Although damp meters provide a good indication about the condition of the walls, there are cases when additional tests are needed for a more precise diagnosis.
Here are some of the professional measurements we regularly use:
1. Wall Core Analysis (Gravimetric Analysis)
Wall Core Analysis
Wall core analysis, also known as gravimetric analysis (gravi-metric = weight based measurement) is the most accurate filed-based moisture measurement method and it is considered the "golden standard" worldwide.
This is what English Heritage says about gravimetric analysis in their conservation handbook Practical Building Conservation: Mortars, Renders and Plasters, which is used as reference guide by many conservation specialists throughout the country.
“Gravimetric analysis of a drilled sample is the most accurate of the analytical methods, and it is therefore used for calibrating other forms of measurements.”
– English Heritage
The masonry moisture content is determined from drilled powder samples taken from the depth of the wall using a precision scale and drying oven. Each wall sample is first weighted (wet weight), dried, then weighted again (dry weight). During the controlled dehydration the water from the sample evaporates and the sample becomes lighter. The weight loss is the moisture content of the sample explained in percentages.
It's interesting to note that dry walls are not completely dry (0.0%). They still have a small residual moisture content due to the surrounding humid environment. This is called air-dry state, as opposed to the oven-dry state which is an artificial condition that can only be achieved when a building material is dried in an oven for an extensive time.
For e.g. a 4.6% moisture content means that the 4.6% of the sample (e.g. brick) is water.
Gravimetric measurements are mainly used by scientific research facilities due to the cost of the measurement equipment. Each of our engineers have their own portable equipment (gravimetric scale) and can do moisture tests on the spot and tell you the results.
Gravimetric analysis is an improved, more accurate and faster version of the old calcium carbide test.
2. Professional Salts Analysis
Salts Content Analysis
Ground salts are the main cause behind the structural deterioration of masonry. Some salts are found natively in bricks as they are made of clay. However most salts are deposited over time into the building fabric through rising damp or various environmental factors. Salts can either crystallize on the surface (efflorescence) as a white powdery substance or under the surface (subflorescence).
Determining the type and concentration of salts deposited in the wall fabric gives us a better understanding of the aging/wetting process and it is important when determining the renovation process.
We perform a chemical analysis of the three most important salt types:
- Chlorides: are sea salts. The most common sources of chlorides are sea-spray and salts from de-icing roads. They tend to stay soluble over 30% relative humidity. Buildings along the coast or close to the sea are typically affected by chlorides.
- Nitrites: the most common sources of nitrites are commercial fertilizers and manure. Being water soluble they tend to deposit in the upper part of the building; their concentration tends to increase with height and depth. Farm building, barn or stable conversions have typically very high amount of nitrates.
- Sulphates: sulphates are the most dangerous salts for porous materials due to their unique crystallization behaviour. They tend to crystallize on all surfaces regardless of pore size, and due to their longitudinal crystal growth they can exert a high enough pressure to crack the capillaries. Because they are less soluble, they tend to stay in the lower parts of the building.
3. Wall Cavity & Underfloor Inspections
Borescope or pinhole cameras can be very useful as they can provide valuable information from hard to access spaces. This can include the condition of the wall cavity, the composition and structure of the walls (e.g. in case of rubble infilled walls), the underfloor area for inspecting the condition of the floors and joists, or for tracing leaks and building defects.
4. Thermal Imaging (IR Thermography)
Thermal imaging or infrared (IR) cameras have been used by quite some time for masonry diagnosis. Infrared cameras visualize changes in surface temperature and can be used to detect thermal bridges (areas of heat loss), leaks, moisture and water infiltration etc. Damp areas are generally cooler than dry areas and this temperature change can be picked up the thermal imaging camera and provide us additional information.
In addition to the measurements listed here we also perform other tests and measurements to solve specific situations.
Whatever your dampness problem is, we are likely to find its root cause which opens the road to resolution. We also like complex and challenging cases, so far we have solved them all. 🙂
If you have a dampness problem and need some help or guidance in diagnosing it, please get in touch, one of our friendly surveyors will get back to you.
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