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GUIDE
TO THE TREATMENT
OF DAMPNESS
Many homeowners involved in renovation or maintenance
work on older buildings will eventually be confronted with the
most annoying and persistent of problems, dampness.
Recent statistics compiled by Archicentre revealed
that 30 to 45 per cent of older homes in inner suburban areas
had a problem with rising damp, also known as salt damp.
Many of these homes may be cured of their problem
by simple remedial or maintenance work. Others will require thousands
of dollars to be outlaid on expensive damp cures.
The Types of Dampness
There are five
types of dampness generally found in homes:
- Rising damp or "salt damp" in brick
walls and masonry.
- Poor drainage.
- Falling damp.
- Horizontal penetrating dampness.
- Condensation dampness.
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Discussions with several damp proofing
companies will soon reveal that there are almost as many
miracle cures as there are different companies. As with
other trades in the home maintenance field there are many
"sharks" around who will happily take your money
but may not cure the damp. More commonly, many of these
companies will undertake expensive and unnecessary cures
when simple cheap cures may have been effective.
Archicentre has seen several instances where expensive
cures have been proposed, when in actual fact no problem
existed in the first place. In one case, a metal shed located
hard against the outside of the wall had caused a large
damp patch on the inside of a wall of an old house. Roof
water drained down between the shed and the wall and an
accumulation of debris meant that the wall was continually
wet. Being an old wall with no cavity, the inside face quickly
became very damp and began to deteriorate rapidly.
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CROSS-SECTION OF THE WALL SHOWING:
1. Falling damp - through
the overflowing gutter
2. Horizontal penetration
3. Rising damp
This wall is built on a strip footing, buried under the
soil. |
The problem could have been cured by simply removing
the shed, allowing the wall to dry out and then treating the outside
surface with a coat of silicone to fill any capillaries.
However, three separate damp companies diagnosed
the problem as being very serious, requiring major and expensive
structural work that varied from replacing the damp proof course
to silicone injection treatment!
Common Causes of Dampness and How to
Eliminate Them
It is recommended that you examine the
following elementary causes before embarking on costly remedies.
a) Inadequate sub-floor ventilation
By far the most common cause of rising dampness
and condensation dampness is inadequate natural sub-floor ventilation.
Lack of ventilation causes a build-up of humidity and minimal
evaporation from the soil and base walls. Both conditions lead
to rising damp and rotting of floor timbers.
Almost all older brick homes have grossly inadequate
provision for sub-floor ventilation and the majority of minor
rising damp problems can be cured by increasing the ventilation
by passive or active methods.
Ensure that existing sub-floor vents are cleared
of any obstructions that reduce their effectiveness. Often concrete
paths or patio floors have been laid in a way that will block
most of the vents, thus rendering them useless. By simply replacing
older vents with new pressed metal vents the airflow may be increased
by a factor of 12. Alternatively, doubling the number of vents
could easily increase the airflow by a factor of 20 to 30. To
ensure that the entire area is ventilated and there are no dead
pockets, it may be necessary to form openings in the bases of
cross walls.
Utilising the drawing capacity of disused chimneys
can further increase natural ventilation quite dramatically. All
that is required is to block off the fireplace and cut holes through
the hearth to the sub-floor. The natural draw of the chimney will
do the rest. Your architect can give you on-site advice on these
remedial measures.
b) Sub-floor obstructions
Sub-floor debris reduces sub-floor ventilation
and should be removed. Sub-floor debris could also contribute
to rising damp if it bridges the damp proof course.
c) Poor drainage
Built-up garden beds, sloping ground or falling
damp could direct water under the house. Drain this away via agricultural
drains sloping away from the house, bedded in loose aggregate.
d) Falling damp
Examine water and stormwater pipes, roofs, gutters
and downpipes for breakages and leaking. Excessive dampness which
is limited to localized patches in soils and on walls indicates
this type of fault. Minor problems can be patched with bituminous
tape or similar. If problems persist, refer to Archicentre's Technical
Sheet on "Roofing and Guttering" and contact a licensed
plumber for major repairs.
e) Horizontal dampness
Elementary horizontal dampness occurs when badly
porous brick walls receive direct rain. The wall can be sealed
by the application of a waterproof coating. Painting on silicone
admixtures is simplest but will require re-painting every few
years, while bituminous paint or similar lasts longer.
Elementary horizontal damp is also caused by
earth bridging damp-proof courses, or obstructions accumulating
water on exterior walls. Once recognised, these problems are easily
remedied by removing the bridge. It is best not to repaint the
walls for some time to allow them to dry out.
Horizontal dampness becomes more important to
remedy when it appears on the inside of the house.
This phenomenon occurs in single brick houses
or in double brick houses where mortar bridging the cavity has
transferred the dampness from the outer wall (see illustration
at top of page).
f) Condensation dampness
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Condensation in the home results from damp
air produced from any of the above causes, or through still
outside air or extreme temperature fluctuations inside the
house. In most cases, condensation will lead to mould growth
and unhealthy living conditions. Implement the remedies
previously described wherever applicable.
Water vapour-producing fixtures like clothes-dryers, stoves
and showers need to be ventilated, preferably fan-forced
to the exterior of the house.
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AN EXAMPLE OF RISING DAMP - Note the
blistering paintwork |
In addition, open windows a little at night and
cut back trees and shrubbery which give the house too much protection
from air and sun. This may also improve sub-floor ventilation
and reduce rising damp. Install insulation to reduce temperature
fluctuations.
Overcoming Damp-related Footing Failures and Damp Floors
In some cases, soil around the house
can become so soggy that it fails to support the house, causing
footing failure and cracking walls. In such cases it is very important
to quickly implement the drainage and falling damp remedies previously
described. In many cases dropped footings need to be underpinned
(refer to Archicentre's Technical Sheet on "Cracking Brickwork").
Damp carpet problems sometimes occur in houses
with concrete slabs. Unfortunately this means the waterproof plastic
under the slab has holes in it and the ground water has seep through
the slab into the carpet.
First try the elementary methods of reducing
soil moisture, but if unsuccessful you'll need to remove the carpet
and waterproof the slab with a surface treatment. Your architect
can help you with this remedy, or refer you to a waterproofing
company. There are many techniques suggested, few are totally
successful and the competence of waterproofing companies varies.
Rising Damp or Salt Damp
The nature of rising or salt damp
Brick and masonry
absorb water, so must be sealed off from contact with moisture
and moisture-bearing substances like soil. If not, water will
rise in the walls causing dampness. When the dampness evaporates
it creates cold clammy conditions in solid brick houses and leaves
behind the corrosive salts which were dissolved in the water.
How to recognise dampness
Look for blistered paintwork, peeling or stained
wallpaper stains and a salt deposit (efflorescence) on walls.
By feeling the walls, you might detect a clamminess
or coldness.
Check for decay in skirting boards, door frames,
architraves and other timber work. Look for mould spots on walls,
curtains, etc.
If a house has been freshly painted or plastered,
it may have been recently done to cover up a dampness problem.
Examine the walls using the above techniques to help discover
any problem.
Causes of Serious Rising or Salt Damp
First, give any elementary cures some
time to take effect. If the problem persists, more costly steps
need to be taken.
Breakdown of damp-proof course
Looking outside the house, you will soon be
able to detect whether or not your house has a damp proof course.
It is usually in the form of a black strip close to the ground
all around your house. Older buildings may not have a damp proof
course at all, as it was common practice by builders late last
century and early this century to omit it as a cost saving device.
Damp proof courses formed using slate, lead or tar may have broken
down in the course of time, or even be damaged during construction.
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Later constructions
Constructions
like concrete paths built directly against the wall and
above the damp proof course, will also encourage moisture
to permeate through to the inside of a building. This problem
will be worse if the new path or driveway slopes toward
the house, accumulating water, or directing it under the
house through the vents. To fix these problems you will
need to either totally remove the concrete, install drainage
grills to clear the water, or lay more concrete taking care
to slope the surface away from the house.
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CROSS SECTION OF WALL SHOWING
bridging of damp proof course
due to construction of a concrete path, causing dampness.
This wall is built on a concrete slab |
Curing Serious Damp Problems
If the damp problem is persistent or
quite severe, it will be necessary to go a step further and engage
a damp proofing company. But shop around, get several quotes,
check the credibility of the company and make sure they give you
a written guarantee.
It is important to obtain independent advice,
so if you have not had a professional inspection of the problem,
a call to Archicentre would be a good investment. Our architects
have saved many people thousands of dollars because of their independent
advice.
There are five major types of cures for rising
dampness used by damp companies but each company may have its
own version of one or more of these cures.
Replastering and installing veneers
The most common method is to scabble affected
damp plaster back to the brickwork and replaster the affected
area with a waterproof plaster or cement mix. This may stop minor
damp problems reappearing but severe cases tend to reappear some
time later above or beside the treated area.
Some contractors replace the entire surface with
waterproof plasterboard. Others use a technique of attaching battens
to affected walls and nailing on plasterboard, providing a 5mm
to 10mm gap between the old surface and providing ventilation
slots top and bottom. All timbers should be decay-resistant and
fastenings rust resistant.
All of these methods fall into the category of
cover-ups rather than cures and consequently cannot really be
considered permanent solutions.
Knapen Tubes
Sloping holes are drilled in the affected area
at skirting board level. Porcelain or similar tubes are inserted
into the holes and the theory is that moisture in the wall drains
into the tubes and evaporates (a sort of mini agricultural drain).
However, the efficiency of this method varies dramatically depending
on external factors such as heating in the room, sun penetration,
humidity etc. Some tests have shown that better results were obtained
when the holes had no tubes in them.
In some circumstances where excessive humidity
and condensation may occur, such as in a bathroom, laundry or
kitchen, the system may work in reverse, making the problem worse.
This system is rarely seen now and is generally
considered to be ineffective.
Installation of a Physical Damp Course
This method has traditionally been regarded
as the most effective (also the most costly) cure for rising damp.
It involves removing a line of bricks close to floor level. Then
a plastic sheet is inserted along the line and the old mortar
is replaced with waterproof mortar. Alternatively, a line is cut
into the bricks themselves with the same waterproofing methods
as above applied. In all cases, only short sections of the wall
can be treated at a time and the joints must be thoroughly filled
and wedged otherwise settlement of the wall may occur.
Each re-mortared section needs to set for around
48 hours before it can take the weight of the wall again.
Alternatively a "self-supporting" damp
course system is available, eliminating the delay needed for setting.
With this system the bricks above and below the cut are no longer
mortared together, but this has not appeared to cause a structural
problem and would be unlikely to do so where only sections of
the house are treated.
Installation of a Chemical Damp Course
Chemical injection under pressure
Chemical injection
under pressure has been used with varying degrees of success in
the U.K. for over 40 years and in Australia for over 15 years.
Pressure injection of a higher alkyl siloxane
solution is the most widely used method in Australia.
Holes are drilled into the bricks at regular
intervals. The solution is pumped into the holes and permeates
the bricks and surrounding mortar creating a broad band of water
repellent brick work. Pressure injection into the mortar course
only is less likely to be successful as old lime mortar is very
weak and often contains many fissures that will cause the product
to blow out before the new damp course is formed.
Chemical impregnation under gravity
Holes are drilled into mortar lines at regular
intervals. Delivery tubes of specific design are placed in the
holes and liquid is transfused into the wall under the influence
of gravity. If sufficient liquid is transfused into the wall it
will form a horizontal water repellent layer in the bricks and
mortar. The solution of choice is a higher alkyl siloxane in hydrocarbon
solvent.
Summary: These methods are very dependent
upon site quality control and use of the correct materials. Many
companies have failed through lack of care, but by selecting a
reputable company, an effective treatment can be completed at
a much lower cost than installation of a physical damp course.
Overcoming Damage Caused by Salt Damp
Especially in South Australia, salts
deposited by water rising up a wall can cause severe structural
damage to the wall. Salt damage can continue to occur even after
replacement of the damp proof course (or other treatment), because
of the action of salts deposited before treatment.
Often this problem, if relatively minor, is simply
covered-over with waterproof plaster or other waterproof coating.
For a noticeably damaged wall, or if you want to adopt a more
thorough approach, you could either:
- saturate and dry the walls to remove existing
salts, or
- wet the walls and apply a poultice of clay
to draw the salts away from the wall (repeating as often as necessary).
It may be awkward to use these treatments while
you are living in the home. An alternative is to apply a "sacrificial
render coat" over the whole surface of the wall. The render
applied is a weak mortar (of 1:2:9 cement / lime / sand for example)
which is sufficiently porous to allow the walls to breathe and
to allow the salt-laden moisture to be drawn into it from the
brick wall, like a semi-permanent poultice.
Over time the render coat will break down as
it "sacrifices" itself while ridding the wall beneath
it of salts. The more lime in the render mix and the less cement,
the quicker the render coat will break down, but the more readily
it will absorb salt-laden moisture over its lifetime. Also when
the time comes to remove it completely, the render coating with
least cement will be easier to remove
Act with all the facts on hand
Dampness problems are usually the outcome
of a combination of causes and only a thorough inspection of the
home will result in a correct diagnosis of the trouble.
A number of methods
of overcoming dampness problems, including general maintenance
items, have been discussed here. Problems which are persistent
may require the help of a damp company, but a careful analysis
of the problems must be made to ensure that the treatment method
prescribed is the correct one.
Remember that the best way of avoiding expensive
problems is to be aware of them before you purchase your house.
The Archicentre Architects Inspection Service has carried out
thousands of home inspections for home owners and prospective
buyers, to help them make a realistic appraisal of the property
before buying, renovating or repairing.
BOOK
AN ARCHICENTRE INSPECTION
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