"Rising damp" what it is, what causes it, what damage it causes, how to recognize it and how to eliminate or prevent it

MAIN CAUSES OF HUMIDITY

Let's start by saying that rising damp is only one of the many causes of humidity. First of all, therefore, it is necessary to list the types of causes of humidity that can be encountered:

1 - condensation, humidity caused by condensation is the main cause of humidity inside a property. It mainly occurs when the amount of water vapor present in the air reaches the saturation level or the surface temperature of the material is lower than the dew point.

The risk of condensation occurring is aggravated by poor air circulation.

Condensation can occur in two ways:

• superficial, which leads to the formation of mold;
• interstitial, occurs at the interface between two levels. This type of humidity manifests itself with efflorescence, subflorescence and modification of the properties of the materials;

2 - thermal bridges, the thermal bridge is that portion of the casing in which the thermal flow density is greater than the surrounding construction elements.  The causes are usually due to geometric and material inhomogeneity and variation in the thickness of the construction. For more information on the topic, read our article on thermal bridges.

3 - rising damp is easily found in the basement, basement and ground floors where most of the surfaces are in contact with the ground. The humidity will infiltrate the walls and spread in two ways: direct contact and capillary rise.

The physical principle of capillarity allows the water to rise inside the masonry and resurface at any point in the room. Mineral salts are dissolved in the water which react chemically with some components of the masonry and mortar giving rise to inflorescences.

4 - infiltrations, infiltrations can be of two types:

• humidity present in construction materials is mainly due to the presence of water in the preparation phases. This will remain incorporated within the walls during construction;
• humidity coming from the outside, it is an infiltration resulting from atmospheric events. They can be due to accidental, meteoric events or hygroscopic absorption of external humidity;

WHAT IS RISING DAMP, WHAT CAUSES IT AND WHAT DAMAGE IT CAUSES 

This is humidity that rises up the walls because they are not well waterproofed by rainwater, groundwater or present due to accidental causes.

It is therefore caused by the presence of any type of water or humidity and rises through the walls, carrying with it crystals of mineral salts (responsible for aesthetic damage).

Rising damp is mainly caused by poor waterproofing of the foundations. Much depends on the porosity of the masonry and the quantity of water present underground.

The causing phenomenon is given by the dissolution in the water of the salts present in the soil and in the building material, which rise, through the capillary effect, to the surface. Consequently, although the water evaporates, the salts remain in the plaster and once crystallized they increase in volume, pushing towards the plaster and building materials. All this causes unhealthy environments and serious damage related to degradation and static weakening of structures.

Rising damp is the most difficult type of damp to combat, as it usually occurs in the walls facing the foundations, causing an irreversible process of disintegration of the plasters and mortars that bind the masonry.

The degradation left by these sources is generally massive, evenly distributed, with little variation over time. The damage it usually causes is the following:

• compromises the healthiness of the premises;
• disintegration of mortars and plasters;
• weakening of structures (instability of the entire structure in the worst case);
• yellowing of the paint;
• detachment of the plaster;
• high energy costs due to heat loss;
• increase in humidity within the environment involved;
• excessively humid rooms;
• mold formation on wall surfaces;
• corrosion of metal elements present inside the walls; 
• ruined furniture;
• damage to health;

 

As already mentioned, the main cause is poor waterproofing of the foundations. Furthermore, it is a type of humidity often present in houses located on the lower floors (ground floor or basement). 

It occurs easily in ancient homes precisely because they often have load-bearing walls in direct contact with the ground, and also because the technologies and materials used were once unable to guarantee adequate waterproofing from the subsoil.  However, it does not spare even new ones if the waterproofing of the walls facing the foundations has not been carried out correctly. Furthermore, humidity can increase in the cold or rainy months, due to lack of evaporation.

In some cases the humidity is transmitted laterally, in fact in this case it is the ground on which the wall rests (the retaining wall) that transmits it. Also in this case the water penetrates the wall and rises via capillaries.

Typically it can be found in:

• Homes not raised from the ground
• Non-ventilated homes on the ground floor
• Homes located on underground floors without a ditch (this is the artificial creation of a void around the foundations of buildings used to prevent them from adhering to the damp ground and therefore preserve them over time);

The main cause lies in physical contact with the ground. After all, a building is mainly made up of stone materials such as concrete, bricks and the like. These can absorb and retain large quantities of water. Consequently, the more they are exposed to it, the more humidity attacks them. 

If the foundations have not been designed and constructed to minimize contact with the ground, moisture will abound. This often happens because the foundations are positioned with the soil also placed on their sides. Sometimes the ground floor attic rests directly on the ground, without ventilation.

The water causing rising damp can come from:

• groundwater tables
• stagnant rainwater
• water mains leaks

As already mentioned, it is the characteristic porosity of each material that characterizes the quantity of water, which moves inside it by capillarity, that it absorbs. This phenomenon occurs every time a liquid comes into contact with a fairly thin channel (called a capillary), in this way the fluid is able to travel up these capillaries reaching the external level, which can be both higher and lower than that of the liquid based on adhesion to the canal walls. 

The height of the humidity rise depends greatly on the quantity of water contained in the subsoil and on the degree of evaporation of the wall surfaces.

However, the rise time is counteracted by the effect of the force of gravity - which hinders the rise, delaying its effect - and directly depends on the exposure of the material to the air subject to the "evaporation" phenomenon whereby a equilibrium level of the water that rises without reaching the maximum possible height.

The diameter of the capillaries plays a crucial role in the rise of the liquid: the thinner capillaries will correspond to a greater rise and vice versa.

Another important factor that contributes to the phenomenon of rising water is the presence of salts dissolved in the water contained in the capillaries. As we said above, when water reaches the surface and evaporates, these salts crystallize; if this occurs on the surface, the classic visible white spots will appear, but if it occurs between the covering and the wall, the pressure of the crystallized salts will cause splits, detachments, swelling, etc.

Unfortunately, the ascent by capillarity is a continuous process if not stopped. Salts, given their hygroscopic nature (i.e. the ability to absorb water present in the atmosphere, giving rise to a hydrate or an absorption product, with related changes in size, appearance and colour), are the real cause of the damage to structures. In fact, their increase or decrease in volume, depending on the greater or lesser environmental humidity, causes the breaking of the capillaries, causing the chalking and crumbling of the plaster and in serious cases even of bricks, tuffs and the like. 

They even manage to keep the wall always moist on their own, even if there is no more rising water. Furthermore, it is almost useless to try to hide these stains by painting, as the salts would quickly resurface on the surface.

The localization of humidity derived from the subsoil is limited to the lower and underground floors, affecting the walls below ground level and the floors of the ground floor and underground rooms, with the corners joining the walls being particularly critical.

 

HOW TO RECOGNIZE RISING DAMP

It is not always easy to identify rising damp, also because initially it is a phenomenon that occurs internally. Furthermore, it is very slow in its manifestation because the plaster must be saturated with salts before it can be seen with the naked eye.

Nonetheless, once this occurs, unmistakable signs will appear:

• halos that rise from the floor upwards into the wall;
• appearance of mold and salt dust (if there is no salt dust present it is another type of humidity);
• chalking of plaster;
• musty smell;
• a dividing line (cordon) between the humid and dry parts, where the rising humidity rate is equalized by the evaporation rate. Usually this line does not exceed one and a half meters in height;
• Damp floors, walls and wall furniture;

It is very important to realize whether we are "really" in the presence of rising humidity or if, for example, we are in the presence of condensation humidity. In fact, it is the latter that is the most common humidity phenomenon. For example, it is very common in recent buildings, therefore waterproofed towards the ground, that rising damp from the ground is confused with other phenomena due to similar manifestations; in fact, many people forget that salts can also come from building materials. In these cases, rising damp is not caused by poor waterproofing, but by the condensation phenomenon that occurs at the base of the wall and then rises again.

There are signals that allow us to realize both. The answer is almost always provided by mold. In fact, precisely because it is a biological activity that prefers purer and slightly acidic water, such as condensing water, it is almost impossible to find it in rising humidity, which always brings with it salts that disturb it or inhibit its training.

Rising humidity forms a saturated solution of mineral salts on the surface, with a prevalence of sulphates, nitrates and chlorides, which is not compatible with biological formations. In fact, nitrates and chlorides are abundantly used in the preservation of cured meats and foods in general as they are natural antibacterials, furthermore domestic molds generally do not colonize on sulphates. In other cases, quite rare in reality, mold can be the consequence of infiltration of rainwater or damage to systems, i.e. water with very low or no salt content.

There are signs that allow us to distinguish rising damp from condensation:

• Domestic molds are almost always black or dark, and more rarely also green and brown;
• The salts present on surfaces in the form of efflorescence are predominantly white, in the form of adhering dust, fluff or filaments;
• the stain from rising damp is uniform, and proceeds from the floor upwards;
• the edge of the patch is well defined, and usually does not exceed a height of one and a half metres;
• the stain persists even when climatic conditions and relative humidity vary;

 

HOW TO INTERVENE AND HOW TO PREVENT IT

The best solution is obviously to prevent the occurrence of humidity by taking appropriate precautions. In fact, once it has occurred it is extremely difficult to eliminate it, so sometimes we simply "block" it, preventing it from causing damage in the short term.

Let's start first of all with what is best not to do when you notice the presence of rising damp:

Limit yourself to changing the plasters with more porous materials;

Hide the problem with covering products. Subsequently there will be greater problems and damage;

The elimination or reduction of rising damp can be achieved through two types of interventions, which are conceptually different:

1) INDIRECT INTERVENTIONS

These types of interventions do not affect the structure, but tend to reduce the supply of water from the soil to the structure, while simultaneously improving the evaporation of moisture from the structure itself.

2) DIRECT INTERVENTIONS

These are several possible interventions, such as:

• chemical interventions consist of drilling holes along the walls, horizontally, with an inclination of 12 mm in diameter, with a depth of approximately ¾ the thickness of the wall itself and 20 cm apart from each other. Special silicone or epoxy resins (they are thermosetting polymers with cold reaction) are injected into these holes - which must be previously stabilized - by means of slow diffusion transfusers, thus intercepting the entire section of wall involved. Finally, everything must necessarily be covered with a macroporous plaster. This is one of the most complete and least invasive interventions;
• mechanical interventions, consisting of cutting the masonry and the subsequent insertion of stainless plastic or metal materials as a barrier to humidity. Cutting is performed with a wall saw mounted on a trolley. It is very important that the wheels rest on a guide that can guarantee the constant cutting height in the wall. The cut must be made as low as possible so that the area under the cut remains wet. A roughened plastic sheet is inserted into the created crack and filled with mortar. In addition, the plasters are also replaced with other macroporous ones. This is a delicate solution and must be carried out with extreme caution and competence, as it could cause static damage if carried out incorrectly and roughly. Furthermore, it is a technique not applicable to retaining walls and prohibited by law in seismic areas. It is a technique feasible on brick walls no more than 50 cm thick. However, it is an obsolete technique as well as illegal, in fact in Italy it is expressly prohibited due to the structural damage it could cause and the seismic danger of our country;
• electroosmotic interventions, the water is sent back into the ground, which retains it, thanks to the artificial increase in osmotic pressure. This increase is carried out through the application of an electric field greater and opposite to the natural one (350 mV per linear meter against the natural 150 mV), which as mentioned sends the water back into the ground which will retain it. For its construction, desalination of the wall is carried out beforehand through an electro-osmotic washing system. Subsequently, electrodes are inserted across the entire width of the wall undergoing intervention, applying an adequate potential difference. The positive electrode will be inserted into the wall (outside or inside) at the same height as the stain. Instead, the negative electrode will always be inserted into the wall (external or internal), but at the lowest possible level, or alternatively in the cellar or under the floor. This is an effective method, but it can take a long time to see the effects. The drying process also leaves the salts inside the wall. When these soluble salts exceed a certain quantity, electroosmosis will be ineffective and the structure will have to be desalination;
• evaporating plasters, it is advisable to apply them as a completion of either the mechanical or chemical intervention. It is not advisable to simply apply evaporating plasters because they would only delay the problem over time, which in any case would recur without having prevented the cause. These are the so-called macroporous plasters, which are able to evaporate more water, taken from the wall on which it is applied, than the wall itself is able to withdraw by capillarity. This allows the surface of the plaster not to darken due to the presence of water waiting to evaporate. However, this capillary rising water always carries with it a certain percentage of dissolved salts, originally present in the soil and in the wall itself. These salts, depending on their concentration, sooner or later (usually it takes a few years, but it can also happen in a few months), crystallize in the macroalveoli where the water evaporates until it fills them. From this moment on, the salt deposited by the evaporating water, passing from the amorphous state (with a smaller volume) to the crystalline state (with a larger volume), will press on the walls of the alveolus until it disintegrates. This will happen almost simultaneously in all the alveoli, causing, as it actually happens, the sudden collapse of entire portions of plaster which will present a pulverized underlying layer beneath the compact surface. For this reason, its application is recommended as a completion of a more complete intervention. Furthermore, macroporous plaster cannot be used on internal walls due to the large quantity of evaporated water which would quickly saturate the air in the room;
• decontamination from all soluble mineral salts by simple physical extraction. This involves the use of compresses for the decontamination of brick or stone surfaces, historic plasters, floors, mosaics, etc. These compresses are composed of a pure, high-tech creamy paste in an aqueous environment, consisting only of pure cellulose fibers and diatomaceous siliceous earths. They do not contain sodium or chemical compounds. They are characterized by pH between 8.0 - 8.5. They are often used in architectural and civil restoration-conservation, as they do not have the disadvantages of clays (sepiolite, attapulgite, bentonite). It is easy to apply, non-toxic and non-flammable. They exploit the principle of micro-capillarity, having an internal porosity normally of around 0.3 microns, lower than that of most building materials. This ensures that, upon contact with the substrate, the saline solution is sucked in, which, once evaporated, will leave the salts inside the pack. You can therefore easily remove the compress with the absorbed salts, leaving the wall dry and clean. The disadvantages are the high costs and the expertise required for its execution, making it an expensive intervention;

To prevent its future manifestation there are some useful measures:

• create ventilated attics on the ground floor, or in any case where there is contact with the ground. If the attic, however, has already been built and rests directly on the ground floor, there is nothing left to do other than demolish it and then place elements that raise the attic, creating a ventilation cavity before pouring the screed on them. In this way the air will circulate and the humidity will be cut out;
• Reclaim the subsoil that will host the construction;
• Use lime-based and macroporous plasters,

There are three methods of measuring humidity in masonry, and all three are supported by European technical regulations (UNI):

• calcium carbide method, slightly polluting, slow and tiring for the operator, obsolete but quite precise;
• The second involves the use of a non-transportable laboratory and therefore turns out to be very slow and expensive given the technician's coming and going between the home and the analysis laboratory;
• The third method refers to the UNI11085 regulation and involves measurements using transportable equipment;