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BUILDING PATHOLOGY & INSPECTION
Unit 6
Dampness Problems
Dampness Problems
6.1 Learning Outcomes
Understand what is meant by dampness
Know the effects of dampness on buildings and people.
Prescribe the measures that should be taken to rectify a
dampness problem.
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6.2 Sources of Dampness
6.2.1 External sources
Ground water- water that is naturally stored below ground level
and during periods of heavy rainfall the water level can rise and
can penetrate the under building. Moisture can rise through
capillary action and affect the materials within the building.
Flooding- during the period of heavy rainfall and due to poor
drainage, flooding can occur and can seriously damage building
structure and furnishings.
Precipitation/snow- naturally occurring rain and snow provide the
principal moisture sources which affect building elements.
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6.2.1 Internal Sources
Condensation- water vapour generated
by breathing, cooking & washing where it
condense on cold surface throughout the
building thus wetting the building fabric.
Construction moisture-moisture arising
from the construction process. The water
absorbed by the building fabric may take
months to dry out.
Leaking services- defective water supply
pipes, drainage conductors and water
filled heating systems can leak moisture
into the building fabric.
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6.2.1 Internal Sources
Hygroscopic salts- these are naturally occurring salts within the
building materials. They naturally absorb moisture from the air,
resulting in localized damp patches, giving the impression of
moisture within the fabric. Normally a surface effect ie. It does
not penetrate the thickness of the building element.
Human activities- cooking, washing, breathing,
exercising all produce moisture.
Figure 6.1 provides an indication of the
relative amounts.
Paraffin/liquefied gas heater- both liquid &
gas contain a high proportion of water which
enters the building when it is burnt off.
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Hygroscopic salts
The Salt Problem
When dampness has been rising in a wall
for some time, the soluble salts contained
in the ground become concentrated where
the water evaporates, i.e. within the plaster
and
within the wall itself near the apex of rise.
These deposits of salts can absorb water
directly from the air to such an extent that
the wall can become visibly wet. This
dampness effect is entirely separate from
that caused by capillary rise of water and is
usually referred to as “hygroscopic”
dampness.
An example of the pattern (or distribution)
of salt accumulation is shown in Figure (1).
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6.2 Effect of dampness on people
Physical: dampness or increased moisture within the buildings can have
adverse effects on the occupant or users. A damp atmosphere
encourages insects and moulds which can cause allergic reaction. It
also result in the following:
Increases health risks.
Encourages mould growth.
Encourages dust mites.
Triggers asthma/rhinitis.
Social: dampness in buildings can create a perception of poverty, poor
condition leading to the following:
Devalues property.
Reduces comfort levels.
Increases occupants’ distress/depression.
Encourages insomnia.
Dampness Problems
6.3 Effects of moisture on materials
Increased moisture contents will affect to some extent, aspects of the
performance of all building materials. The level at which the material
is affected and also the level at which damage may occur varies with
different materials. Figure 6.1 shows the extent of various moisture
action points on various common building materials.
Damage unlikely- no adverse effect even on a extended period of
wetting.
Action required- where the level of moisture exposure require some
remedial action to be taken. E.g. remove the source of moisture,
introduce drying or ventilation or protect the materials affected.
Damaged likely- where permanent damage or deterioration will occur.
In normal situation reduction in moisture content by drying or
evaporation will cause no permanent damage to overall performance.
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MOISTURE CONTENT DETERMINATION
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6.3 Effects of moisture on materials
Typical effects of moisture on the key building materials are as follows:
Building
materials
Effect of low moisture
contents
Effect of high moisture
contents
Timber
Localised staining which may
disappear as timber dries out;
mould
spores
leading
to
permanent staining; distortion of
thin ply materials.
Permanent staining; irreversible
distortion and bowing of large
section structural timbers; over
time the deterioration of timber by
mould, fungi and insects.
Clay brick
and concrete
block
Localised staining; efflorescence
from salts drying on surface;
increased thermal conductivity;
poor surface absorption (inability
to apply liquid coatings and
sealants); minor surface spalling
during sub-zero temperatures.
Widespread staining and mould
growth; severe surface salt and
efflorescence contamination;
catastrophic failure of component
during sustained sub-zero
temperatures.
Cementitious
and gypsum
based
finishes
Localised surface staining and
salt contamination; lack of
drying following application may
lead to poor strength.
Permanent and widespread surface
staining,
mould
and
fungi;
disrupted finish due to water
expansion (gypsum) and frost
Heriot Watt University
action; catastrophic failure or
collapse.
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6.3 Effects of moisture on materials
Building
materials
Effect of low moisture contents
Effect of high moisture
contents
Mineral wool
insulation
Increased thermal conductivity; mould Ineffective thermal insulant
growth; localized collapse of matrix.
; can act as a ‘sponge’
wetting adjoining materials
(plasterboard);
overall
collapse of matrix.
Plastics
insulation
Little or no effect; some surface No effect to cellular plastics
ponding on horizontal boards.
(extruded
polystyrene,
polyurethane); increased
thermal conductivity due to
absorbed water (expanded
polystyrene).
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6.4 Rising dampness
Masonry walls built from brick, block-work or porous stone and
sitting on wet or saturated soil and built without a physical barrier
to the upward movement of moisture, can suffer from rising
damp.
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MOISTURE LEVELS - Vertically
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Problems
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6.4 Rising dampness
Under pressure from
ground water (water
table) and from a drying
influence
from
the
warmer internal wall
surfaces, water rises by
capillary action vertically
up the masonry wall
above the level of the
ground water.
Capillary Action
Capillary action is the
ability of a liquid to
flow in narrow spaces
without the assistance
of, and in opposition
to, external forces
like gravity. It occurs
because
of
intermolecular forces
between the liquid and
surrounding
solid
surfaces. It is due to
the
pressure
of
cohesion
and
adhesion which cause
the liquid to work
against gravity.
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6.4 Rising dampness
Moisture can rise to 1m high and the extent to which the moisture
extends depends on a number of factors which includes:
Rate of evaporation from the wall,
Pore sizes of the masonry,
Salts content both of the materials and from the soil.
Groundwater level and degree of saturation, and
The use of heating within the property.
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6.4.1 Diagnosing rising dampness
Rising damp is visible by a ‘tide mark’ stain, directly above
ground floor level, on the internal finishes or surfaces of external
walls.
In diagnosing rising damp, observational checks and
measurements can be conducted as follows:
Existence or integrity of DPC- introduce after 1900. Form of
installation and workmanship will determine the effectiveness
and ineffectiveness of the dpc materials.
Bridging of DPC- can be internally(ie. floor screed) or
externally(ie. banked earth)
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6.5.1 Diagnosing rising dampness
Moisture content profile- measuring the moisture content of the
wall at vertically up the wall and horizontally through the wall by
using the ‘Speedy’ moisture meter. Where the moisture content
are higher at low level and are relatively consistent through the
depth of wall, the likely cause is rising damp.
Hygroscopic salts- salts such as nitrates and chlorides can occur
on the wall surface as a result of contaminated moisture
evaporating. Hygroscopic absorbs moisture from the air and
result in staining may give the impression of rising damp. By
comparing the hygroscopic and equilibrium (from drilling)
moisture contents it can be ascertained whether the dampness
is rising moisture or staining from hygroscopic salts.
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6.4.2 Combating rising dampness
To reduce moisture pressure at the base of the wall including the
following:
Remove any bridging earth or ground works.
Introduce a gravel filled field drain at the base of the wall.
Remove any bridging render below DPC level.
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6.4.2 Combating rising dampness
The remedial techniques include the following:
Retrofitted or inserted DPC’s- a slot is formed incrementally along
the existing masonry either by removing bricks or more commonly,
by use of a tungsten carbide tipped saw where a new impervious
DPC material is bedded and grouted into the position with a high
strength, polymer modified mortar.
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6.4.2 Combating rising dampness
The remedial techniques include the following:
Electro-osmosis- relies on either a passive or active copper cable
running round the building perimeter which transfers moisture to
ground by reducing the surface tension.
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Electronic active electro-osmotic
device that emits small tenth of a
second pulses from electrodes inserted
in the wall to the ground.
In this way the polarity between the soil
and the wall is inverted, causing the
ionized water to descend through the
wall to the ground.
The device works without interruption
until the wall is completely dry, when it
switches to an automatic controlled
state.
The system is applicable to any wall
composition and thickness, in which a
hole is drilled every 2 m on one side.
Immediately after installing the device
the walls can be rendered with
microporous
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6.4.2 Combating rising dampness
The remedial techniques include the following:
Siphons- porous ceramic tubes are inserted into slightly inclined,
pre-drilled holes in the damp affected wall. The techniques relies on
moisture being drawn towards the siphons where it can be freely
drain and evaporate to the external air. Salts deposited during this
evaporation can impair the performance of the siphons.
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Gravity Transfusion
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6.4.2 Combating rising dampness
The remedial techniques include the following:
Chemical injection- impervious fluids e.g. silicones, silicates or
stearates are injected into the affected wall either under pressure or
by gravity feed. The technique relies on dispersion of the fluid
through the wall which must be injected at close centres, typically
100-150 mm , to ensure an effective barrier.
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6.5 Condensation
Condensation occurs when warm moist air cools, e.g. when it
comes into contact with a cold surface or plane.
Condensation can also occurs on cold surfaces or, where there
is a positive vapour pressure across a wall and warm moist air
permeates through the building fabric.
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6.5 Condensation
Effects- higher moisture contents can lead to mould and fungi on
surfaces and reduce thermal performance due to moisture
absorption.
Lightweight structures such as timber and steel structure tend to
warm and cool rapidly making them easier to condensation.
Massive masonry construction tends to store heat and cool
slowly, reducing its ability to condense.
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6.5.1 Remedial actions for condensation
Remedial actions include the followings:
Fungicidal washes- clean mould and fungal growths, a short
term solution unless condensation is resolved.
Ventilation- increasing the rate of extraction of moist air or by
increasing the amount of fresh (sometimes warmed) air will
reduce the overall humidity and the risk of condensation.
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6.5.1 Remedial actions for
condensation
Remedial actions are as follows:
Thermal insulation- introducing
thermal insulation into the
building fabric will reduce the
heat losses thereby increasing
the internal temperature and
reducing
the
risk
of
condensation.
Either
by
internal cavity or external.
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6.5.1 Remedial actions for condensation
Remedial actions are as follows:
Vapour control layers- the use of impermeable or high vapour
resistance membranes or materials, on the warm side of the
construction, can reduce the risk of warm moist air permeating the
structure and condensing on colder elements. The effectiveness of
these layers relies on lapped and sealed joints and no penetrations.
Thermal Bridging
Thermal
bridges
are
junctions
where
insulation
is
not
continuous and causes
heat loss.
A thermal bridge occurs
when there is a gap
between materials and
structural surfaces. The
main thermal bridges in a
building are found at the
junctions of facings and
floors, facings and cross
walls; facings and roofs,
facings and low floors.
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6.6 Penetrating dampness
Penetrating moisture typically arises during periods of high
winds and heavy rain, i.e. external water under pressure. Water
can be driven through porous materials, e.g. bricks, stone,
mortar joints, cemetitious renders, causing localised damp
patches internally.
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6.6 Penetrating dampness
When assessing penetrating moisture the following aspects of the
building should be considered:
Location and exposure- buildings constructed on hill tops, near the
source of water(i.e. coast, river) are typically more exposed to
wind driven and at higher risk from penetrating moisture.
Orientation of building facing direct to prevailing wind are at a
higher risk.
Construction- buildings build from modular bricks , block and
stones with mortar joints and sealants are at a higher risk than
buildings constructed from large or continuous panels. Solid stone
or blocks built without cavity are at higher risks. Openings reduces
a walls ability to restrict the passage of wind driven rain.
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6.6 Penetrating dampness
Condition- poorly maintained finishes, renders and seals markedly
increase the risk of water penetration.
DPC’s, flashings- poorly installed or missing DPC’s and flashings
around openings or abutments can reduce the resistance of the
wall at these locations leading to water penetration and staining
internally close to these details.
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6.6.1 Correcting penetrating dampness
Remedial works to rectify defective mortar joints, poorly installed
DPC’s or dirty cavities can be drastic and troublesome. As mother nature
persist, planting of bushes and trees may provide some form of protection.
Corrective measures can include the followings:
Repointing - this involves raking out the existing mortar joints and re-filling
with a weather struck finish. This reduces the risk of water penetration at
deteriorating or recessed mortar joints.
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6.6.1 Correcting penetrating dampness
Corrective measures can include the followings:
Water repellents- application of a liquid waterproofing solution which is
absorbed into the surface of porous building materials which reduces the
absorption of water into the walling material and also the rate of
evaporation from the wall. water repellent treatments are short lived, 4 to
7 years.
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6.6.1 Correcting penetrating dampness
Corrective measures can include the followings:
Flexible sealants- used at joints and intersections between
components to reduce the risk of water penetrations. Care need to be
taken to ensure compatibility with adjoining materials and effective
backing support to sealant.
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6.6.1 Correcting penetrating dampness
Corrective measures can include the followings:
Renders- cement or polymer modified cement based renders can
provide some protection from penetrating moisture.
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6.6.1 Correcting penetrating
dampness
Corrective measures can include
the followings:
Rain-screen cladding- design in the
form of slates or tiles hung on
battens;
uPVC
or
timber
siding/weather boarding or profiled
metal sheeting, it provide physical
barrier to wind and rain, which
reduces the water pressure and the
risk of water penetration. Thermal
insulation can be incorporated into
the cladding to reduce condensation
which might require planning
authorities approval prior to
installation for aesthetics concerns.
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6.7 Conclusions
Moisture affect buildings by staining, mould growth, impaired
performance and potentially affect the health of the building user.
To identified the source of moisture and apply effective remedial
measures.
To adopt systematically assessing methods to identify the source and
interpreting the collected data, the surveyor can provide a remedial
solution.
If the source is man made, than correction will be by convincing the
guilty parties to modify their behavour.