Horizontal waterproofing of terraces and balconies

Tired of seeing your balcony fall apart?

The problem of waterproofing flat parts is increasingly frequent in new buildings, since too much superficiality during construction and the now obsolete systems adopted to make them waterproof, have made the phenomenon of deterioration of the front panels or of the lower part of the balconies always more current.

Now it is possible to solve with definitive solutions both the problems induced by water in the above and below-level building structures, and the difficulties in conserving modern and historical wall structures, in the context of current environments.

The waterproofing system with Schlüter-DITRA

Schlü-DITRA is a waterproof polyethylene sheath capable of compensating for high vapor pressures. By laying the clamps at the joints and at the walls in a workmanlike manner, with Schlüter-DITRA it is possible to obtain perfect waterproofing according to the requirements of the ZDB (the German association of building manufacturers). Schlüter-DITRA therefore protects the substrate from damage caused by the penetration of water and any aggressive and harmful substances.


Schlüter-DITRA separates the flooring from the subfloor by neutralizing the transmission of the underlying tensions, which therefore do not transmit to the flooring. Schlüter-DITRA also acts as a bridge over the cracks, thus preventing them from reaching the surface layer.

Steam vent

The intercom channels on the back of Schlüter-DITRA allow the evaporation of the humidity present in the substrate and compensate for the vapor pressure.

Load distribution

Thanks to the square cavities filled with glue, Schlüter-DITRA transfers the loads present on the floor directly to the substrate; this is why the floors laid on Schlüter-DITRA are so resistant. In the presence of high mobile loads (for example in industrial environments) the tiles must however have a suitable thickness and resistance, as indicated by the prescriptions of the ZDB in force in Germany with regard to the laying of “Ceramic floors with high mechanical resistance”. In areas subject to high loads, the glue must completely fill the cavities between the sheath and the tile. In fact, it should be borne in mind that the contact surface between Schlüter-DITRA and the support is equal to about 50% of the entire surface, which can cause a decrease in the compressive strength of the tile in the case of high loads. It is appropriate to protect the flooring from impacts with hard objects. The size of the tiles must not be less than at least 5 × 5 cm.

Tear resistance

Thanks to the grip between the underlying fabric and the subfloor by means of adhesive and to the mechanical anchoring of the same in the square cavities, Schlüter-DITRA guarantees a good tear resistance between the floor and the subfloor (experimental laboratory values ​​approx. = 0.2 N / mm2 ). Schlüter-DITRA can therefore be used for both walls and floors. In the case of walls, if necessary, additional anchors can also be used.

The water drains and slopes

The problem of water drains and slopes of balconies / terraces is solved with special pieces, Schlüter-KERDI-DRAIN: a system consisting of a drain, a union and a dowel, which allow a perfect connection to a waterproofing. The use of waterproofing under coatings is an increasingly widespread practice and in Germany it is imposed by the certifications of the ZDB (the German association of building manufacturers).

Rising humidity and the chemical barrier

Rising humidity

The rising humidity occurs in the lower part of the walls. If adequate “protection and blocking” of the walls has not been prepared, the bottom of the structure draws water by capillarity along the micropores of the material, causing the detachment of the plasters and the tin coulters, the chalking of the surface parts of the materials stone and bricks, the formation of crusts and water-soluble saline efflorescence on the internal and external walls, the formation of algae and mold.

The main damages are listed as follows:

Static damage: over time the wall covering tends to detach itself, weakening the structure.
Economic damage: damp walls damage the building material, and greater damage corresponds to higher repair costs. A damp house loses up to 20% of the purchase value, requires higher heating costs (damp walls can lose up to 80% of their insulation capacity) and dehumidification.
Damage to health: the risk to the health of one’s family is very high due to harmful spores, an uncomfortable living climate with cold walls, favorable conditions for the birth and proliferation of pasassites and highly pathogenic agents. Furthermore, the not fully exploitable living space and the smell of mold negatively affect the well-being and quality of life of people and animals.

The solution: the chemical barrier

The chemical barrier consists in the interruption of the migratory flow of water in the masonry, through the impregnation of a layer of the masonry with products capable of inhibiting the capillary rise of humidity.

A series of circular holes of small diameter (10mm) are drilled, within which the water-repellent mixture is injected, and executed at a distance of about 10-15cm between them and for a depth varying with the thickness of the masonry. We usually intervene from the external side of the building about 15cm from the pavement. The physical principle on which the effectiveness of the chemical barrier is based is that due to a change in the meniscus of the water contained in the microporosities of the bricks and mortar where a rise in the water itself is no longer induced but instead its lowering.

This modification of the meniscus is in turn due to the effect of the siloxane resins carried inside and which, after impregnation, cover all the cavities of the receiving material. These water-based siloxane resins are transferred inside the pressure walls, i.e. behind automatic pumping until complete absorption by the wall.

Creation of the chemical barrier

The realization of a chemical barrier involves the creation of blind holes (pre-drilled holes) with diameters of 14-16mm using an electro-pneumatic roto-percussion drill. The injection is carried out using equipment consisting of a pumping unit, equipped with pressure gauges to keep the pressure constant, which varies from 0.5 to 0.8 atmospheres, according to the porosity of the masonry and other parameters, after which it is passed to the use of non-toxic and ecological formulations (siloxane resins) aqueous solution.

The preparation operations of the facing and the holes, together with the injection modalities, will have to be carefully planned and only after having carried out a preliminary inspection on the global situation and case by itself, since too many parameters influence the type of technological approach.

The resins, used to prevent the capillary rise of water, are non-toxic and totally safe both for the operators and for the inhabitants of the building. The substances used are organic derivatives of silicon, such as silanes and siloxanes. The two formulations that Dar.De.Ca. privileges in dehumidification works, they consist of a liquid silicizing concentrate that acts in depth, on a water basis and injected with a low pressure pump; the other product is a special silane / siloxane-based cream in an emulsion form that acts more slowly and from the surface, injected with a hand pump.

To complete the construction of the chemical barrier carried out, at least four finishing stages are required, necessarily carried out in this order:

closure of the holes used for the injection of the formulation;
flaking of dilapidated plaster;
cleaning and desalination of wall parameters;
restoration of plasters and paints.

The water-repellent action of the barrier chemical compounds starts already after a few hours, but in some cases it takes longer, due to the completion of all the chemical reactions essential for the complete cross-linking of the formulation. After this time, the injection holes can be closed with an anti-shrinkage mortar or resin (i.e. with low elastic modulus), compatible with the type of masonry and with the formulation used.

The complete dehumidification of the structure, above the chemical barrier, takes place in very long times: as an order of magnitude we can consider and estimate one centimeter of thickness per month. Even with good ventilation, almost continuous insolation and not very thick, the time required to dispose of the residual humidity can be several months, and during this period it is desirable (for a good result of the intervention) that on the vestments saline efflorescences appear (called “bleeding”).

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