Civil Engineering Reference
In-Depth Information
somehow float on top of it, and this hasn't
been very successful. Long expanses of
wall laid with cement mortars need to have
joints filled with a flexible material built
into them to control cracking, which is why
you see those ugly vertical joins every few
metres in modern buildings. Victorian walls
were able to run for miles around gardens
and estates if necessary without any such
join because the lime mortar they were
built with did this job itself. Modern houses
are far less durable and won't last several
hundred years as their predecessors did,
partly because of this lack of flexibility. This
is not to mention the other undesirable
effects to do with damp and condensation
that are attributable to the use of cement in
modern housing stock.
can get into the wall and provides pathways
for it to escape naturally back out again.
If we make foundations of non-porous
materials such as stone (though be careful,
as not all stone is non-porous), engineering
brick or recycled foamglass, then any
moisture in the earth cannot travel upwards
through them. There cannot be any rising
damp, which is caused by capillary action
wicking water through tiny spaces in materi-
als. And if we use vapour-permeable mortars
such as lime or clay then any moisture that
does find itself in there will migrate out
through the mortar joints.
Traditionally, a capillary break was used to
prevent the movement of moisture from the
earth into the foundation. This is a layer of
stones all the same size and at least 75mm
(3”) thick, such that water cannot pass up
through them by capillary action, because
the spaces between the stones are too
large for this to happen. In many European
countries this is still the preferred method
of providing a damp-proof course, and it is
becoming more popular again in the UK and
Ireland as we are thinking through some of
the causes of damp and trying to find sus-
tainable solutions for them. Capillary breaks
can be used instead of a plastic damp-proof
course, particularly underneath solid floors.
We know that our old houses were and still
are flexible, because they have changed shape
over time.
So it's really important to build flexibility
into the design of your foundations, and you
can do this by using flexible mortar made of
either lime or clay.
For moisture control, use capillary
breaks and vapour-permeable materials
Moisture in the walls will migrate downwards
very, very slowly, because of gravity, so we
don't want a sheet of plastic catching this
moisture and creating a problem in 20 or 30
years' time. Instead, we want walls to sit on
foundations that allow any moisture to travel
down through them and evaporate harm-
lessly out through the mortar joints.
One of
the main problems with plastic damp-proof
barriers is that they are waterproof!
The design
All walls, whatever they're made of, whether
brick-and-block or straw, will contain mois-
ture because of normal human habitation -
breathing, taking showers, etc. - plus
foundations are in contact with the earth,
which is often wet. So to keep the inside of
our houses healthy and free from damp, we
need to design a foundation and wall system
that takes into account the ways moisture
