The most common way of diagnosing dampness problems or generally rising damp is by using dampness meters.
Just like cars - not all dampness meters are created equal. There are many brands and types of damp meters and depending on how sophisticated (expensive or cheap) they are, they deliver very different results.
The "quality test" of dampness meters or the most important quality parameter is their penetration depth. The deeper a meter can penetrate the wall fabric and detect moisture, the more advanced technology it uses and the more it cost. The reverse is also true: cheap damp meters can only measure the wall surface, while more advanced / expensive ones can measure further in depth.
Here are the 3 main types of dampness meters in use today.
1. Resistance Meters
Resistance (Pin / Prong) Meter
These are the least expensive and lowest in class. On average they cost about £15-20 and can be purchased pretty much everywhere incl. Amazon and eBay.
They can be recognized from its two sharp pins. These meters measure conductivity; more exactly they measure the resistance of building material between the two pins with a small electrical current - hence their name: resistance meters. Because damp materials conduct electricity better than dry ones, the meter can differentiate between various levels of dampness based conductivity.
These meters have originally been developed for measuring the moisture content of timber but later they have been adopted by the construction sector. Due to its low cost they became very popular with the damp proofing industry and became the de-facto standard. They are also known as Protimeters based on the company who first manufactured them.
Any criticism on dampness meters is pretty much about this meter. The main criticism: they have no depth penetration, they read the surface only. It can give us an indication about the condition of the walls but makes them unfit for any serious or in-depth diagnosis - yet they have been used for decades, and they are still widely used today.
If your building has been surveyed recently or if you received a damp proofing quote good chances are the professional diagnosis you have received has been based on a resistance (pin) meter. Thanks to some leading voices in the UK building industry more and more people now are becoming aware of their limitations and they are slowly being replaced by newer technologies; mainly the capacitance meters, which we are going to discuss next.
2. Capacitance Meters
Capacitance meters are a newer technology and they slowly started replacing the old resistance meters. They only have one round electrode, as a result they won't leave holes in the walls or plasterboard.
The electrode of the meter sends a small current through the wall towards the ground and based on the conductivity of the material will estimate its moisture content.
Unlike resistance meters that only read the surface, capacitance meters penetrate up to about 40-50 mm depth, so they give a better diagnosis about the walls.
3. Microwave Meters (Radar principle)
Microwave meters are the newest technology. They have only been developed a few years ago so they are still considered emerging technology. They work on the principle of ground-penetrating radar: the shoot a weak microwave beam into the wall fabric and read its reflection. Damp areas reflect the microwaves differently from dry areas and based on these differences the meter gives appropriate reading.
Microwave damp meters are least known (practically unknown) in the UK although they are becoming part of the standards in more and more European countries. They offer some major benefits in comparison to other meter types, as they:
- Provide the most accurate measurements
- Have the deepest penetration, some can detect moisture up to 800 mm deep
- Are impervious to ground salts, they only read on moisture
The downside: their high cost. One of these meters, depending on their accessories, can cost well over £1,000 so only professionals can justify the cost. They are bundled with various software solutions that allow further in-depth analysis of the walls, e.g. the creation of a moisture distribution chart that can visually display the moisture content of the walls.
Here are some samples images on the type of analysis these microwave moisture meters permit.
It is important to understand that damp meters are not absolute tools that give a foolproof diagnosis. Although modern damp meters can be a great tool that allows us to "see" beyond the surface, they should be used in conjunctions with other observations and measurements.
The practical experience of the surveyor is also important; an experienced one can much quicker can correlate the various data obtained from various sources, to come up with a rock solid diagnosis.
There are a whole suite of other moisture diagnosis tools that can provide additional insight into the status of the walls - we briefly cover these next.