Horizontal barrier

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A horizontal barrier or horizontal sealing prevents as part of the structural waterproofing the soil moisture from the masonry capillary rise (see also: Rising humidity ). In the base masonry of new buildings, DIN requires at least one horizontal barrier at least 30 cm above the surface of the earth, in the case of new hives with a cellar a further 5 cm above the finished basement floor and a third below the basement ceiling, provided this is at the level of the surrounding soil. In older structures, there are often no barriers at all or they are no longer sufficiently tight. Subsequent horizontal barriers are then usually essential in order to dry out the masonry .

Example of a possibility for sealing in old buildings by drilling
on the left clearly the damp masonry without a lock

Rising moisture in the wall leads to various moisture damage :

  • dark or cloudy color changes and light edges, which mark the extent of the moisture penetration,
  • Wall paint peeling off in the outside area, crystallization of salts as well as long-term sanding and peeling wall plaster,
  • Mold or sponge infestation indoors .

With increasing humidity, the thermal conductivity improves (the ability to heat insulation deteriorates). A reduced interior wall temperature as a result can lead to the formation of condensation on the wall surface in winter and to a further increase in moisture penetration.

Execution for new buildings

Sanded bitumen sheets or robust foils are mostly used as a horizontal barrier when building new walls . These are usually embedded in mortar on both sides in order not to be damaged by the bricks. It is important to ensure that the strips overlap sufficiently at the joints. In buildings with a basement, two or three horizontal barriers are often installed: The first is about 5 cm or a layer of stone above the floor slab. This distance from the floor slab prevents water that has accumulated on the floor slab during the construction phase or as a result of a later damage from being able to wet the entire wall. The uppermost barrier layer is approx. 40 cm above the edge of the terrain. This prevents the moisture penetrating the wall in the splash area of ​​the building base from being able to pull further upwards. If a floor slab is in the area of ​​the basement masonry or in the splash area of ​​the building base, another barrier layer is provided about 5 cm below the ceiling.

Old buildings

In old buildings, attempts were made to reduce the rise of moisture in the wall by using dense natural stone or hard-burnt clinker in the base masonry, as well as through continuous barrier layers of slate and later also of roofing felt and bitumen sheeting. However, the roofing membranes were often too thin to be able to block off the moisture permanently. Even when using thick bricks, a certain amount of moisture could rise through the mortar in the wall joints.

Subsequent horizontal lock

Depending on the degree of moisture penetration , load case according to DIN 18195 , accessibility and the structure of the wall, various methods for the subsequent installation of a horizontal barrier are possible.

  • For mechanical horizontal sealing, a barrier layer made of cardboard, stainless steel sheet, plastic sheets or foils is inserted into the wall cross-section to prevent the water from rising.
  • For chemical horizontal sealing, suitable substances are injected into the masonry in order to reduce the spread of moisture.
  • In the electrophysical dehumidification is electro-osmosis , trying to prevent the moisture effects in the masonry. Its effect is controversial.

Wall saw process

With the wall sawing process, the masonry joints are cut open in one level in sections of about one meter each with sword, circular or wire saws so that PE fiberglass or stainless steel sheets can be inserted. The panels are then wedged force- fit over the entire cross - section of the wall , the joint is spread with mortar and the remaining cavities are grouted with swelling mortar. Such mechanical locks are reliable and effective over the long term. If the floor slab is also to be subsequently sealed, it is advisable to construct a continuous trough by pulling the sealing sheets in the floor up to the sealing level in the wall and connecting them to the slightly inwardly protruding sealing plates in the wall.

Wall replacement process

The bricks of one or two levels are cut out of the masonry over a length of up to one meter. After inserting a film or bitumen sheet into the gap that has arisen, the stones are walled in again. To avoid settlement cracks , the grout should be compacted or swelling mortar should be used. After the grout has hardened, another meter of the old masonry is carved out. This procedure is quite simple to carry out, but comparatively time-consuming. The load-bearing capacity of the wall should be assessed beforehand by a specialist in order to determine the possible length of the section to be removed and to avoid cracks caused by sagging masonry.

Hammering in sheet metal

Chrome steel plates hammered into the joint under the last row of bricks. Condition before plastering the base.

If the masonry mortar does not consist of pure cement mortar , stainless chrome steel plates ( stainless steel ) can be driven directly into a bed joint. Without having to remove the mortar, an approximately 1.5 millimeter thick sheet of corrugated iron is hammered in. Since a continuous mortar joint is required for this, the method cannot be used on natural stone walls, which are usually made of stones of different heights. If you are working from the inside, it is difficult to drive the sheets into the outer corners of the masonry. Settlement hardly occurs because the slabs are driven in without opening the mortar joint. The joint mortar is displaced up and down or compressed. The vibrations of the blows, usually generated with the help of a special device, can cause subsidence and cracks in previously damaged masonry. In order to accelerate the driving in, chrome steel plates are also used, which are tapered on one side.

Drill core process

In this process, core drillings with a diameter of eight to ten centimeters are lined up in an overlapping manner and then filled with an impermeable mortar. Since the drill holes are set so that they intersect, a continuous barrier layer can be created.

Injection method

In order to prevent capillary moisture transport in the masonry, a sealing curtain is injected into the masonry. Holes with a diameter of at least 10 mm are drilled at a distance of about 10 to 25 centimeters to a depth of at least 2/3 the wall thickness. The holes usually start in the middle of a brick and lead downwards at an angle to penetrate one or two bed joints . The bed joints are usually more porous than the bricks, so that the injection material is initially distributed in the plane of the joint over the entire cross-section of the wall and then ideally moves evenly into the bricks below. The injected material is intended to permanently clog the pores of the masonry or to make the walls of the pores water-repellent with a hydrophobic "coating". This means that capillary water transport can no longer take place and the masonry above can dry out.

A distinction is made between processes with and without pressure. In the first case the injection material is pressed into the masonry with up to 13 bar pressure, in the second case it penetrates into the pores of the masonry under the action of gravity and capillary force.

Irregular natural stone masonry cannot be reliably sealed with low-viscosity injection agents. The masonry joints are often not regularly in one plane. Even natural stones, which were carved into blocks on the visible side, are generally very irregularly shaped on the side facing the inside of the wall. Typically, the gaps that remain between the stones when the wall is built are unevenly filled with broken stone and mortar. Large quantities of the liquid injection agent can collect in the cavities that remain here and seep downward without a continuous barrier layer being formed. In order to remedy this problem, the holes are used to first press injection mortar (also known as filling , grouting or grouting mortar ) into the inside of the wall. Before the injection compound has completely set, the sealant is then pressed in. This prevents the sealant from seeping down. Instead, it penetrates the injection mortar and is evenly distributed in all three dimensions. Since the sealant is usually many times more expensive than grout, this method is more economical than grouting with sealants of a gel-like consistency. The latter are now being offered by various companies to limit the seepage of the sealant.


For as silicification methods known alkali metal silicates used; these can also be introduced without pressure or with low pressure. The application may have to be repeated after a few years. Silicification products are alkaline and bear the “caustic” hazard symbol. Handling them therefore requires the necessary caution and the use of appropriate protective clothing.

If heated liquid paraffin is used as an injection substance, this has a pore-clogging effect. There are also paraffin oils with plastics dissolved in them. Silicone microemulsions, on the other hand, have a hydrophobic effect.

Dyed injection materials are also available so that the distribution of the material can be checked with the help of control holes.

The introduction, the mode of action and the application limits of the process and the various injection materials are described in the WTA leaflet 4-4-04 / D " Masonry injections against capillary moisture" published by the Scientific-Technical Working Group for Building Preservation and Monument Preservation . The leaflet points out, among other things, that not every injection material can be used universally, but the injection of the various injection materials depending on the degree of moisture penetration, the capillarity of the building material and the thickness etc. must be planned and used specifically for the building material in order to achieve success. According to the WTA information sheet, the manufacturer of the injection substance can obtain a WTA certificate from a test center. If the injection material passes the test conditions, it then receives a so-called WTA effectiveness test certificate stating the degree of moisture penetration of the injected building material for which it has passed the test.

Procedure with high moisture penetration

The degree of moisture penetration of the masonry and the resulting amount of injection material are decisive for the efficiency of a pressureless borehole injection. However, if a building material pore is filled with more than 95 percent capillary water, for example, there is insufficient residual volume to be able to absorb injection material. An injection into such a soaked building material is therefore ineffective without preparatory measures. H. the pores must first be freed from the water. This can be done by what is known as pre-drying, which precedes the actual injection. Electrically operated heating rods are inserted into the drilling channels and the masonry is heated to a temperature of around 110 ° C. During this heating process, the water present in the pores of the building material evaporates in the area of ​​the later injection level. During the subsequent injection, the entire pore volume is available for the pressureless absorption of the injection substance. Predrying is necessary, for example, so that the building material can absorb paraffin oil.

Electroosmosis process

The electroosmosis process is not a horizontal barrier in the narrower sense, but is based on the physical principle of electroosmosis according to the information provided by the provider . The corrosion resistance of the lines has been confirmed by scientific studies (e.g. BAM 2/18776) and is contained in ÖNORM 3355-2. More information can be found under the heading Electrophysical Wall Drying .


  • Subsequent mechanical horizontal barriers. In: Leaflets of the Scientific-Technical Working Group for Building Preservation and Monument Preservation. No. 4-7-02 / D.
  • Masonry injection against capillary moisture. In: Leaflets of the Scientific-Technical Working Group for Building Preservation and Monument Preservation. No. 4-4-96 / D.
  • Frank Frössel: masonry draining and cellar renovation. IRB-Verlag 2001, 2nd through. Edition 2007, ISBN 978-3-81676-126-6 .
  • Frank Frössel: Lexicon of building sealing and cellar renovation . Baulino Verlag 2005, 1st edition 2005, ISBN 978-3-93853-705-3 .
  • Frank Frössel: Textbook of cellar renovation and sealing. Expert Verlag 2006, 2nd edition 2009, ISBN 978-3-81692-757-0 .
  • Jürgen Dreyer: Basics of building physics.
  • Edmund Bromm: Healthy living in old buildings. Pro Literatur Verlag, 2007.

Web links

See also


  1. a b c M. Boos: Injection materials for subsequent chemical horizontal barriers , In: Old building renovation 8: Measuring, planning, executing 24 - Hanseatische Sanierungstage Heringsdorf 2013, p. 119ff, published by BuFAS e. V., Fraunhofer IRB Verlag, Beuth Verlag GmbH