German DIN standards of humidity measurement
Internationally, this system is considered as the most scientific and precise, and has legal force in litigation. The German DIN standard proposes a system to perform this measurement in a direct way to know the amount of humidity inside the walls. This method consists of making a hole in the wall to at least half of its thickness with a power drill, at low speed with a 20mm drill, taking into account to collect all the material that is extracted from the wall. This material is then weighed with a precision scale of divisions of 1mg. The extracted material is dried before weighing again. The drying procedure uses a carbide pump, that although they are a little expensive, their results are unquestionable, and legally accepted. Another drying procedure is with a microwave at 600ºC for 6 minutes, and repeat the process to check that the weight of the dry material has not changed.
The weight difference is the water that existed in the sample, and allows for calculation of the amount of water per kg of existing construction material. If you want to know the percentage in volume we have 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
Suppose that the material extracted from the wet wall is 50g
After drying the material weighs 42g.
The proportion of water will be 50-42 / 50 = 0.16 or 16% water by weight.
The wall is considered dry when the proportion in weight of the water in the interior is less than 6%.
If we multiply by the density of the construction materials that we consider 2.5kg / l we obtain 0.40 which represents 40% of water in volume in the wall.
Disadvantages of the DIN humidity measurement system
- The measure is an average of what was found when drilling, and it does not detect if there are pockets of humidity inside the wall as we do not know what moisture exists around the point of drilling.
- If it is drilled too quickly, the extracted material is heated, and evaporates part of the water found affecting the accuracy 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 limits us to make an extensive study of the distribution of humidity in a building, because it will require many holes at different heights.
- To study the evolution of humidity in a building it would be convenient to do 3 measurements over time, starting one at the beginning, another at the end of 6 months, and another 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.
With electro-physical systems, its control is necessary to evaluate the evolution of the humidity in the walls, and verify the positive effects of equipment. Although the installers started using the DIN method, its inconvenience were so significant that alternative measurement options have been sought.
Electrical resistance humidity measurement
A method used for each measurement point, consists of nailing two pieces of duralumin into the wall, a couple of centimeters apart and that penetrate the wall about 4cm. The resistance between the two points is measured and thus there is an indication of humidity up to 4 cm inside the wall.
One obvious drawback is the presence of these inserts in the wall, spread over the whole house, and that they have to remain installed until the control is finished which can take up to more than a year.
The variation of the humidity in the walls is reflected in the readings, although the humidity is only measured up to 4cm deep.
For superficial surface moisture, electrical resistance meters are used that have two very sharp steel tips that push against the surface of the wall, penetrating a couple of mm into it.
The advantage of this method is that it does not leave signs on the wall, and multiple readings can be taken on the walls without time and aesthetic problems.
All equipment that measures electrical resistance to deduce moisture have the problem of the salts, which appear on the surface of the walls when the water dries by evaporation, since they are conductive and also absorb ambient humidity, giving readings as if there were more moisture than what actually exists in the wall.
Before making moisture readings at a point on the wall, it is essential to remove the salts from the surface by rubbing with a cloth or brush.
Measure humidity by capacitance methods
Another method to measure the humidity in the walls is based on measuring the dielectric losses that exist in the walls.
The sensor is basically a metal ball that rests on the wall and measures humidity up to 4cm deep.
It has the advantage that it does not leave damage on the wall and allows multiple readings in a short time, and without the need of specialized technicians.
Obviously, in thick walls we do not know the situation inside, but knowing the superficial values are inferred for the interior. Again, you have to remove the salts rubbing in the area where measurements are to be taken.
Image of humidity with Thermographic Cameras
Thermographic cameras offer the best solution for measuring the humidity in the walls, since they record the temperature emitted by the walls with great precision, and consequently, where water accumulates and in what quantity.
There are currently thermographic cameras that can be coupled to a Smart-Phone and that cost around € 300. This process allows us to have a thermal radiography of the walls, which greatly facilitates tracking the evolution of drying, storing the data that it can be downloaded in a computer for further processing.
Another application is to locate the humidity on the walls, and see their source of entry into the buildings.