| Rising damp is the action of water moving
vertically through porous building material in contact with
the ground. This is brought about by the drying action of
air on the upper surfaces which causes the wall to act like
a wick, drawing water upwards from the ground by capillary
action, which then evaporates from the surface into the atmosphere.
The moisture will continue to rise until it reaches a height
where unless no evaporation is possible, gravity takes over
and pulls it down again.
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Water coming from the soil will have various
dissolved nitrates, chlorides and other salts (called hygroscopic
ground salts) which will be carried upwards into the brickwork
and plaster. As the water evaporates, an increasing amount
of these salts will be deposited in the wall. As ground salts
are easily dissolved they also readily attract moisture from
the atmosphere. This means that even if the rising damp is
cured, the plaster will always be damp or contaminated. For
this reason the plaster is always removed when treating rising
damp. Wood rot in adjacent timbers may often be as a result
of rising damp in a wall.
Rising damp occurs because the building’s damp proof
course (DPC) has broken down or is being bridged by high ground.
A DPC installed during construction will be a physical layer
of an impermeable material. This can consist of slate, bitumen
impregnated felt or plastic, for example. Many older properties
do not have a DPC.
Where appropriate, DWC will install a chemical DPC system
to control the problem.
The chemical DPC is injected into the walls at regular intervals.
There will often be a small level of moisture held in the
substrate due to salt contamination even when rising damp
is controlled. Replastering will replace the salt contaminated
plaster and protect the decorated surface from any residual
moisture held in the wall.
Our experienced surveyors will be able to determine if the
dampness reported is rising damp requiring a chemical DPC
and replastering or if it is dampness due to salts left in
the plaster by an old case of rising damp which just needs
specialist replastering.
Decorating
There is a general rule of thumb
that drying times can be calculated by waiting one month for
every 25mm of wall thickness, however, this is based on an
external wall with 'face brick' only. The presence of external
paints or renders will substantially extend the drying period.
A water thinned coat of matt emulsion paint (not vinyl) can
be applied to the internal face of the external wall when
the new plaster is dry. Normal hairline cracking of the plaster
may occur after re-plastering, this can be rectified by by
any competant decorator.
Efflorescence
After injection has been completed the wall begins to dry
out. It may take many months for a wall to dry out if plastered
to the necessary thickness of 25mm. If a wall has been subjected
to rising dampness for many years it will contain residue
ground salts and dampness.
Whilst drying out, the decorative plaster finish may exhibit
efflorescent salts on its surface. Should the crystals appear
on the surface of the wall, simply brush them away gently
with a soft brush, and allow further time for the wall to
continue drying out before decorating the wall. Efflorescence
is normally seen as a dry, white, fluffy covering on the wall
and should not be confused with fungal growth. It should be
pointed out that although these crystals cause no harm, they
can cause even matt emulsion to delaminate.
Electro Osmotic Damp Proofing
Rising damp in buildings is caused by ground water leeching
into masonry via a process known as “capillary action”.
This is a natural process where the moisture migrates into
the pores of the brickwork, seeking a means of evaporation,
and it will continue to rise until it reaches a height, where,
unless no evaporation is possible, gravity takes over and
pulls it down again. This usually takes place at around 1.2m
or 3-4 feet.
While this moisture is rising, the natural electrical charge
contained within the water molecules change from a positive
charge to a negative one. Back in the 1970s it was discovered
that by introducing a small positive charge into the building,
the rising moisture is attracted back into the ground where
it stays. This means that the walls remain dry and damp free.
This system works in virtually all known types of building
structure, whatever their age, and follows the natural scientific
principle of water movement.
The electro osmotic damp proofing system works by fitting
a special control box with titanium wire, which is bent at
intervals to form anodes; these are then fitted into previously
drilled holes at just above ground level. A very small, regulated
and perfectly safe electrical charge is introduced into the
wall via a small power control unit and then the whole system
is earthed. The fitting of the wire is unobtrusive, using
raked out brickwork joints and once the small drill holes
are filled you are left with an almost perfect finish.
An electro osmotic system is the only remedial damp proof
course that will dry below the level of installation avoiding
timber floor removal and replacement. It repels moisture down
to soil level, below timber joists and bearers even when installed
behind or above the skirting boards. It is relatively quick
to install with minimal drilling, debris, dust or damage to
your internal or external masonry finishes and as there are
no chemicals involved, there are no odours.
The running costs of this system are comparable with the
cost of an electric door bell and the system carries a long
term warranty. The electro osmotic system is regarded as the
easiest, cleanest and safest system to control rising damp.
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