Goodbye to the Bricklayer's Trowel

Mortar pads are revolutionizing the brickwork in two apartment buildings in Knittlingen.

 

The lack of qualified specialist employees is one of many reasons why Franken Maxit (Azendorf, Oberfranken) began considering user-friendly ways of adhering bricks together. Tangible physical and economic advantages for architects and builders are even more important reasons to say goodbye to the mortar sledge and trowel. This is what happened in Knittlingen, a small community east of Karlsruhe. In just over a year, two apartment buildings have been built there with the bricklayers replacing their trowels a water hoses. This made it clear that maxit mörtelpads are suitable not only for traditional detached and semi-detached homes, but also for multi-story buildings.

 

Hardly anyone will get lost in Jahnstraße. It is located a little outside of the town centre of Knittlingen - in a quiet location - and the kind of street you can find almost everywhere:
Lined on the  left and right with simple, functional single-family houses, broken up a little by well-groomed gardens of flowers and vegetables. There's no historic architecture, neither are there any public buildings or restaurants. So it's a purely residential area. Nevertheless, two apartment buildings that are worth mentioning are currently being built. From the point of view of design, they stand out from the surrounding uniform standard, and those involved in the building use mortar pads as a technique that they expect to fundamentally revolutionize the current bricklaying practice over the next few years. But everything in time.

Getting to the point

The property provided space for two multi-storey apartment homes. The architect Gerd Bühler, who lives in the neighbouring town of Ölbronn, designed two clearly conceived, slightly elongated building cubes and created a wooden framed penthouse on the upper floor of each building????. This is a refreshing variation in the otherwise architecturally rather tedious environment of almost endless saddle roofs. The floor plans are clearly arranged: two apartments per floor, running from north to south away from a central, spacious staircase. The lift is located in the centre, with two sets of stairs running around it, with a cross podium providing access by foot to the floors.

 

The entrances of the two penthouses offer a touch of luxury, as both are directly served by the lift - the staircase here is rather the secondary entrance or an obligation for the health conscious. On the ground floor and first floor are two south-facing, spacious apartments with either a terrace or balcony. The penthouses offer the same floor plan - but everything is a little more generous. From the long living room and the roof terrace, you can enjoy an undisturbed view over Knittlingen and the Stromberg recreational area. Cooking and living are arranged in open plan in all of the apartments. The apartments on the ground floor also have disabled access.

Bricks as an energetic basic building block

Two basements plus a suspended penthouse with light weight wooden construction are intended for the brick building. The bricks in question come from come from the Schmid brickworks, which is just 30 km away in Bönnigheim. As a member of the Unipor Group, the brick manufacturer offers a broad product range with regard to statics, as well as sound and heat protection. The building owner, Pronath Immobilien GbR, was also quickly convinced by the monolithic design with brick walls, which is economic in the long term. Thanks to the "Unipor W08 Coriso" thermal insulation tile, a 15 mm thick lime plaster and 20 mm light plaster, the 36.5 cm thick outer wall easily achieves a U-value of 0.21 W / m2K on the outside. Together with the U-value of 0.17 W / m2K for the suspended wooden stand, the essential basic requirements for the achievement of the low energy transmission standard KfW 70 are fulfilled.

 

The energy balance sheet is supported by the energy-efficient, compact design of the buildings. For the interior walls, the options provided by the Unipor "system construction kit" were fully utilized: The partition walls of the lower floors are made of HLZ ground bricks of 11.5 by 24 cm, the increased soundproofing requirements for example for the apartment walls and lift partition walls are filled with concrete-filled brick shuttering tiles.

Grooves as an energy task

Over the past few years, brickwork has been gradually adapted and improved to the increased energy requirements: through the composition of the raw materials, the optimization of the chamber formations, or the filling of the chambers. Since the beginning of the increased focus on energy with regard to exterior walls, the bearings and butt joints are also being discussed. In the end, they were not to be overlooked because they showed up as sharp lines on every thermal image. The grout joints became thinner, the joints completely disappeared - in favour of toothed end faces.

 

The thinning down of the joints required two new requirements: The reduced tensile and compressive strength required a "reinforcement" of the glue joint, the increasingly large cross-sections became increasingly difficult to cover. Covering thin-bed mortar, as well as the mortar slides are the best answers so far, and: a qualified craftsperson is more important than ever. In Knittlingen, the architect and builder took a more innovative path and, together with the company Dürrwächter & Friedrich, which was responsible for the building shell, decided on the "mortar pad" developed by Frank Maxit (Azendorf, Oberfranken). The skilled craftsperson has remained, but the trowel has only rarely been used.

The moving water hose

The basic idea of the "mortar pad" is so simple that it is actually surprising that this development has not been initiated earlier. Franken Maxit approached the topic and developed a "mortar pad", which is applied dry to the moistened masonry and then only has to be watered. However, the solution to all technical problems, including obtaining the required building authority approvals, took several years. At the end of the development, pads composed of a light-weight mortar and a water-soluble hot-melt adhesive were created. Additional stability is provided by an integrated glass fibre fabric.

This new "mortar pad" from Maxit is a crucial advance on the previously established process with covering thin-bed mortar, After the water has been applied, the melt adhesive is hydraulically bonded and forms thin, full-area mortar joint of one to three millimetres. This setting process is carried out in the same way as conventional mineral mortars so that at the end of the process comparable structural values are achieved. There is no longer any need for mixing the mortar, transporting it over the construction site, etc. - only the water hose moves from stone to stone. "This system is clean all round, "explains Wilfrid Friedrich, Managing Director of Dürrwächter & Friedrich.

 

The ratio of the mixture of all components is precisely measured at the factory and it is not possible to use too much water. Maxit ensures this by means of the fact that the surface of the pads is structured in such a way that only the required amount of water can remain on it. Excess water runs off to the sides. "In principle, my bricklayers are almost overqualified for this technique," Wilfrid Friedrich continued. "I can rely almost blindly on the fact that the mortar mixture is correct and all joints are covered in full." A glance at the clean, uniform appearance of the joint of the finished brickwork in Knittlingen confirms this statement.

With regard to the strength and bonding properties, mortar pads are therefore laid evenly on a class M10 thin-bed mortar. It was also important to the client that the mortar pad is a purely mineral product, which originates from natural raw materials. The creation of a purely mineral exterior wall (mortar, stone, plaster) is easily possible in this way. In Knittlingen you can see what you do not see: A construction site without a trowel, a mortar sledge, and a mixer - tools that were formerly always seen of a construction site.

Energy efficient standards - a revolution in brickwork

In view of the revolutionary structural technology of the bricklaying, all of the other features of the building project appear like standards. Of course, a photovoltaic system is planned - installed on three-sides of the hipped roofs of the penthouses. An air-to-water heat pump will also provide a high level of energy efficiency. With a calculated annual heating requirement of 26.764 kWh, as well as an annual final energy requirement of 13.252 kWh, the two building cubes are also able to offer significant energy performance data. The laying of the masonry with prefabricated pads is, however, a quiet revolution in brickwork construction that is not visible afterwards. It will presumably be as standard in a few years as a photovoltaic installation is today in building technology.

Author: Dipl.-Ing. Peter Gahr