How symptoms may be misinterpreted

A damp wall does not necessarily mean "rising damp"! Visible moisture contamination may be caused by one or a number of contributing factors which, to the inexperienced investigator, could be misinterpreted. Rising damp, lateral or penetrating damp and condensation are all problems of concern but result from different causes. Skilful, intelligent analysis could save thousands of dollars as incorrect or deceitful diagnostic practices could lead to considerable unnecessary expenditure. Many symptoms are common to different causes.

As certain types of dampness inside a home are not related to rising damp, you can undertake a preliminary review to help ascertain whether your home is actually suffering solely from "rising damp", an alternative source, or a combination of sources.

True "rising damp" is normally associated with surface salt deposits, crumbling fretting bricks, mortar loss, bubbling flaking paint with visible surface salts, and deteriorating plaster and should not be confused with saturation from other sources or the masonry’s own natural "ambient" moisture content. Diagnostic tools will not only indicate moisture but through the skilful interpretation of moisture concentrations and positions, the source and direction of moisture ingress can be deduced. A "damp" reading alone will not confirm rising damp unless other factors, including the location and direction of moisture ingress, are considered. At 4% moisture content some mortars may be considered dry whilst others at the same 4% moisture content could be considered damp, similar variances apply to clay and concrete bricks as well as natural stones. Where surface salt deposits are not visible the experienced investigator should perform a salt detection test to confirm the presence of dissolved hygroscopic ground salts. Pinpointing the source of moisture is extremely important as causes may range from leaks around windows, leaking bathroom/kitchen plumbing, leaking down-pipes and/or spouting, condensation, inadequate sub-floor ventilation, incorrectly designed ducted heating systems etc. Electronic diagnostic tools, such as the TRAMEX Moisture Encounter, (used on calibrated setting No. 3), or the Protimeter Surveymaster SM or MMS, (in sonic "Search Mode"), are quick and easy to use devices that will give an immediate indication of the presence of moisture up to depths of 15mm.

As the density and porosity of masonry materials will vary considerably the same amount of moisture content will have a different % moisture contents in different materials. Electronic moisture meters are excellent “tracking” devices where, expertly used, the variance in readings, i.e. higher or lower, will pinpoint the direction of moisture travel and assist in pinpointing the source location. These instruments do not measure % moisture content but read electrical or "sonic" signals that will use the moisture content or other conductive materials as a conductor interpreting "signal-out" versus "signal-in" as an indicator. Many two-pronged “probe” type moisture meters, such as the Protimeter Mini C, are calibrated solely for use in timber, (when used for survey work on masonry they must be used with Insulated Deep Wall Probes). Testing should also be conducted to confirm the presence or absence of dissolved hygroscopic ground salts as well as checking temperature/dew-point characteristics where contamination could be from condensation or other sources. An electronic moisture meter placed on a mirror will give a “high” reading due to the “silver” conductor on the rear, similarly placing the meter on your arm or forehead will also give “high” readings – neither the mirror nor, (hopefully), your forehead suffers from “rising damp”! Rising Damp Common Symptoms - Stained walls, blistering, salt-ridden and flaky paint, curled, stained and delaminating wallpaper, white salt powdered residue, fretting, powdering and eroded brick and stonework, powdery disintegrating mortar, rotting timber skirting-boards and door-frames. Rising damp is normally associated with surface salt deposits, crumbling fretting bricks, disintegrating mortar, bubbling flaking paint with visible surface salts, and deteriorating plaster.

The source of true rising damp is capillary ground moisture climbing up through the internal pores of the masonry carrying damaging ground salts in solution. Moisture finds its own level and once the masonry has become saturated the moisture level rises with the lower masonry always being the wettest. Only when the masonry has been fully saturated does the moisture rise and at this point the masonry will be equally wet on both sides of a solid wall or both leaves of cavity brickwork sharing a common damp-course. As the moisture evaporates from the surface a “hairy looking” crystalline surface salt deposit appears on the exposed surface. “Rising damp” requires support from sufficient soil moisture content and natural active water table content. Active “rising damp” will not occur during extended periods of severe drought and in many cases months of above average rainfall is required to bring up the water tables and soil moisture contents to induce and support rising damp.

“Rising Damp” has no associated musty smell and is a natural deterrent against mould growth. Consider the medicinal properties and use of saline solutions for treating open wounds or as a mouthwash. The salt laden Dead Sea is not a highly recommended fishing ground. Our own Australian farms suffer poor harvests and grazing through salinity. “Rising Damp” is the only type of damp contamination that introduces hygroscopic ground salts. High salt content and visible presence, brick, stone plaster and mortar disintegration are true indicators of “salt” contamination and if not visibly present the experienced investigator should perform a salt detection test.

Poor sub-floor ventilation.

Common Symptoms - Musty damp smell, stained walls, blistering and flaky paint, curled, stained and delaminating wallpaper, rotting timber skirtings and doorframes, swollen warped, (cupped),floorboards, rust stains around nail-heads.

Where symptoms of dampness appear on the wall surfaces above a suspended timber floor, (i.e. blistering paint, delaminating wallpaper), at skirting board level and only slightly higher, with no surface salt deposits, an initial appraisal would indicate poor sub-floor ventilation. As moisture evaporates from the sub-floor soil it will penetrate and saturate the floor timbers and in an attempt to escape, will permeate up behind skirting boards to evaporate from the plastered/masonry surface. Higher concentrations are quite common at internal corner intersections where internal sub-floor masonry walls have no cross-ventilation openings and moist air is trapped in stagnant air pockets. Damp, musty smells and/or buckling and warping floor timbers are all good indicators. The floor-boards/sheeting should be checked with a suitable electronic moisture meter for moisture content. A salt detection test performed on the walls surface which indicates the absence of dissolved hygroscopic ground salts will rule out “Rising Damp”. Powered sub-floor ventilation systems will assist in reducing moisture-laden air from under suspended timber flooring but will not halt capillary moisture rising deep inside the masonry.

Lateral or penetrating damp.

Common Symptoms - Stained walls, blistering, salt-ridden and flaky paint, curled, stained and delaminating wallpaper, white salt powdered residue, fretting, powdering and eroded brick and stonework, powdery disintegrating mortar, rotting timber skirting-boards and doorframes.

Problems normally occur where external ground levels are higher than existing damp-courses and internal floor levels, and where damp internal concrete floors are not isolated from existing masonry walls. A common occurrence with split-level homes on sloping building sites with internal supporting walls having "fill" higher on one side of the wall than the other. Basements commonly exhibit moisture contamination permeating through the walls from the external higher soil levels. Surface salt deposits would also be apparent. Footpaths may also be constructed against an outside wall higher than the damp-course creating a "bridging" effect. "Bridging" of cavities by mortar droppings and other debris is often another contributing factor.

Leaking down-pipes or gutters, internal plumbing, shower bases, garden sprinklers, etc, are also possible sources of penetrating damp but being saturated with clean “tap” water would not contribute to salt content.

Condensation

Common Symptoms – Mould, stained walls and delaminating wallpaper, rotting timber skirting-boards and doorframes.

Condensation problems occur when warm moist air comes in contact with cooler surfaces and black mould appears. Condensation symptoms may well be visibly evident long after the event has occurred. Winter condensation damage may well leave long lasting visible evidence. All buildings have a degree of moisture always present in the air, breath, perspiration, warm washing water, clothes driers, showering, boiling water for tea or coffee, to name but a few sources of warm water vapour. Perimeter walls, windows and ceilings provide a temperature or heat barrier, normally warmer on one side than the other. At the interface between warm moist air and cooler walls and windows, the water vapour will be cooled becoming liquid again, creating fine droplets. Readily seen on glass surfaces, more porous materials, such as wood and plaster, will provide some measure of absorption - a haven for airborne mould spores - thus encouraging mould growth. “Damp” readings found higher up on wall surfaces, in corners, near or on the ceiling, behind paintings, wall hangings, bed-heads and wall furniture, partially drawn drapes and poorly heated and ventilated perimeter rooms, would indicate condensation. The dissolved salt content in true “rising damp” discourages mould growth. Mould spores being sensitive to salt contaminated materials. Electronic instruments are available that will measure and compare air temperature and wall temperature and calculate a “Dew Point” to confirm the possibility or presence of condensation. These tests are only relevant when certain comparative temperature differences are present.

Poorly ventilated external masonry wall cavities can also suffer from condensation occurring within the cavity and without adequate air flow the condensed water vapour can saturate masonry quite quickly. This can often be determined by using an electronic moisture meter on the external wall surface. Higher readings may be revealed below brick window sills and mid-way between external brick vents. In many instances the masonry will be visibly wetter, (darker in colour), above the damp-course level.

Electronic moisture meter readings do not diagnose “rising damp” but are often presented as “evidence” that “rising damp” exists by inexperienced or deceitful assessors.

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