- The destructive effect of moisture
- Reasons for the accumulation of water in structures
- Water repellents and their principle of action
- Penetrating hydrophobization of concrete
- Surface agents
- Where the use of water repellents is useless
High humidity is a major risk factor for most building materials. To combat this phenomenon, a wide range of agents have been developed, one of which is water repellents. We will reveal in detail the topic of their choice and use in the construction of stone buildings..
The destructive effect of moisture
The main reason for the loss of strength and integrity of building and finishing materials is the permanent presence of condensed moisture in their thickness. There are several main mechanisms of exposure that lead to various negative effects..
Frost erosion is the main reason for the loss of monolithic strength. Particles of water trapped in the structure of the material freeze at low temperatures and increase in volume. This leads to disruption of structural bonds and an increase in porosity. Over time, the material accumulates water in ever larger volumes, which is why the negative effect of freezing increases many times.
Water is destructive and liquid. Materials such as aerated concrete and low-grade cement mortar are destroyed by chemical reactions in the presence of water. Ultimately, the negative effect is expressed in the loss of chemical properties of binders; gypsum-based materials are especially vulnerable in this regard. In the process, a concomitant negative effect arises – a violation of the surface aesthetics due to the formed efflorescence.
A sharp increase in thermal conductivity can also be distinguished from the main negative effects of high humidity. Water is the best known conductor of heat, its accumulation in building structures leads to a significant decrease in the energy efficiency of the building. The effect is enhanced in the outer layers when moisture freezes – in a solid state of aggregation, it conducts heat many times more intensively.
Reasons for the accumulation of water in structures
Water is an integral part of the ecosystem and therefore it is impossible to completely exclude its impact on construction projects. Nevertheless, it is quite possible to reduce moisture accumulation to reasonable limits, for which you need to know the main ways of moisture penetration into building structures.
The most obvious of these is the direct hit of atmospheric precipitation on the surface of the walls. The structure of some building materials implies rapid weathering of moisture within several tens of hours after getting wet, which almost completely eliminates the negative effect. However, in some cases, moisture evaporates from the surface of the cladding or plaster very reluctantly, penetrating deep into the hygroscopic structure more and more.
Another way is capillary suction from the foundation or puddles accumulated on the blind area. Under the influence of surface tension, water rapidly spreads inside materials that have at least some pronounced porosity, even with a closed cell structure. To reduce this effect, the water absorption of concrete structures is reduced, horizontal cutoffs from the waterproofing are arranged, although it is extremely rare to completely get rid of capillary movement..
The third way is condensation of moisture coming from inside the building. Materials with high vapor permeability must be protected by special membranes to prevent water vapor seepage. However, in practice, the calculation of walls for moisture accumulation and displacement of the dew point is not always carried out. Because of this, water vapor freely penetrates through porous materials and condenses in the finishing layer, causing cracks and delamination of the coating over time..
Water repellents and their principle of action
To understand how moisture penetrates and accumulates in various environments, you should at least superficially familiarize yourself with their structure. The presence of pores is characteristic of almost all building materials with the exception of plastic or metal. The porous structure forms a labyrinth of capillaries, along the surface of which water can move very long distances.
The efficiency of moisture spreading depends primarily on the ability of the inner surface of the capillaries to be wetted, that is, to retain a water film. The larger the area of this film, the faster and more intensively the water spreads through the structure. One of the methods to combat this phenomenon is used for waterproofing, which simply clogs the pores of the material, turning it into an insurmountable barrier to liquids and gases..
The principle of action of water repellents is different. They modify the surfaces formed by the structure of the material in such a way that more than one water molecule cannot adhere to them. In other words, a particle of water vapor can briefly “stick” to the capillary wall, but this excludes the possibility of the attachment of a second particle and, as a consequence, the possibility for moisture condensation disappears.
Penetrating hydrophobization of concrete
One of the most well-known hydrophobization agents is sodium methylsiliconate. It is one of the oldest concrete admixtures and is also used as a penetrating waterproofing barrier. According to the principle of action, sodium methylsiliconate occupies an intermediate position between waterproofers and water repellents, limiting the movement of moisture into the depths of the material by lengthening the labyrinth formed by the pores, as well as preventing the effective wetting of surfaces.
Also, materials based on silicone and rubber have become very popular as impregnations for concrete. Unlike penetrating waterproofing, such protective agents impregnate only the upper layers of the surface, forming an external waterproofing. The essence of the effect is that the surface can attach only a limited number of water molecules, which does not allow the surface tension forces to increase to those values at which capillary movement is possible.
The most important difference between water repellents and penetrating waterproofing is the complete absence of gas exchange disturbances. Due to this, the rapid weathering of the remaining water that has managed to penetrate into the surface layer is ensured, and nothing prevents the passage of water vapor from the inside of the premises in a natural way.
In contrast to agents that penetrate deep into the material, surface water repellents practically do not modify the porous structure. Instead, they form a complex web of crystalline formations or polymer chains on the surface, which prevent moisture from accumulating in large quantities. Unlike volumetric water repellents, surface water repellents do not protect against capillary suction from the foundation side and practically do not contribute to the displacement of moisture from the wall.
Cationic surfactants are often used as surface water repellents. The effect of their use is not only the formation of a water-repellent film on the surface of the material, but also giving it bactericidal properties. Due to this, the formation of mold or overgrowth with moss is completely or partially excluded..
Also, for surface application, a wide range of construction chemistry has been developed, based either on compounds of salts of some metals, or on organosilicon substances – modifications of silicone. The most popular solutions of potassium alkyl siliconate are the only group of water repellents that can be diluted with water. These are the cheapest and easiest formulations to use..
Another group of organosilicon chemistry is technical silicone concentrates, which are diluted before use with organic solvents up to 50-100 times. The technology of using such water repellents is more complicated, but they do not allow the possibility of acquiring a fake under the guise of an original product, and are also characterized by a longer service life..
Where the use of water repellents is useless
Unfortunately, not all building structures can be limited in water absorption by means of hydrophobization. First of all, this applies to materials with high porosity, such as shell rock or “warm” aerated concrete. To protect them, a protective layer with a denser structure is required, which is subsequently treated with a hydrophobizing agent..
Also, water repellents must be used with great care to protect structures containing steel reinforcement. The high alkalinity of most products contributes to increased corrosion processes and reduced durability. Therefore, for plaster reinforced with mesh, as well as for reinforced concrete structures, only the use of impregnations based on organic solvents that do not form caustic alkali metal salts during the hydrophobization process.