What is a Magnetic DPC?
A magnetic damp proof course (or magnetic DPC) is the latest technology that can permanently solve rising damp based on the latest research on the mechanism of rising damp and breathability.
A magnetic DPC can prevent the rise of moisture in any building fabric without invasive physical interventions, by reducing the surface energy of the wall capillaries - this resulting in decreased capillary adhesion and increased breathability.
Here is a detailed video explanation of the magnetic DPC technology, explaining how it can dry out old walls affected by rising damp non-invasively. Plain English explanations with lots of simple research data about rising damp, breathability (vapour permeability) and how to deal with rising damp in a building-friendly way.
The concept of magnetic DPCs has been around in various forms for over 30 years. It has been developed by Electronic Engineers familiar with many aspects of building physics, applying their knowledge of Electronics onto damp buildings.
The original concept of the technology came from the medical MRI technology (Magnetic Resonance Imaging), a tissue-friendly body imaging technology which uses magnetic fields that interact with the water molecules of the body, replacing the more damaging X-ray radiation. Based on that a solution it has been envisioned that weak magnetic fields could be used to reduce the bonding of water vapors to capillary surfaces.
Over the years various patents have been filed for both passive and active (non-powered and powered) systems. We have listed a few of these patents here from the Google Patents database.
Click on a title to expand its content.
This German patent from 2018 describes an electronic device that can influence capillary flow behaviour in masonry with magnetic pulses, by influencing the electrical potential of the electrical double layer.
According to the inventor, an electrical potential build-up occurs inside the capillaries on a continuous basis. The generated magnetic pulse train interferes with this, resulting in a reduction of capillary forces: "the magnetic pulse sequences influence and modify the surface tension of liquid in the capillaries in such a way that the weight of the liquid gains the upper hand and the liquid in the capillaries sinks and can flow down out of the capillaries".
This French patent from 2009 describes a passive (no power required) resonator type device, comprised of a set of electrical circuits, each of them made of a number of circular conductive concentric rings with opposite openings for the reception of telluric waves.
According to Lenz's law - an induced current in a circuit opposes the cause that generates it - these rings create a local electromagnetic field opposite (180° out-of-phase) to the disturbed terrestrial electromagnetic field, cancelling its action over the entire area of action of the device, which is about 10-30 m depending on the number and configuration of conductive rings used.
According to the author, old damp walls become dry within 6-18 months, after which the walls are protected from any capillary rise during the entire operating life of the device.
This French patent from 2008 is composed of 3 independent inductance-capacitance oscillator circuits for neutralizing electromagnetic wavelengths of telluric (Earth) origin in the VHF, UHF and microwave bands (30 MHz - 3 GHz). This invention is an improved version of a patent from 1988 from the same author, providing wider bandwidth and simpler construction.
This German patent from 2005 describes a powered device consisting of a flat Tesla coil placed in the vicinity of a damp wall (without touching it).
The application of a high-frequency weak pulsed electrical field breaks the attraction between the capillaries and water molecules, resulting in the water falling back into the ground under the effect of gravity.
This German patent from 1989 describes a non-invasive powered wall dehydration system composed of a pulse generator  and a passive LC oscillating circuit (resonator)  which is connected to an antenna, that emits low-powered electromagnetic pulses to break the capillary bond between the wall fabric and water molecules. According to the author, the range of the device is about 20 meters.
This French invention from 1988 describes two parallel oscillating circuits made of 4 spiral inductors, 4 capacitors and 4 rigid dipole antennas, mounted on insulating supports - the whole device being housed in a protective box permeable to electromagnetic fields. The unit also features an energy discharge circuit that can periodically discharge the accumulated energy of the oscillating circuits to the ground.
The device collects electromagnetic energy from the environment. its oscillating circuits create a reverse-phased field to the incoming field, which results in the cancellation of the osmotic pumping effect inside the wall capillaries. In addition, when the incoming electromagnetic fields are intense, some of the energy is discharged to an earth connection.
This US invention from 1980 presents two passive (unpowered) resonant circuits, each of them comprised of a spirally wound flat coil (inductance) connected to a capacitor located in the center of each coil. The two flat coils [1, 11] are mounted perpendicularly to each other, housed in a plastic boxlike container.
The energy of the apparatus is supplied from outside by the abnormally high electrical and magnetic fields (interference of stray fields) always present in areas of rising damp. This energy drives the two oscillatory resonant circuits, which according to Lenz's law - an induced current in a circuit opposes the cause that generates it - creates a local electromagnetic field opposite (180° out-of-phase) to to the incoming field that creates the capillary rise, reducing its effects - resulting in the dehydration of the building over the entire area of action of the device.
Although the idea that electromagnetic fields can interact with water and its bonding to solid surfaces has been observed for quite some time, the underlying mechanisms have not been understood.
It took science several decades to "catch-up" and answer some of these missing questions. Recent technical discoveries on the mechanism of rising damp, the factors that affect breathability and vapour movement resulted in a much comprehensive understanding of the topic of moisture movement, also clarifying the main mechanisms on how the magnetic DPC system works and affects the wall fabric.
Working Principe – Simple, Non-Technical Explanation
The working principle of the magnetic DPC can be summarized in a nutshell as follows:
Old buildings contain moisture in both in vapor and liquid form trapped inside billions of capillaries.
The wall fabric primarily dries out by evaporation. The rate of evaporation or breathability of the wall fabric is determined by two factors:
- Moisture barriers: certain plasters or materials (e.g. cement plaster, plastic membranes, certain paints etc.) applied on the surface block evaporation, resulting in moisture accumulation inside the wall fabric. Removing these materials (physical moisture barriers) restores breathability and makes the wall fabric drier.
- Surface energies: the surface of all solid materials contain small amounts of static electricity - known as surface energy or surface charges or adhesion forces - which are strong enough to attract and bond the tiny water molecules to capillary surfaces, resulting in some moisture accumulation.
Surface energies control the evaporation rate of the wall fabric: high surface energies result in more moisture retention and less evaporation, while low surface energies in easier evaporation.
In case of rising damp, salts (electrically charged salt ions) deposited in the capillaries can significantly increase the surface energy of the wall fabric, resulting in increased moisture bonding and decreased evaporation / breathability, even if the wall fabric is otherwise breathable with no moisture barriers. This explains why the lower part of old walls in the rising damp zone (subject to water and salts) dries much slower than the upper part (subject to water only).
The magnetic DPC reduces the moisture content of the walls by decreasing its surface energy, resulting in better breathability and more evaporation. This technology complements the removal of cement or other moisture barriers, and can improve the breathability of the fabric even when removing moisture barriers would be unpractical, too invasive or too costly.
Working Principle – A More Detailed Explanation
Here is a more detailed explanation on how the magnetic DPC technology works.
Water Vapours vs. Liquid Moisture
Water in masonry is present in two forms:
- As gas (water vapours), and
- As liquid (capillary water).
Because liquid water is visible, damages caused by it become obvious and traceable to cause.
Water vapours, on the other hand, are invisible. They are present everywhere, even in the driest desert. Where there's air, there are water vapours present.
Vapours are also extremely light. To put it into perspective: 1 gram of liquid water contains 3.34 x 1022 (about 1 trillion x 10 billion) water molecules - an incredibly large number in each gram of liquid water. Being so light, vapours can be influenced by incredibly small forces in nature, including the tiny electrical charges of solid surfaces (surface energy), or the electro-chemical charge of certain materials (e.g. electrical charge of salt ions) - these can attract and trap water vapours, causing moisture to accumulate.
Water vapours being so invisible and so light, it is easy to neglect or underestimate their effect in comparison to the more tangible liquid water, and mistakenly assume that liquid water is more important than water vapours. Due to their extreme numbers and their ability to closely interact with other molecular phenomena, water vapours are just as significant as liquid moisture, especially in slow long-term processes.
Earlier DPCs - Target Liquid Moisture
Damp proof course technologies of the past have tried to keep walls dry by blocking the rise of liquid moisture. The focus was on stopping liquid moisture.
Recent research has shown that ongoing vapour intake from the damp ground can also cause rising damp, vapour accumulation being a standalone wetting mechanism. If given enough time, vapour accumulation will result in liquid moisture and capillary action.
Magnetic DPCs - Target Vapours & Breathability
The magnetic DPC technology takes a completely different approach to dampness control. Unlike previous DPC technologies which focus on liquid moisture, the magnetic DPC focuses solely on vapour movement or evaporation, the main mechanism how damp walls dry out. The magnetic DPC does not attempt to block the movement of moisture, but on the contrary: it makes it possible to very easily escape from the wall fabric by reducing the bonding power of water vapours to capillary surfaces. Less bonding = more evaporation = drier wall fabric. The magnetic DPC assists evaporation and makes the wall fabric more breathable.
When researching how water vapours interact with capillary surfaces, an important discovery has been made: a completely breathable wall fabric with no moisture barriers not only retains moisture but that can build up to substantial levels.
This initially seemed like an anomaly, however further research has identified two important factors that determine the breathability of the wall fabric. These are:
- Physical moisture barriers (presence or lack of it)
- The surface energy of the fabric
Surface Energy & Breathability
Physical moisture barriers are externally added materials or coatings which interfere with the free movement of moisture. Most common such materials are cement, plastic membranes and foams. Physical barriers hinder evaporation and thus make a wall fabric less breathable. It is important to understand that breathability is a fine gradient scale with many values rather than a yes-no proposition. The degree of breathability of various materials is measured by the vapour diffusion resistance (μ), the lower this number the more breathable the material.
Surface energy or surface charges can be regarded as a form of "static electricity" that is always present on all solid surfaces. This energy is strong enough to attract and bond the tiny water molecules to the surface, leading to moisture accumulation. High energy surfaces can bond and retain more moisture for longer, also making much more difficult for the moisture to evaporate, even if the wall fabric is breathable.1Yin, X., Gupta, V., Du, H., Wang, X. & Miller, J. D. Surface charge and wetting characteristics of layered silicate minerals. Adv Colloid Interfac 179, 43–50 (2012)
The surface energy of materials can be altered by multiple mechanisms, including:
- Physical means (e.g. by smoothing, polishing, blasting)
- Chemical or Electro-chemical means (e.g. by using solvents, cleaners, surfactants), or
- Electromagnetic means (e.g. by altering the surrounding EM environment)2Wang, Y., Wei, H. & Li, Z. Effect of magnetic field on the physical properties of water. Results Phys 8, 262–267 (2018)
Here are some examples of various effects that can alter the surface energy of the masonry, which came to light during recent research.
A prime example of this would be the electro-chemical effect of ground salts. Charged salt ions can significantly increase the surface energy of capillaries creating high-energy charged surfaces. These can trap much more water, resulting in more wetting and moisture retention (hygroscopic effect), reduced evaporation and decreased breathability of salty walls.
The graph below demonstrates this concept. We have compared the behaviour of two identical bricks - one salty, the other one not - in a humid environment. The moisture retained by a salty brick (green) was about 4 times more (141 g vs. 33 g) than the moisture retained by the non-salty brick (blue). High-energy charged surfaces also let go of the moisture much slower, the salty fabric (green) drying out much slower (here about 7 times slower) than the non-salty brick (blue).
The surrounding electromagnetic (EM) environment is also affecting damp walls in multiple ways.
The EM environment is invisible to the human eye, but it can be visualized with measurement instrumentation. For e.g. magnetic fields can be visualized with magnetometers. Using high-end magnetometers which can detect small rapid changes of the magnetic field, we can observe that the magnetic variations in the room around the walls (orange) are absorbed by the walls, inducing (generating) in the fabric small induced voltages (red) and currents (blue), which mirror the magnetic changes closely.
Although the magnetic variations in the room (orange) are relatively small (about 1-2 nT), they can create a substantial effect on the even tinier water molecules of about 0.1 nm in diameter.
Inspecting the induced currents (blue) in the wall fabric closely, we can see that they have very sharp fronts, being able to charge up the capillary surfaces.
Longer term, the currents in the wall fabric (blue) mirror the magnetic variations in the air (orange) very closely, showing that magnetic fields in the environment indeed affect the wall fabric.
Decreasing the Surface Energy to Improve Breathability
To improve the breathability of a wall fabric, one can do the following:
- Remove the moisture barriers or existing non-breathable materials (e.g. cement plasters, foams, membranes, non-breathable paints etc.) restoring the walls' natural breathable condition. This is usually done by replastering the wall with a breathable lime plaster.
- Decrease the surface energy of the wall fabric so the wall can release some of its bonded moisture that normally won't evaporate. This can be achieved with the magnetic DPC system.
To decrease the surface energy of the masonry, the electromagnetic (EM) approach makes most sense as EM fields can easily penetrate large solid walls and able to affect the wall fabric non-invasively, a fundamental requirement of conservation practices.
The magnetic DPC system is an electromagnetic “drainage” system that absorbs certain EM fields in the building. Once installed, its internal circuitry absorbs some of the surrounding magnetic fields, channeling the collected energy into the ground via an earthing connection.
Same as a pump that drains liquid water out the building, or a dehumidifier that drains the vapour moisture out of the room, the magnetic DPC “drains” the room of some of its EM energy that contributes to the bonding of water vapours to capillary surfaces. Less EM energy in the room leads to less surface charges and less vapour bonding, resulting in a drier masonry.
Decreasing the surface energy of wall surfaces can further increase the breathability of the wall fabric, complementing the removal of moisture barriers. This can make a significant difference in the "rising damp zone", near the lower part of the walls, where natural evaporation can be significantly inhibited by the presence of salts.
In cases when the removal of moisture barriers or existing plasters or renders would be too invasive, unpractical or too costly, the magnetic DPC can still be applied as a non-invasive standalone solution to reduce the moisture content of the wall fabric, most of the time making a significant difference.
Magnetic DPC - Internal Construction
This is achieved with a precision aerial system mounted in a protective case. Inside the case there are a number of circuit boards with several spiral antennas etched onto them.
Antennas (or aerials) are energy converters. They pick up electromagnetic (EM) energy from the environment and convert it to an electrical signal which is usually amplified or processed - just think of a TV or mobile phone.
The spiral antennas of the magnetic DPC system operate on the same principle. They pick up and convert the EM energy into electrical signals, which, instead of being amplified, are sent to the ground and discarded through the unit's earthing connection. As a result there is a constant energy flow from the unit to the ground, the unit constantly "draining" the environment from its EM energy.
The decreased EM energy reduces the surface energy of the walls, resulting in reduced bonding of water molecules to capillary surfaces, more evaporation allowing the wall fabric to reach a newer, drier state of equilibrium. Remember, the unit is affecting the tiny water vapours, which are 3.34 x 1022 (about 1 trillion x 10 billion) lighter than a gram of water, so the vapours can be influenced by extremely small energy changes.
Here are some actual photos of some of our residential units showing the internal circuitry. Large range commercial units are much more complex with additional circuitry, but the overall working principle is the same.
The range of the various units varies between 10-30 metres, depending on the type of the unit, so in the majority of cases one single DPC unit covers the whole footprint of the building. The active range can be affected by the thickness and layout of the walls and the installation location of the unit in the building. Typically, they are installed on the ceiling of the ground floor in a service area (under stairs, hallway, pantry, utility room, cellar etc.) to keep them out of sight, but other installation locations can also be considered.
As the DPC units do not contain moving parts, they have an extremely long lifetime (several decades), the main limiting factor in terms of service life is the longevity of the internal circuitry, which are decades. The systems do not have running costs and do not need maintenance.
Here are a few UK installations showing the fitted DPC systems in different buildings.
Nowadays the ever-increasing amount of electromagnetic (EM) radiation can be a cause of concern for some. This is because most telecommunication devices (such as mobile phones, Wi-Fi routers, smart appliances etc.) perform a dual function: they both receive and transmit EM waves. Because they transmit, they output a small EM radiation which can add up.
Zero EM Output, No Interference
it is important to understand that the magnetic DPC system, by design, only receives energy from the environment and does not transmit (outputs) anything. As such, it won't interfere with any telecommunication equipment from your household or workplace.
Here is the manufacturer's EC Declaration of Conformity, certifying that the system passes all relevant European Electromagnetic Compatibility (EMC) standards.
As mentioned, the magnetic DPC decreases by a small extent the amount of EM radiation present in the environment. Based on actual measurements the magnetic field decrease 5 metres away from the magnetic DPC unit is about 2.5 μT (micro Tesla) or 2,500 nT (nano Tesla), which is a very small amount.
To put this into perspective: here is some third-party figures comparing the intensity of typical magnetic field values from the environment and various applications:
- The magnetic field caused by a (shielded) microwave oven 1 foot away is 4-8 μT
- Earth's magnetic field varies between 30-70 μT, depending on latitude and location
- A pacemaker can be safely exposed to a magnetic field of about 500 μT
- A typical refrigerator magnet creates a 5,000 μT (or 5 mT) magnetic field
As you can see, the changes produced by a magnetic DPC unit are negligible to the human body (1.5 to 2 metre in size), but are significant to the vapour molecules in the walls (0.1 nm in size), these being about 10 billion times smaller than the human body.
Moisture Reduction Effect
The dehydration effect of the magnetic DPC has been subject to extensive testing through embedded sensors by taking consecutive readings from the the depth and surface of masonry as well as the surrounding environment – monitoring the movement of moisture throughout the wall fabric.
Here are some photos of the experimental setup and some of the sensors used during the testing.
Magnetic Field Changes
Shortly after the installation of the magnetic DPC we can notice a significant drop in the surrounding magnetic field. The drop is about 2,500 nT (nano Tesla) or 2.5 μT (micro Tesla) - very significant to the 0.1 nm sized water molecules, but highly insignificant to an infinitely larger human body.
Wall Surface Energies
Changes in the ambient magnetic field (green) results in changes in the wall surface energy (red), resulting in increased moisture evaporation, leading to electrical charge movement and electrical current flow changes (orange) inside the wall fabric.
Changes in Moisture Content
The change in the magnetic field (green) and the increased vapour movement and evaporation leads to a gradual and consistent decrease in the moisture content of the wall fabric (blue) - measured by the embedded microwave sensor. The rate of the moisture change in this experimental setup amounted to about 0.1% by weight every 2 days - the equivalent of about 1.5% moisture decrease per month. This figure doesn't refer to relative humidity (RH) but to real liquid moisture content or absolute humidity change in relation to the weight of the material (% by weight).
To put this into perspective: the porosity of a brick is about 25% - a dry brick containing 75% solid material and 25% air (which can be filled with water). Thus when a brick is saturated with water, it can contain up to about 25% of moisture. On the other hand, dry bricks in real life contain about 2-3% of moisture, depending on their age, porosity and salinity.
The moisture content of damp bricks in real life commonly varies between 4-12%, a saturated state being not that common, and it's usually caused by rainwater ingress rather than just rising damp.
The real moisture content of any masonry can be measured with special moisture analysers via drilled-core (gravimetric) measurements, or with high-end microwave sensors. Drilled core readings are one-off (spot) measurements, while microwave sensors allow the continuous tracking of a wall's moisture content in real-time.
A 1.5% per month moisture drop highlighted above allows an 11% damp wall to dry out and return to a normal dry state in about 6 months, reversing a long-term rising damp problem ongoing for several decades, If the wall fabric's breathability is affected by moisture barriers, the dehydration takes a longer time.
Such a result can not be achieved by the removal of the moisture moisture barriers (e.g. cement) alone, the surface charges of the masonry also must be addressed - improving the breathability of the wall fabric by both mechanisms.
- Moisture can be found in the wall fabric in two forms: as liquid and as vapours.
- While older damp proof course technologies have focused on the liquid moisture, the magnetic DPC focuses on the vapour movement and makes the walls more breathable.
- The breathability of the wall fabric can be improved by either removing the moisture barriers, or by decreasing the walls' surface energy.
- Higher surface energy traps more moisture, resulting in damper walls. Lower surafce energy results in drier walls.