Damp investigations

Additional equipment for stage 4 Carbide meter including calcium carbide powder and safety goggles. Gravimetric sampling. Mechanical floor hygrometer or humidity box CCTV to view drains, or other tests. Fluorescein dye tests. Thermal imaging camera. Hydrogen gas pressure testing equipment and gas detector. Air bags and pumps for drain leakage. Salts analysis kits for detection of: sulphates, chloride and nitrate salts. PH kits for water testing. Sterile sampling self-sealing bags and cotton buds for mould swab samples for later specialist analysis. Sterile plastic containers to take water sample for specialist analysis. Also useful: logging devices for checking condensation patterns, surface temperatures, dew point over time (environmental conditions); u value calculations to determine heat loss –thermal resistivity of external walls; devices for checking floor screed moisture levels; light and power will be needed on site (unless cordless drills and portable lighting available); and small fold-up table or bench to work on.

Stage 4 may apply to a whole building or to the further investigation of a damp zone identified from a stage 2 or stage 3 investigation.

A stage 4 investigation is usually undertaken in the context of a specialist dampness investigation, so more time is spent by the surveyor to focus on dampness issues. The thinking process will be targeted very closely to dampness diagnosis, rather than taking up a proportion of the time for a general building survey.

Techniques at stage 4 include destructive tests and possibly examinations requiring 'opening up'. The emphasis in this fourth stage is very much on 'sampling'. The aim is to confirm moisture conditions within structural elements (primarily walls, but also floors) by drilling out masonry samples. Drilling and sampling techniques are described fully in Surveying equipment and tests and in the case studies.

The additional time for wall drilling and sampling, and the carbide tests, for a 3-bedroomed house, could be up to 1 hour for each wall position tested, assuming that 3 holes are drilled, with brick, mortar and plaster samples taken. Salts tests of samples in position will add a further 30 minutes. Time can be saved if just brick dust is sampled. However, time spent on stage 4 tests could save many days of unnecessary work on costly and potentially damaging remedies.

The decision on where to sample depends on the kind of investigation undertaken and prevailing site conditions. A typical investigation could involve first sampling at various positions laterally to confirm a damp zone, followed sometimes by vertical sampling where damp patches extend upwards markedly. It could also include a close examination of a solid floor, where a hammer and bolster could be employed to chop out an area of screed; skirtings could be levered off to reveal perhaps perimeter floor membrane detailing; or floor hygrometers could be employed to assess moisture conditions of the floor. On occasions you may need to drill a hole carefully in a solid floor so that a humidity sensor can be sealed into the hole to determine equilibrium relative humidity.

A typical stage 4 investigation of an average-sized house with very average moisture conditions, where the objective is to seek out and diagnose dampness, could involve drilling 10 to 12 holes. If, on the other hand, the aim was to collect sufficient evidence of moisture conditions in a building to prove or disprove a diagnosis of dampness in connection with a legal dispute it has been known for walls to be virtually machine gunned full of more than 75 holes. The aim of such blanket drilling could either be to obtain so many samples that there is not an iota of a doubt in the diagnosis they underpin, or conversely that there would be within the large collection of data obtained a few results that would back up nicely the preferred diagnosis.

Monitoring

Monitoring involves making observations of building condition or performance over time. House surveyors are familiar with monitoring in the context of building movement investigations, which typically require building cracks to be carefully measured for their width and direction at intervals over at least 18 months. Such monitoring enables us to assess whether the building is subject to seasonal movement, whether movement is progressive, and the direction of movement. The table below is an example of the monitoring table you should draw up for each station under scrutiny.

Date of visit	Resistance/capacitance meter readings	Deep probe readings	Carbide meter readings	ERH of drilled hole	Visual changes	Comments

In the context of a dampness investigation, monitoring might be necessary to:

• identify or eliminate seasonal effects (internal and external);
• assess the effects of a remedy that has been applied;
• assess building performance in a range of weather conditions;
• assess building performance in relation to lifestyle; and
• assist in the elimination of causes and sources of moisture.

Monitoring moisture conditions can be as simple as visual inspections over time. However, staged mapping of relative readings (of masonry or plaster) or timber moisture content readings give a more accurate means of observing surface moisture conditions over time, providing that readings are not influenced by salts or metals.

More sophisticated monitoring techniques may also be employed (usually associated with a stage 3 or stage 4 investigation). For example, repeated testing over time of moisture content by carbide meter could be useful. However, one of the difficulties is that drilling 1 hole in a brick actually changes conditions for the brick. It now has a hole, and this could help the material to dry out.

Equilibrium relative humidity (ERH) observation may be more useful. One advantage of this method is that at least you are not returning at intervals to remove more and more material from the wall at a given point of study. It is easy to take readings in sleeved holes in masonry, where ERH should stabilise after 30 minutes.

There is not yet enough feedback from practitioners on the usefulness or reliability of such monitoring, although there has been an increase in the use of sensors to monitor wall temperature and relative humidity for flooded properties.

Other monitoring methods include:

• data logging – environmental measurement (for condensation investigations);
• logging and retesting of salt deposition/formation;
• mould species analysis; and
• water sampling analysis.

The case studies give further examples of monitoring in action.

Data loggers

Data loggers are computer-programmable devices, often used by specialist investigators, but their use is likely to become more widespread. They are typically used to monitor the drying out of buildings or to log air temperature, relative humidity and vapour pressure. The data is stored and then downloaded onto computer and presented by graph for analysis.

Figure 1: Humiloggers similar to this were used in case study 9 Gone with the wind. These instruments record air temperature, relative humidity and surface temperature. They have the option to connect additional hygrometers and thermisters as well as a wood moisture equivalent probe, useful in taking additional moisture readings of timber and external air temperatures. The purpose of these instruments is to record and store data over set periods. These instruments may also be connected with additional telemetry for remote monitoring from site. They are invaluable for monitoring both internal microclimates and the drying out of a building, e.g. after flooding

Diagnostic chart for key stages of dampness investigation

Source	Stage 1: visual inspection	Stage 2: investigation using moisture meters	Stage 3: detailed investigation
Air moisture condensation	Mould likely, often 'crescent' shaped at room corners, behind cupboards and in unheated rooms. Water droplets on impervious surfaces.	EMM reading high but often below 100 at surface plasters and timber. Tailing off gently at edge of damp area.	Hygroscopic salts present could indicate a secondary moisture source. Meter in 'condensator' mode can confirm live condensation or how far surface temperature is from dew point. Deep probe testing can help confirm that significant dampness is at the surface only and therefore more likely to be condensation.
Penetrating dampness	Stains, mainly on ceilings and walls. May be mould present. Check external condition of roof and walls. Note condition of roofs, walls, rainwater goods, etc. Note damp stains, dark patches, green staining externally.	EMM readings may focus to source.	Nitrate and chloride result typically negative, but sulphate results can be positive due to building materials present. Deep insulated probes from the EMM may help ascertain whether an element, e.g. masonry wall, is significantly damp within its thickness, i.e. readings above 17 R/R.
Internal plumbing leaks	Localised stains and damage. Leaks often cause rot outbreak where pipes run in ducts. Dampness can cause surface mould. Look for characteristic fanning stains to plasters.	Moisture meter readings can help you trace the epicentre of dampness and link it to a source, e.g. pipe leak.	Any water sourced from the water main contains nitrate, chloride and sulphate ions, and salt deposition at surfaces can arise from evaporation. Salt present can be confirmed by site tests.
Below-ground moisture	Skirtings and joinery damp, and stains/damaged/blistered plasters adjacent. Damp floor patches. Damp zone identified. Wall dpc may be noted.	EMM readings high at base of walls and floor tail off sharply. Often to 100 due to salt. Not usually higher than 500mm. Taking EMM readings along walls just above skirtings can flag up a damp zone and then be linked to visual observation internally and externally.	High nitrate concentration likely, but nitrates can originate from a number of sources.
Underground drain leaks	Localised internal damp patches may be evident if leaks from blocked or leaking gullies externally are just below the ground and near to the building.	High moisture meter readings local to a leak may be the first symptom of a problem.	Negative chloride and nitrate results from a water sample could help eliminate waste potable water and foul drains as a source of the moisture problem. However, the same results may not eliminate a potential leak from a rainwater drain from the dampness investigation.
Flooding - natural or due to internal pipe bursts, etc.	Damp stains on top floor ceilings are often the clue to a loft pipe burst. Flooding often self-evident – the result of dramatic events. Floods over solid floors often problematic.	A moisture meter will not be needed when flood damage is self-evident. Moisture meters can give an indication of whether building fabric is drying out after a flood, but mainly at the surfaces.	Useful role here for electronic humidity sensors, which can be convenient for monitoring building fabric as it dries out, when they can be inserted into drilled holes – particularly suitable for walls.

Diagnostic table continued

Source	Stage 4: homing in (carbide meter especially)	Further tests and notes
Air moisture condensation	Carbide test can confirm positively whether a building element is significantly damp within its thickness: if dry – condensation is a likely cause if wet – there may be another source, e.g. penetrating dampness.	Remote monitoring can help link condensation to changes in building conditions or lifestyle effects over time – remote monitoring (using data loggers) is becoming more user friendly as computer software and instruments improve and develop.
Penetrating dampness	Carbide test for MC at depth can confirm whether the element is wet at depth, and prompt further tests to be carried out, e.g. to monitor drying out after remedy applied. A wet inner wall could mean condensation (and mould) is a result of damp penetration rather than a cause of a damp problem.	Internal symptoms may be linked to rainfall pattern –a diary is useful. Pencil mark the fringe of a stain to see if it is increasing in size. Common at the base of walls where rainsplash and pooling of surface water give false impressions of 'rising damp' affecting internal walls.
Internal plumbing leaks	Carbide tests can confirm significant dampness, help pinpoint moisture concentration and help monitor the drying out after repairs.	A range of tests can be used to confirm or trace a plumbing leak but some tests require pipework to be drained down. Assistance from a plumber or a services engineer may be required. Listening sticks are useful for identifying and sometimes locating pipe leaks.
Below-ground moisture	Carbide tests may confirm wall is significantly damp through its thickness. MC readings reduce with height. Confirmation of significant dampness in a building element's thickness does not automatically link to a particular moisture origin. Invasive tests could confirm a damaged or poorly detailed floor dpm. Mechanical hygrometer used to confirm floor moisture content.	In view of the extent of remedial work sometimes needed to control or stop damp rising from below ground, all other potential moisture sources must be eliminated to confirm the rising damp diagnosis. This may mean staged remedies and monitoring. DPCs used from 1877, but often effectiveness is compromised by poor detailing or building changes.
Underground drain leaks	Surveyors can test drains from shallow chambers, using air, water or smoke. For testing deeper chambers employ a drainage specialist. Pour water into gullies to test for blockage and watertightness.	CCTV surveys may be useful, but do not always include anything more than a cursory visual inspection of gullies and inspection chambers. These could require further tests, e.g. water or air test. Film footage may be open to interpretation. Drains usually need water jetting to allow access of CCTV camera.
Flooding – natural or due to internal pipe bursts, etc.	Carbide meters may be used to test drilled samples – and to help monitor moisture content after a flood.	Flooding may be 'natural' or caused by services leakage. Flood reports available from Environment Agency. Beware property on a 'flood plain'.