Masonry mortar

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Grout in exposed brickwork

The masonry mortar , i.e. mortar for the production of masonry , differs from plaster mortar in its current execution in important application properties . The various mortar manufacturers have matched the recipes and their properties to the application. The basic requirements for this factory mortar are regulated in Germany by DIN 18 557.

The starting materials for mortar production are binders, aggregates and additives or agents. These are added to the factory dry mortar at the factory and in accordance with the manufacturer's instructions. On the construction site, the required fresh mortar is produced in mixing machines that are mounted on the dry mortar silo, adding the amount of water specified by the dry mortar manufacturer.

Factory dry mortar

According to the former DIN 1053 ( masonry -DIN, withdrawn), masonry mortar is divided into three mortar groups (MG) and two subgroups according to the compressive strength of the masonry.

  • MG I (lime mortar)
  • MG II (lime cement / hydraulic mortar, 2.5 N / mm²)
  • MG IIa (lime cement mortar, 5 N / mm²)
  • MG III (cement mortar, 10 N / mm²)
  • MG IIIa (cement mortar, 20 N / mm²)

Since the stability and many other properties of the building depend on the various masonry mortars , the calculations and implementation guidelines are regulated in detail in the European "masonry" standard Eurocode 6 (DIN EN 1996-1-1: 2013-02). For example, only cements in accordance with DIN 1164 and calcium oxide (building lime) in accordance with DIN 1060 may be used as binders for the masonry mortar , but only binders in accordance with DIN 4211 (or similar binding agents approved by the building authorities) for combined plastering and masonry mortar. The sand used is also standardized in detail in accordance with the relevant DIN regulations in order to pass the building inspection approval and monitoring.

In contrast to ready-mixed concrete, dry mortar (also applies to dry concrete ) is not dependent on timely delivery and processing, but it should be used promptly, because it can be stored for a maximum of three to twelve months. Apart from the precisely matching addition of water, a constant mortar quality is guaranteed when using industrially premixed dry mortar even if the user has no specialist knowledge of mortar production and the mixing ratio of the aggregates .

Factory dry or factory fresh mortar with a dry density of less than 1.5 kg / dm³ is referred to as light mortar. The lower density is achieved through additives such as air entrainers or lightweight aggregates .

Of the various types of mortar, the most important and widespread are:

Facing mortar

Facing mortar is used for facing such as facing bricks , exposed masonry or exposed joints. Due to the different pronounced absorbency and water absorption of the stones used, mortars are offered for strongly absorbent ( water absorption over 10 % by weight ), for weakly absorbent (water absorption 4–10% by weight) and non-absorbent facing bricks (water absorption less than 4% by weight) .

The face brickwork filled joints is preferably carried out in a single operation to construction joints to avoid that can lead to local accumulations auffrierenden water. If even visible joints are desired, these can be e.g. B. can be carried out by wiping the joints with a piece of water hose. This smooths and compacts the mortar uniformly and reduces water absorption.

Facing masonry made of hard-fired stones such as clinker is often carried out as pure cement mortar (previous mortar group MG III).

Backing mortar

Backing mortar is usually referred to as the actual masonry mortar, as it is used in the actual masonry for butt joints and horizontal joints . Due to the different types of brick, a distinction is made here between lime, cement and mixed mortar. The mortar required in each case is prescribed by the stone manufacturer.

Lightweight masonry mortar

Light masonry mortars are also back masonry mortars according to DIN 1053-1. They are mainly used for bricking up highly insulating wall building materials (thermal conductivity around 0.2 W / (m · K)) in order to avoid thermal bridges in the joint area. If the difference between the thermal conductivity and absorbency of the mortar used and the brick is large, the joints can become apparent, especially with thin, single-layer plaster application. Most manufacturers of lightweight masonry blocks prescribe the use of a suitable mortar.

The bedding joint thickness corresponds to that of normal mortar. There are no requirements for the dimensional accuracy of the stones. Lightweight mortars have a less favorable deformation behavior than normal and thin-bed mortars under load. Masonry made from bricks, sand-lime bricks and concrete blocks shows a greater drop in strength than those made from aerated or lightweight concrete blocks. The differences in deformation do not have to be taken into account in the structural calculations of the masonry due to the small number of joints.

The dry bulk density of light mortars is reduced to less than 1.5 kg / dm³ by adding lightweight aggregates made from natural pumice , expanded clay or perlite. Light mortars are supplied as LM 21 (thermal conductivity calculated value λ 0.21 W / (m K)) and LM 36 (calculated value 0.36 W / (m K)) (for comparison: normal concrete 1.0 W / (m K)) K), highly insulating bricks 0.07 to 0.18 W / (m · K)). The difference results in an improvement of the masonry by one or two thermal conductivity groups overall .

Thin bed mortar

Thin-bed mortar is a normal mortar with a maximum grain size of about 1 mm, which is processed in a layer thickness of typically 1 to 3 mm. Only tiles, slabs, bricks and layout elements with deviations of less than 1 mm are to walling with suitable thin-bed mortar (z. B. flat blocks as Kalksandplanstein , aerated concrete block , hollow block diagram stone , Planziegel ). The strength corresponds roughly to the former MG III. The masonry strength as well as the thermal resistance of the masonry are higher than with traditional thick-bed mortar due to the lower proportion of joints.

Thin-bed mortar is often dosed and applied using special tools such as a toothed rail or mortar sledge . Another possibility is the so-called immersion process. The bottom of the stone is dipped into the thin-bodied mortar and then mixed. Compared to the mortar application with the mortar slide, the application quantity is somewhat less easy to control. In addition, a fabric fleece can be worked into the thin-bed mortar joint to improve the cover on perforated bricks. The application of the thin-bed mortar is colloquially also called "gluing" and represents an efficient process for high-quality masonry. Compared to thick-bed mortar, considerably less mortar is required on the construction site. Mixing, transport and application are therefore significantly cheaper.

In the back wall area, the thin-bed method is a frequently used wall method today.

Ready-made grout

Joint trowel

The usual way of laying fair-faced masonry is the fully jointed grouting of the butt and bed joints with a subsequent smoothing of the joint (also known as "walls in their own sap"). Alternatively, ready-to-use grouts are available for subsequent jointing. Here, the visible joints are scratched out up to a depth of 15 mm before the complete hardening process, cleaned and subsequently grouted with ready-made joint mortar and a special joint trowel. Prefabricated grouts in different colors are also available for the different facade designs.

Sewer and shaft construction mortar

This type of mortar is necessary for the high demands of sewer, manhole and sewer work and is treated with high-quality binders and mineral aggregates of mortar group III. But it can also be used for all other masonry and plastering work.

Roofing mortar

The roofing mortar is used to lay the hip and eaves tiles. The ridge tile is also laid with this mortar in the places where no ventilation ridge is installed.

The roofing mortar belongs to mortar group II and has a high level of adhesive strength and adhesion, as well as high elasticity . Roofing mortar is produced with the addition of cement-bound fibers and weather-resistant synthetic fibers in order to improve the adhesion to burnt stones and the water retention capacity. At the same time, even when it has hardened, it must meet the increased demands on the building roof in terms of tensile strength, elasticity and openness to water vapor diffusion.

Other dry mortar

Particularly for the construction and also the reconstruction of natural stone masonry, special mortars are required and are offered as grouting, filling and spraying mortars according to the individual requirements. These can also be used with the support of appropriate processing machines. A particular area of ​​application is mining , which requires specialized dry mortar.

A mortar in accordance with DIN 4242 is used to build glass blocks , as this must be more impervious. To use are binders according to DIN 1164, as Portland cement , Portland slag cement and slag cement. To improve workability (suppleness), hydrated lime according to DIN 1060 and trass according to DIN 51 043 up to a maximum of 20% of the cement content may be added. The compressive strength must be at least 12 N / mm² after 28 days.

Other dry mortars:

  • Various tile adhesives are used to lay tiles and floor panels.
  • Repair and sealing mortar
  • For small and winter construction work, special types of mortar are required, which, due to their composition and grain sizes, are classified as dry concrete.

Underpinning and expanding mortar is used to subsequently anchor components made of steel, stone or other pressure-resistant materials in existing walls, ceilings and other components. When renovating old buildings, swelling mortar connects newly installed bricks with the masonry with a force-fit connection . Underpinning mortar is another name for the same product when it is used, for example, in timber construction to level out unevenness between masonry, floor slabs or basement ceilings and the footsteps and wooden panel elements placed on them.

The need to use expensive underlay or swelling mortar as a standard and in new buildings is controversial. Use should be restricted to cases in which this is explicitly required by the structural engineer. Settlement damage is usually not caused by the use of ordinary lime and cement mortar (with a shrinkage rate of approx. 1%), but by defects in the execution or insufficient foundation of historical buildings.

The term “swelling mortar” is misleading, as most commercially available cement-containing swelling mortars do not actually swell, but merely set more or less without shrinking (see also: non-shrink grout ).

Only gypsum mortar generally increases its volume by approx. 1% when it sets and is therefore particularly suitable for grouting installation boxes and wall anchors. Since gypsum is not moisture-resistant, it should only be used indoors and in permanently dry walls.

Non-shrinking grouting mortar is also offered under the name swelling mortar . Pay attention to this when shopping, as grouting mortar is too liquid to be processed with a trowel.

Filling and injection mortars are used in building and monument renovation to strengthen existing walls by injecting masonry or to make them more impermeable for the purpose of draining masonry . They are often pressed into the hollow spaces between the stones with a membrane pump through “ packers ” (tubes with connecting nipples ) inserted into the wall .

Injection mortars usually consist of cement or other hydraulic binders and contain bentonite and rock flour as aggregate . Bentonite and other additives such as cellulose stabilize the suspension by delaying the settling of the solid components.

Injection foam mortars have recently been used to improve handling and to better adapt the compressive strength, density and elasticity of the injection mortar to the existing building materials.

Filling mortar are sold under a variety of names, such as grout , grouting mortar and plugging mortar , and in each case in combination with -mass or suspension instead of mortars . Filling mortars are often additionally formulated as swelling mortars to prevent shrinkage during curing.

Factory pre-mortar

Factory pre-mortar (also known as factory wet mortar ) is offered by ready-mixed concrete plants as a ready-to-use mixture. Since hydraulic mortars set too quickly, factory pre-mortar is only mixed as lime mortar of mortar group I. This can be stored on the construction site for a long time without hardening. With the addition of cement, the mortar can be converted into a mortar of MG II or MG IIa on site, with the amount and type of cement being specified on the delivery note by the manufacturer of the factory pre-mortar. The consistency (suppleness) required for processing can be adjusted by adding additional water .

Factory fresh mortar

The factory fresh mortar is an already premixed building material, which is produced ready-to-use by ready-mixed concrete plants using special vehicles (similar to the principle of ready-mixed concrete vehicles) and delivered to the construction sites. Due to its already existing aggregates, it can then only be processed for a short time (usually within 16 hours) and is therefore only used where this immediate processing is guaranteed. For these reasons, use in the DIY sector is rather an exception.

This factory fresh mortar also contains ingredients that delay the start of setting and setting in the unprocessed state. Therefore, in addition to the masonry DIN, this mortar is also subject to the standard for factory mortar (DIN 18 557), which regulates the admissibility of certain additives and special binders , but also the regulations for the forms of delivery in a list of types, which must be recorded on the delivery notes.

Important contents of such a list of varieties are therefore:

  • Type of binder and aggregates
  • the assignment to a mortar group according to DIN 1053 Part 1 and Part 2
  • the application guidelines according to DIN 18 550
  • the variety number
  • the type of effect of the additives (delay times, etc.)
  • additional properties (e.g. water-repellent, water-repellent, etc.)

Furthermore, the fresh mortar has to fulfill a contradicting property, in that it should remain soft in the mortar container for a long time, but should harden very quickly after being introduced into the masonry. This peculiarity is called green stability and is achieved through the coordinated addition of additives by the manufacturer. He must of course know beforehand what type of masonry the mortar is to be used for, in order to take into account the different strengths, climatic conditions and the stones used on the building site.

Construction site mortar

Recipe masonry mortar according to DIN V 18580 and DIN V 20000-412

Normal masonry mortar may be produced on the construction site according to the mixing ratios given in the table without further proof of suitability or conformity .

Normal masonry mortar according to Annex A of DIN V 18580 and DIN V 20000-412 (DIN EN 998-2) (details in room parts)

Mortar grade previous mortar group Lime dough Hydrated lime Hydraulic lime (HL2) Highly hydraulic lime (HL5) cement sand
M 1 MG I 1 - - - - 4th
- 1 - - - 3
- - 1 - - 3
- - - 1 - 4.5
M 2.5 MG II 1.5 - - - 1 8th
- 2 - - 1 8th
- - - 3
M 5 MG IIa - 1 - - 1 6th
- - - 2 1 8th
M 20 MG III - - - - 1 4th


  • Instead of highly hydraulic lime, plaster and wall ties (MC5) can also be used.
  • The sand should consist of natural rock. The quantities given relate to the moist condition when stored.
  • The DIN 1053-1 for masonry with the division into mortar groups (MG) was withdrawn at the end of 2014.
  • The mortar classes (M) are determined according to DIN EN 998-2; the minimum requirement for compressive strength according to DIN V 18580.
  • As a special form of hydraulic and high-hydraulic lime (HL and HL 2 for 5 engl. Hydraulic lime ..) in are refurbishment and Preservation also , of course, hydraulic limes employed, the analog and NHL 2 , NHL 3.5 and NHL 5 are referred to. These already contain the starting material, i. H. the limestone used , minerals that act as hydraulic factors or pozzolans after firing , so that these do not have to be added separately.



  • Cement-lime-gypsum , trade journal for the entire binder industry and its suppliers from the mechanical and plant engineering sector, publisher: Bauverlag BV Berlin GmbH

Web links

Individual evidence

  1. Lightweight mortars and light plasters - Ecobalance , Forum | Sustainable Building; accessed in January 2017
  2. Other information on thermal conductivity: λ R 0.16 W / (m K) (Klaus Usemann, Horst Gralle: Bauphysik: Problems, tasks and solutions , p. 39, W. Kohlhammer Verlag) and λ 10tr 0.18 W / (m · K) (data sheet LM 21 from Quickmix); each accessed in February 2017
  3. Other information on thermal conductivity: λ 10tr <0.27 W / (m · K) ( data sheet lightweight masonry mortar LM 36 , from Quickmix). Example formulation of light mortar LM 36 (in% by mass): 40% cement, 3% white lime hydrate, 10% limestone sand, 15% limestone powder, 32% expanded clay or pumice, 0.030% methyl cellulose, 0.015% air-entraining agent, 0.020% adjusting agent ( light mortar and light plaster , Forum Sustainable Building). Accessed in February 2017
  4. ^ Entry types of mortar in the online lexicon "Baunetz Wissen" of the architecture magazine BauNetz; accessed in January 2017
  5. Discussion about non-swelling swelling mortar in the forum, accessed in May 2016
  6. One exception seems to be the swelling mortar from Baumit, whose data sheet ( Memento from June 21, 2015 in the Internet Archive ) stated a volume increase of 10%, accessed in May 2016
  7. Report on confusion between swelling mortar and grouting mortar by building material dealers, private construction diary, accessed in May 2016
  8. Sylvia Stürmer: Injection foam mortar for the renovation of historical masonry with special consideration of building-damaging salts . 1997, urn : nbn: de: gbv: wim2-20040311-761 .
  9. Use of masonry mortar without suitability test (recipe mortar) , Internet offer of HeidelbergCement AG, Germany; accessed in February 2017