FAQ about building moisture

When a wall is damp, the moisture inside it naturally evaporates toward the surface. This vapor works its way beneath the wallpaper, dampens the glue and creates pressure that makes the covering swell and peel away.

Two causes may lie behind this moisture in the wall: rising damp by capillary action (groundwater rising through the wall from its base) or water damage (burst pipe, infiltration). Identifying the right cause is essential because the treatment differs in each case.

When a wall is damp, the water vapor evaporating toward the surface puts pressure on coatings from within. This pressure eventually lifts and bursts the paint layer.

Two causes can produce this moisture in the wall: rising damp by capillary action or water damage. Painting over it without treating the cause only postpones the problem: the moisture will continue to evaporate and will damage the paint again.

Moisture inside a wall, whether caused by rising damp or water damage, migrates toward the surface to evaporate. In the case of rising damp, this evaporation concentrates at the bottom of walls, where the moisture arrives from the ground and where it exits.

The vapor puts pressure on the render from inside the wall, causing it to swell and gradually crumble. Renovating the render without treating the cause only postpones the problem: as long as moisture continues rising in the wall, it will keep damaging the surface.

No. HYGRO acts on the wall's physical behaviour, and its relevance depends on a precise on-site analysis of the building: the materials, the height of the rising damp and the site's configuration. Without that prior diagnosis, no result can responsibly be promised.

That is why MURSAIN installs HYGRO itself, after confirming that the situation really concerns rising damp that needs treatment. The equipment is passive and autonomous, with no wearing parts: once installed, the house is equipped for the rest of its life.

A dehumidifier and a dryer both treat moisture contained in the air of a room: they capture and remove it, improving comfort and limiting condensation. They are especially suitable after water damage, to dry saturated structures.

But when the moisture comes from capillary rise, meaning water rising from the ground into the walls through porous materials, they can only act on what ends up in the air, not on the source inside the wall. HYGRO acts on the very mechanism that makes water rise in the wall by neutralising the energy potential that allows that rise.

Both devices extract moisture from the air in a room, but their technology and operating range differ.

A dehumidifier works by condensation: it cools the air until the water vapor liquefies and can be collected. It generally becomes efficient from around 15 C and gains efficiency as temperatures rise.

A dryer, or adsorption dehumidifier, uses a hygroscopic material that fixes water vapor on its surface. It can work at lower temperatures, but starts to lose efficiency above about 35 to 40 C.

The choice between the two therefore mainly depends on the temperature of the room to be treated.

In a wall affected by rising damp, water migrates from the ground upward through the wall by capillary action. This movement relies on a natural energy potential: the damp base of the wall is positively charged while the drier upper part is negatively charged. It is this difference in potential that draws water upward.

HYGRO acts at the source by neutralising this energy potential, which stops moisture from rising in the wall. It applies principles of applied physics, including work attributed to Mr de Laplace, was developed by Mr LECARPENTIER and has been in use for more than 40 years.

Passive and autonomous, with no wearing parts, it is installed by MURSAIN after analysis of the causes. Once in place, the house is equipped for the rest of its life.

MURSAIN offers a 3-year performance guarantee on HYGRO installation. This means that if the process does not produce the expected effects on rising damp within that period, MURSAIN refunds the equipment and removes it.

This guarantee reflects confidence in the process: results must be measurable and observable over time, not only at the moment of installation.

As soon as you notice signs of moisture in a building: saltpeter (white or powdery deposits at the base of walls), a damp band, flaking paint, peeling wallpaper, crumbling plaster, or persistent mould.

It is also advisable before buying an older building, especially one built before 1960, even if no visible signs are present, because rising damp may already exist without yet showing on the surface.

The remote diagnosis, based on your observations and photos, provides an initial analysis of the causes. An on-site assessment is then carried out if necessary.

Adsorption is a physical phenomenon in which certain molecules, such as gases or vapours, attach themselves to the surface of a solid without penetrating it. Unlike absorption, where the substance enters and integrates into the material, the molecules remain on the surface.

This is the principle used in dryers: a hygroscopic material captures water vapor from the air by fixing it on its surface, then can release it under heat to regenerate itself.

Absorption means that a substance, liquid or gas, penetrates into a material and dissolves or integrates within it. A classic example is a sponge absorbing water, or a porous wall absorbing ground moisture by capillary action.

Adsorption means that molecules of a gas or liquid attach themselves to the surface of a material without entering it. This is the operating principle of dryers, which use the surface of a hygroscopic material to capture water vapor contained in the air.