Treatment options for rising
damp
INJECTED DAMP-PROOF COURSE
Still the most popular system of installing a damp-proof
course and are usually offered by damp-proofing
contractors whose installation is covered under British
Standard (BS 6576:2005- Code of practice for diagnosis
of rising damp in walls of buildings and installation of
chemical damp-proof courses ) and usually comes with
approval through a British Board of Agrément Certificate
BBA ( example- Agrément Certificate 95/3210 for Triject
Chemical Damp-proofing system issued to Triton
Chemicals).
Holes are drilled into the thickness of the wall to
attempt to saturate a zone usually around 75-150mm high
at approximately 150mm above the external ground level
at various centres and depths. A damp-proofing fluid,
usually based on silicons or aluminium stearates, is
then pressure injected into the wall. For a brick to be
an effective damp-proof barrier it needs to be injected
for approximately 20 minutes and therefore to treat an
average sized house effectively it would take at least
two days and as most injecting jobs are finished in
around 3 or 4 hours then there is unlikely to be any
proper water-proofing effect from the damp-proofing
fluid. For more information on injection times please
refer to an article by I'Anson S J & Hoff W D (1990)
Chemical Injection Remedial Treatment for Rising Damp -
II Calculation of Injection Times. Building and
Environment Vol 25 No1 pp 63-70.
This system usually relies on the new waterproof plaster
to hold back any dampness in the walls as most treatment
companies can never be certain that the brickwork being
injected under pressure is totally saturated as this
leads to viscous fingering whereby the damp-proofing
fluid follows the line of least resistance leading to an
ineffective chemical damp-proof course. The
specification of the plaster is usually a dense
sand/cement render which itself will prevent the passage
of moisture onto internal wall surfaces.
Full treatment to an average sized house can easily
exceed £5,000 and it is not just the expense to worry
about but there is usually a lot of disruption
internally with the removal of wallcoverings, skirtings
etc and then all the hassle of re-decorating after
allowing the walls to dry out.
In many cases damp-proofing works are only undertaken as
a part of a mortgage condition to obtain a guarantee
against the recurrence of rising damp.
A more recent innovation in the injected damp course
market is the use of gels and creams which are squeezed
into pre-drilled holes using a large mastic gun. These
materials have only been used for the last 5 years or so
and there is no evidence to indicate whether they are
effective or otherwise but somehow it does not seem
likely that they will be as effective as broken down
physical slate or bitumen damp courses that they are
intended to supersede. They are touted as a quick and
easy way of inserting a damp-proof course but in
practice these materials are hard to use leaving globs
of cream or gel oozing out of the holes and they often
don’t diffuse into the brickwork in high humidity levels
( i.e. when the wall is wet) and even after 2 or 3
months the gel or cream may still not have penetrated
into the brickwork which reduce their damp-proofing
effect
Prior to opting for silane diffusion via cream injection
Peter Cox had a transfusion system of installing a
chemical damp-proof course whereby the siliconate
damp-proofing fluid was gravity-fed through bottles and
tubes placed in drill holes. The damp-proofing fluid
would then diffuse slowly into the wall and saturate the
brickwork filling voids and pores whilst avoiding the
viscous fingering which occurs with pressure injected
damp-proof systems. Currently there is only one
transfusion damp-proofing system available in the UK and
this is a frozen damp-proof course known as Freezteq
whereby frozen sticks of damp-proofing fluid are
inserted into pre-drilled holes. The ice sticks then
melt gradually and the damp-proofing fluid spreads
gradually across the brickwork and provides and
effective damp-proof barrier. The only drawback is that
it can be a time consuming process as after the first
set of sticks has melted the process has to be repeated
2 or three times in order to form an effective
damp-proof course. But according to I'Anson & Hoff the
correct installation of a pressure-injected damp-proof
course would also be time consuming and the Freezteq
damp-proofing system is acknowledged by most scientists
in the remedial treatments industry as being the most
effective form of retro-fit damp-proofing available
today.
There is also another transfusion type damp-proofing
system marketed by Koster Waterproofing which involves
the drilling of holes and then injecting a damp-proofing
resin which as well as being hydrophobic ( i.e water
repellent ) is also a pore blocker and has proven to be
very effective in preventing rising damp. However it can
be time consuming as the injection/ diffusion process
can take up to 48 hours and is more complicated than any
other injected damp-proofing system and the whole
process involves using resin cartridges, suction angle
units and capillary tubes for each drilled hole but the
manufacturers are very confident about it’s
effectiveness in controlling rising damp. For further
information contact Koster Aquatechnic in Dumfries on
01387 270252 or
www.kosterwaterproofing.co.uk
EVAPORATIVE DAMP-PROOF COURSES
Believed to be used as long ago as the 1930s when the
Knapen tube system was used at the Palace of Versailles
and later patented by Royal Doulton after they found
that their ceramic tubes appeared to attract and absorb
moisture.These tubes were heavily marketed in the 1960’s
and 70’s but fell out of favour with the public with the
advent of chemical damp-proofing which could be done at
roughly half the cost. Currently this form of
damp-proofing is only undertaking by one company in the
UK (Hydrotek Wallguard) but their website does not give
a comprehensive explanation of how this damp-proofing
system works.
There is no independent scientific evidence to show that
this form of damp-proofing reduces rising damp but there
does seem to be some evaporative effect just above
ground level which can lead to a slight reduction in
rising damp internally and allow re-decoration without
the need for re-plastering.
A more elaborate system has been developed by Schrijver
Damp Control and Holland Damp Proofing both which are
designed to induce air-flow, condensation and moisture
removal but they seem to be dependent on local wind and
weather conditions, i.e. it depends on which way the
wind blows . Research by the Independent Dutch
Laboratory, TNO (Organisation for Applied Scientific
Research) states that the performance of these
damp-proofing tubes is governed by external
environmental factors such as wind speed, wind
direction, temperature and relative humidity and neither
the Wallguard, Schrijver or similar systems of rising
damp control have been awarded with a British Board of
Agrément Certificate (BBA).
These much maligned damp-proofing systems do have some
evaporative effect and will help walls dry out but so
would the drilling of any 50mm diameter holes at the
base of damp walls and if you are considering using this
form of damp-proofing then please take a moment to look
at the photos below to see how your property would be
irreversibly disfigured at a cost of several thousand
pounds when the same affect could be achieved at a
fraction of the cost by installing extra air bricks or
vents.
The picture on the left shows a semi-detached house in
Malvern, Worcestershire, the row of inserts at the base
of the wall are intended to stop rising damp but this
treatment was probably not needed as the house was built
around 1930 and will have a functioning physical
damp-proof course at the base of all the ground floor
walls. The row of tubes on the first floor were probably
to control condensation dampness but this could have
been achieved easier and cheaper by the installation of
two or three passive dehumidifiers.
The photograph on the right is a terraced house in
Sandycombe Road, Kew, Richmond TW9 3SU with the
damp-proofing works being carried out at first floor
level. Is this to stop rising damp or condensation
dampness?
ELECTRIC DAMP-COURSES
Electro Osmosis as a form of damp-proofing is a system
first discovered in approx 1800 by the physicist Reuss
in an experiment which showed that water could be forced
to flow through porous clay diaphragms when an external
electric field was applied. Flow is initiated by
positive ions and is directed from the anode (positive
anode) to the cathode ( negative electrode) reversing
the polarity of capillary action. In 1930, the Ernst
brothers in Switzerland developed a system of applying
electro-osmosis to drying out foundation walls. Three
Hungarians, Miklos Lipscey, Imre Biczok and Zoltan
Horvath, developed the system in Hungary, Paul Wieden
did so in Austria and Dinu Moraru in Yugoslavia, and it
was introduced in a patented system to Britain by W. J.
Holmes of Rentokil and this system was used between 1962
and 1974 in over 55,000 houses before being superseded
by the ever popular injected damp-proofing systems still
used to this day.
However as the green lobby has grown there has been a
resurgence in the use of electro-osmotic systems as a
chemical free damp-proofing option and they generally
consist of a titanium wire being installed at the base
of the all walls and a small electrical charge applied.
This system still involves a lot of internal disruption
as the wire has to be fitted in mortar joints and all
skirting boards will have to be removed to facilitate
this. As with chemical damp-proofing plaster will have
to be hacked off at least one metre high and then
replaced with a waterproof render. This system may be
chemical free but it is scientifically unproven and it
is also quite expensive and the householder also has the
hassle and mess of plaster being removed and the
replacement of skirting etc after the work has been
completed.
The Building Research Establishment has investigated
electro-osmotic damp-proofing and it has some
reservations about its effectiveness in controlling
rising damp and this form of damp-proofing has never
been awarded a British Board of Agrément Certificate
(BBA).
PHYSICAL DAMP COURSING
The Building Research Establishment, in its Digest 245,
confirms that a physical damp-proof course is the only
completely sure method to cure rising damp but is very
expensive, involving sawing out sections of a mortar bed
and then inserting physical membrane.
Diamond tipped angel grinders are used to cut a section
through the wall, of up to 1m in length. The dpc is then
placed in the slot, bedded on mortar, with spacers
inserted along the section to support the wall and
compress the mortar. This wall is then repointed to
create a finished job that is both neat and tidy, and –
more importantly - effective. After the first section of
wall is finished then the next metre of wall can be
treated. It is a labour intensive and disruptive process
but the work can be guaranteed for 50 years.
The lifespan of a physical damp course is far longer
than any chemical damp-proofing and it creates a total
barrier against rising damp.
ENVIRONMENTAL CONTROL
Physical damp-proof course have been required to be
inserted into all buildings constructed since
approximately 1875. Initially this would have been a
horizontal layer of slates overlapping to form a
continuous barrier at the base of the wall, usually at
the same height of the air bricks and in the 1930's this
was replaced by bitumen which has now given way to the
plastic rolls of damp-proof membrane that can be
purchased from any builders merchants.
Slate damp course are still fairly effective in
controlling dampness and often there is no need for any
replacement damp-proof courses as most cases of 'rising
damp' are in fact usually low-level penetrating dampness
where water is sitting at the base of a wall or the
original damp-proof course has been bridged, both of
which create a 'moisture reservoir' allowing water to be
drawn into the wall by capillary action and this then
appears as rising damp internally.
Instead of installing a chemical damp-proof course it is
usually easier and cheaper to tackle the problem
externally by reducing ground levels or installing
drainage channels to prevent bridging and repairing any
drainage and guttering defects which may be causing
ponding externally. Once these works have been carried
out then the walls will dry out gradually and there is
usually no need to remove plaster internally so as well
as saving money by not having to have damp-proofing work
done then all the mess and disruption of plastering and
re-decorating internally is also avoided.
Even if there is any slight passage of moisture through
the old damp course it rarely causes any problems
internally as the rate of evaporation from the wall
above the damp course is usually greater than the uptake
of moisture below the damp course.
Inadequate sub-floor ventilation is often a cause of
dampness in walls as this tends to cause a build up of
moisture in the floor void which can condense on the
exposed masonry and timbers. Much of the condensate will
be above the damp course and will then migrate upwards
to appear as 'rising damp' internally. The easiest way
to deal with this is to install extra air bricks at the
base of the walls and ensure that there is an adequate
through draught of air to remove moisture from the void,
this will also help to reduce the moisture level of
floor timbers and reduce the risk of decay and
infestation.
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