German DIN standards of humidity measurement
Article by Juan Vinyes, PhD in Physics.
The German DIN standard proposes a direct method for performing this measurement to determine the humidity level within the walls. This method involves drilling a hole in the wall to a depth of at least half its thickness using a power drill, operated at a low speed, equipped with a 20mm drill bit. It's important to collect all the material extracted from the wall. Subsequently, this material is weighed using a precision scale with divisions of 1mg. The extracted material is dried before reweighing. The drying process employs a carbide pump, which, although somewhat expensive, provides indisputable results that are legally accepted. Another drying procedure involves using a microwave at 600°C for 6 minutes. Repeat the process to verify that the weight of the dried material remains unchanged
The difference in weight represents the water content in the sample and facilitates the calculation of water quantity per kg of the current construction material. To determine the percentage by volume, one needs to multiply the weight of the water by the density of the construction materials, which is approximately 2.5kg/l.
Let's do a practical example
Let's assume that the material extracted from the damp wall is 50g
After drying, the material weighs 42g.
The water proportion will be calculated as 50-42 / 50 = 0.16 or 16% water by weight.
The wall is deemed dry when the proportion in weight of interior water is less than 6%.
By multiplying with the density of the construction materials we consider as 2.5kg/l, we get 0.40, equivalent to 40% water by volume within the wall..
Drawbacks of the DIN humidity measurement system
- The measurement represents an average of findings during drilling, and does not identify pockets of humidity within the wall since we lack knowledge of the moisture distribution around the drilling point.
- If it is drilling is done too quickly, the extracted material heats up, and evaporates causing a portion of the water to evaporate, thereby affecting the precision of the measurements.
- The aesthetic impact is considerable, and holes can only be pierced in discrete points or behind furniture or household appliances. This inconvenience constrains us from conducting a comprehensive study of humidity distribution in a building, as it would necessitate numerous holes at various heights.
- To study the progression of humidity within a building, conducting three measurements over time would be beneficial—initially, at the outset, then at the conclusion of 6 months, and finally after one year.
- The initial holes must be sealed to prevent water from evaporating and do not influence the successive measurements, which will be made, making holes next to the previous ones.
When using electro-physical systems, When using electro-physical systems, their monitoring is essential to assess the humidity evolution within walls and to confirm the equipment's positive impact. Despite installers initially adopting the DIN method, its significant drawbacks prompted the search for alternative measurement methods..
Electrical resistance humidity measurement
A method utilized for each measurement point involves embedding two pieces of duralumin into the wall, positioned a few centimeters apart and penetrating the wall by about 4cm. The resistance between these two points is measured, providing an indication of humidity within the wall up to a depth of 4 cm.
One apparent drawback is the existence of these inserts in the wall, dispersed throughout the entire house. Furthermore, they must remain installed until the monitoring process concludes, a duration that could extend beyond a year.
Changes in wall humidity are evident in the readings, even though the measurements are confined to a depth of only 4 cm.
In the case of surface-level moisture, electrical resistance meters equipped with two finely pointed steel tips are employed. These tips press against the wall's surface, penetrating a few millimeters into it.
This method's advantage lies in its non-destructive nature, leaving no marks on the wall. It allows for multiple readings on walls without causing temporal or aesthetic concerns.
Every apparatus that employs electrical resistance to infer moisture encounters the issue of salts. These salts become visible on the wall's surface as water evaporates, as they are conductive and absorb environmental moisture. Consequently, the readings can indicate higher moisture levels than what genuinely exist within the wall.
Before conducting moisture measurements at a specific wall point, it's crucial to eliminate surface salts by gently rubbing with a cloth or brush.
Measure humidity using capacitance methods
An alternative method for measuring wall humidity is grounded in assessing the dielectric losses inherent to the walls.
The sensor comprises a fundamental metal sphere positioned against the wall to measure humidity up to a depth of 4cm.
One of its advantages is its non-damaging impact on the wall. It facilitates multiple swift readings and doesn't necessitate specialized technicians.
Undoubtedly, the situation within thick walls remains unknown. However, by grasping the surface values, inferences are made about the interior. Once more, it's crucial to eliminate surface salts by gently rubbing the area where measurements will be conducted.
Visualizing humidity using Thermographic Cameras
Thermographic cameras provide the most effective solution for humidity measurement within walls. They achieve this by meticulously capturing the temperature emissions from the walls, thereby indicating both the location and volume of water accumulation.
Presently, there are thermographic cameras available that can be integrated with a smartphone, with an approximate cost of €300. This setup enables us to acquire thermal radiography of the walls, significantly aiding the monitoring of the drying process. The collected data can be stored and later downloaded to a computer for additional analysis.
Another use is to identify the areas of humidity on the walls and ascertain the sources through which moisture infiltrates the buildings.