc.)

So these old houses
basically kept the insides dry by allowing the water to move through
them naturally. Yes they got wet when it rained, but the building
physics and the thickness of the walls allowed this to happen in such
a way that the building coped with it.

So what has gone wrong?

Time, does not stand still,
and over the last few decades these old houses have been ‘improved’
using modern materials and techniques to accommodate new lifestyles.
We now have central heating, better airtightness, inside toilets and
bathrooms, double glazing, cookers and hobs rather than fires and
chimneys and quite often concrete floors and wall renders. We have
also been tempted into creating a modern feel to the house by using
new smooth gypsum plasters and cheap oil derived paints and finishes.

These features have
fundamentally changed the way that old buildings are used and this in
turn has changed the pressure points on them. The materials that we
now commonly use are also placing a new and largely unknown pressure
on the house. The effect has been to radically change the way that
they function as physical structures and this in turn has led to the
mould and damp that we now commonly associate with old properties.

The new bathrooms and
kitchens generate a huge amount of water vapour in the internal
atmosphere. The removal of chimneys and the replacement doors and
windows have radically reduced draughts (this is a good thing of
course), but most importantly the use of cement renders, non
breathing roof and wall insulation and the introduction of solid
concrete floors has sealed the dampness in the house and especially
the walls.

Where once water vapour and
moisture passed through the structure, now it gets trapped behind
impervious render. Where once air wicked away moisture from under the
house, via air-vents under the floor, any rising damp is forced by
the damp proof membranes into the walls (inc. internal walls). To
make matters worse, the cement renders applied to the external walls,
tend to crack over time as they don’t flex like an old lime render.
This lets water in behind the render and then stops it from getting
out again. Where does it go? I think that you know the answer now.

To compound the problem, wet
walls conduct heat better and this causes cold spots to form and this
in turn is the breeding ground for mould. Cool and moist – lovely if
you a mould spore!

So mould and damp can tell
us that there is a problem and also show us where it is. This then
allows us to do something about it. It could be: clearing out blocked
guttering and drains; cracked render; rising damp from the floor;
failed seals around doors and windows …. BUT at least you can then
do something positive about it. If you don’t know that there is a
problem and it goes untreated it can cause structural failure in a
house. Not what you want.

The best remedies are the
old ones. By working with the house and using breathable materials
(lime putty renders, wood fibre insulation, clay plasters, natural
paints etc.) you can reinstate the way that it once worked and let
the house do the hard work of keeping itself dry. If you are looking
to buy a house just bear these things in mind – look out for: ‘blown
render’ on the outside walls (it sounds hollow when you tap it); dry
lined walls (again they sound hollow when tapped); worthless 20 year
damp proof injection guarantees; flaky paint and rotting skirting. If
in doubt buy a cheap damp meter and take along with you (note that
dry lined properties will not appear damp to you or the meter, so a
tap is essential).

If the house is
fundamentally solid, but damp and mouldy, at least you will be going
in with your eyes open and ready for the remedial work ahead.