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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. Dampness Problems Dampness Problems 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. Dampness Problems 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. Dampness Problems 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. Dampness Problems 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). 7 Dampness Problems 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. Dampness Problems MOISTURE CONTENT DETERMINATION Dampness Problems 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. Dampness Problems 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). Dampness Problems 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. Dampness Problems Dampness Problems MOISTURE LEVELS - Vertically Dampness Problems Dampness Problems 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. 18 Dampness Problems 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. Dampness Problems 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) Dampness Problems 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. Dampness Problems Dampness Problems 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. Dampness Problems 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. Dampness Problems Dampness Problems 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. Dampness Problems 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 Dampness Problems 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. Dampness Problems Gravity Transfusion Dampness Problems 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. Dampness Problems Dampness Problems Dampness Problems 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. Dampness Problems 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. Dampness Problems 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. Dampness Problems 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. Dampness Problems 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. 38 Dampness Problems 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. Dampness Problems 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. Dampness Problems 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. Dampness Problems 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. Dampness Problems 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. Dampness Problems 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. Dampness Problems 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. Dampness Problems 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. Dampness Problems 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.