Damp walls are a troublesome issue for many people. There is a reasonable way to deal with it.
First I would like to shed light on the causes. Unfortunately, the problem of damp walls is also present in new buildings, but in general we primarily encounter damp walls in old buildings. When I talk about damp walls, I mean walls, where the moisture comes out of the wall and not moisture on the (plastic paint) wall surface (condensate), which in combination with dust leads to mold.
The walls are usually damp from the inside because no horizontal barrier was provided. A horizontal barrier is a water-impermeable layer that is provided horizontally in the masonry above the foundations.
A second horizontal barrier is often installed 60-80cm above the ground so that rain splashes near the ground do not continue to rise up the wall.
In old buildings, the 50-60cm thick walls are usually buried approx. 60-80cm into the natural soil without sealing them. The better stones were turned towards the surface of the wall and the inside of the wall was filled with inferior stones and clay. Due to the mass of absorbent material, the moisture content within the wall is automatically higher because absorbent material continues to seek moisture until it is saturated.
The moisture in the subsoil replenishes the moisture that evaporates higher up over the wall surfaces. The continuous capillary moisture migration from bottom to top dissolves the minerals present in the earth and all building materials, which we call salts, which then crystallize there when the moisture evaporates on the wall surface in an area approx. up to one meter above the ground. Over time, so much salt accumulates in the base of the wall and near the wall surface that this salt binds eventually more moisture from the environment and surrounding air than comes from below. That’s why it’s not helpful at this stage to create a subsequent horizontal barrier, for example by ramming in sheets.
Often you can see that the wall plaster near the floor has already been replaced – in the belief of progress on a sealing cement basis – and as it progresses, new moisture damage can now be seen directly above the “new” plaster. Other concepts seal the wall to its full height, be it with plastic plaster and reinforcment net, tiles or thermal insulation that is glued directly to the wall. The moisture is locked in the wall, and the moisture in the room air can only be removed through ventilation and dehumidifiers.
A different approach seems to me to make more sense for our health and that of the wall and has proven itself. First of all, the existing plaster is removed inside and outside and the wall is given as long as possible time to acclimatise. Then a new wall is built in front of the old one at a distance of at least 5cm. This wall can be made from thin bricks, plasterboard or clay boards.
In our case we used CLAYTEC clay boards with a highly absorbant white clay plaster finish, avoiding wall paint and the associated lower water vapor circulation.
It is important that every connection to the floor and the “problematic wall” is designed in such a way that moisture transport cannot occur at the points of contact.
The 5cm air gap is ventilated through sufficiently large openings in the floor and ceiling area so that no accumulated moisture can remain.
When using clay panels, additional moisture is removed. This dry wall surface can now be plastered with clay plaster. In this way, the wall surface is not only guaranteed to remain dry, but the “more” in clay used helps to regulate the humidity that is still present in the room without having to set up dehumidifiers.
We practiced a similar approach outdoors by modifying the usual base design. We use natural stone slabs that have covered ventilation slots at the top and bottom to ventilate the space between the stone slabs placed at a reasonable distance from the unplastered wall.
This solution consists of three parts: the floor guide with a channel that accommodates the vertical plate. The space between the floor part and the house wall is filled with mortar, tilted slightly forward.
The vertical plate, approximately 80-100cm high, has slots at the bottom and top. The lower slots are high enough above the base to allow air to enter and water to drain out.
The upper slots are covered by the upper bar and are used for ventilation. The upper stone cover is again slotted to accommodate the vertical plate and the pulled-down nose covers the ventilation openings. This upper stone cover is glued to the house wall with its back against a plastering jig, and plastered and fixed from above with the facade plaster starting there.
In order to increase the breathability of the air-lime facade plaster, it was pigmented so that it does not become stuck with coats of paint.
Drainage only makes sense if water is actually directed against the wall in contact with the ground, for example on a slope. The big disadvantage of drainage is the associated sealing of the wall base. The base of the wall is still bare in the earth, and all moisture in the wall is forced to evaporate towards the interior. In addition, drainage systems are usually built without the cleaning openings required on every building corner and in the medium term develop into water collection systems instead of being able to drain the water away because the pipes become clogged with sediment.
Summary: You should not try to “lock away” moisture. The better way is to give the humidity a path without provoking new extremes. Clay is the ideal building material for regulating room air humidity, but must not be applied directly to damp walls.
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