Moisture meters are commonly utilized to determine the moisture level in building materials, and there exist two common types of moisture meter: conductive and capacitance meters.
Conductive meters establish an electrical circuit through the meter by positioning two probes on the surface or embedding them in the wall. The meter calculates the electrical resistance, which is influenced by the moisture content present in the wall.
Capacitance meters, on the other hand, place either the meter itself (carrying conductive plates) or a separate head (carrying conducting concentric rings) on the surface of the wall to measure moisture content. The meter readings determine the fringe capacitance in the sensor, which is influenced by the level of moisture in the brick. These meters usually measure the moisture content at a depth of 20mm but this depends on the density of the material being investigated.
It is also important to note that moisture meters have the potential to provide significantly misleading results, whether intentionally or due to lack of experience. Although moisture meters can measure the level of moisture in the material, they may yield an artificially high reading in the presence of hygroscopic salts. Hygroscopic salts absorb moisture from the air and this poses a problem, as damp and salt often occur together due to the hygroscopic properties of many salts. Hygroscopic salts can be found in brick and plaster samples, where the building materials have come into contact with soot from chimney breasts, animal dung in the past or from leaking water and drainage pipes and other various sources.
Furthermore, it is crucial to use moisture meters on appropriate materials. Most moisture meters are calibrated for use on softwood as other building materials such as brick, plaster and stone are much more variable. Therefore, when employed on materials like brick, plaster, stone, or mortar, they only provide a qualitative reading. The meter can be used to determine whether a wall has consistent levels of dampness or if dampness is higher at the wall’s base and lower at the top (a potential indication of rising moisture).
It is also important to note that wood is never completely dry due to its tendency to absorb moisture from the surrounding air. As such, a reading of 10-12 percent on a moisture meter is typically not a cause for concern. On the other hand, if the moisture levels exceed 20 percent, the wood may become more susceptible to rot, fungal and insect attack. If a moisture meter indicates saturation, it is likely due to a source of moisture other than humidity, such as a leak.
Instead of using moisture meters, the carbide method can be employed to assess the level of dampness, although it is more invasive since it necessitates taking samples of the material being investigated. The samples are combined with calcium carbide powder in a pressure vessel that is equipped with a gauge. The calcium carbide reacts with any water in the sample, producing acetylene. The amount of acetylene generated corresponds to the moisture content present in the wall.
The carbide method can be done on location and takes roughly 15 minutes per sample. However, it cannot differentiate between ground moisture and hygroscopic moisture, although comparing samples taken from the surface and deeper within the wall can provide a reasonable indication.
However, to get a true indication of the moisture content of the material being tested we recommend the samples of the masonry are tested in a laboratory using the gravimetric method. Similar to the carbide method, this process involves drilling out one or more samples of the material to determine its moisture content. Although it is more time-consuming than using a moisture meter the results are much more precise. It is important to note as the samples are taken off-site for testing, they must be placed in an airtight container to prevent any changes in moisture levels during transit.
At Heritage Damp Surveys, we have our own in-house laboratory so we can calculate moisture content (MC) and hygroscopic moisture content (HMC) of a material, while also identifying common salts. Using multiple samples allows us to create a dampness profile, which can aid in identifying the type of damp and determining the appropriate remediation measures.
The use of thermal imaging plays a vital role in validating our observations and also aiding in diagnosis. For instance, if we notice a patch of mould on the inside of the wall, we will use thermal imaging to determine the underlying cause. Is it due to a cold area prone to condensation exacerbated by damp penetration from a leaking rainwater downpipe or failed chimney stack flashing? The thermal image will reveal a cold trail down the wall, confirming the presence of a leak. Conversely, if no cold trail is evident, the issue may have been resolved, and the mould may residual from a previous leak. Thermal imaging is also useful in identifying areas of missing insulation, detecting where cold air infiltrates a building during winter, and locating wet cavity wall insulation. In particular, we find thermal imaging especially effective in identifying random cold patches in a wall where cavity insulation is soaking wet and cooling the wall down. Thermal imaging cannot confirm the cause of a damp problem on its own but back to our original point, it can confirm in aiding diagnosis.
Salt Test Kits
A salts test kit is used to determine the presence of moisture and damp in a given area. This test is performed to identify the type of water affecting the area by detecting chlorides (which are present in tap water) and nitrates (found in ground water, indicating potential rising damp on walls).
These two tests can be useful in detecting water leaks as they enable the user to test an area that is affected by moisture and identify the specific source of the water. This helps to confirm the existence of a leak or rule out other types of damp such as penetrating damp.
It’s worth noting that, while a salts test is a helpful tool in leak detection, it should be used in conjunction with other information to identify and locate the cause of moisture and damp problems. It cannot find a leak or source of the moisture problem alone, but it can assist in understanding the source of the moisture.
The primary purpose of a salts test is to check for nitrates and chlorides. Nitrates are found in water that has come into contact with the ground, soil containing manure or fertiliser or even leaking drains containing urea. Soot deposits from a chimney breast will also contain nitrates and these salts can affect adjacent walls surfaces next to the chimney breast, particularly when there is a source of moisture such as condensation or a leaking flashing. Chlorides, on the other hand, are usually found in treated tap water. Tap water is treated with chemicals such as chlorine and fluoride to clean and filter it, making it safe to drink and disinfecting it to prevent the spread of waterborne diseases. However, please note that the presence of chlorides does not necessarily mean that the moisture comes directly from a pipe leak as it could also be due to waste water from toilets or washing machines.
A thermo-hygrometer is used to determine the relative humidity, which is the amount of moisture in the air compared to the amount of moisture the air can hold at that temperature. So in an environment at 100% relative humidity any moisture produced by cooking and showers etc. will immediately condense on any surfaces such as walls, windows and ceilings. This is very useful when diagnosing damp problems particularly with respect of condensation and mould. The thermo-hygrometer that we use also calculates the dewpoint of a surface so we can determine whether the surface is at risk of condensation forming. The information taken on site can then be used to diagnose the cause of the condensation problem and remedial works.