Plan stone masonry
Plane stones are artificial, particularly precisely manufactured bricks made of various materials. The bearing surfaces of the flat stones are more precise and parallel, so that they can be offset using thin-bed mortar or plastic adhesives (PU, PUR). The butt joint is usually toothed without mortar. The material can be sand-lime brick , aerated concrete brick , hollow block flat stone or brick (then called flat brick ). In the case of hollow blocks and bricks, the bearing surfaces are ground flat after the concrete has hardened or the brick burns in order to achieve the required accuracy and evenness.
Mortar joint
While the conventional back wall stone is processed with a 10 to 12 mm thick normal or light mortar bedding joint ( mortar bed ), the thickness of the thin bed mortar joint is only 1–3 mm. This results in a flat stone height of an average of 249 mm compared to the conventional brick of 238 mm. Both bricks add up to the respective mortar thickness to give a layer height of 250 mm.
The thin-bed mortar is applied to the flat stone using a notched trowel, mortar sledge or by immersion . With perforated bricks, there is the option of covering the thin-bed mortar in order to prevent air circulation. In addition, a fabric fleece can be worked into the horizontal joint to improve the cover. Due to the low mortar thickness (approx. 2 mm), increased demands are placed on the permissible tolerances (± 1.0 mm) in height on plan stones. The plan stone manufacturers offer a specially tailored thin-bed mortar to match their stone. Since around the end of 2015, load-bearing walls have also been allowed to be walled up with a special PU adhesive under certain conditions. Meanwhile, there are also manufacturers of precast elements who produce wall panels with a special PU adhesive.
Masonry association
The prerequisite for the use of plan stones is the careful production of the first layer of the masonry bond. To compensate for the height, either special paring stones or flat stones are laid in masonry mortar (mortar group III). In order to reduce the thermal bridging effect of the lowest stone layer, the manufacturers meanwhile offer kining stones made of special materials, which have the effect that the heat losses in this area are lower. These special Kimmsteine are mostly used in sand-lime brick masonry. The creation of the first layer must be carried out with particular care (checking the evenness in the longitudinal and transverse direction), as later height compensation in the layers above is hardly possible.
Insulation and soundproofing
Flat bricks are made as vertically perforated bricks, with the brick webs forming perforated chambers (Fig. 1) which trap air. After the firing process, large-chamber bricks (Fig. 2) are mechanically filled with insulating material. Due to the small amount of joints and the optimized material properties of the bricks, insulation values are achieved with which single-shell wall constructions can be achieved without additional layers of insulation material in accordance with the requirements of the applicable EnEV.
In order to produce soundproof bricks, for example for partition walls, backfill bricks are also made as block or flat bricks (Fig. 3). These take on sound-related tasks and are not filled with insulation material, but with heavy mortar or concrete after the storey-high wall has been completed. Ground-level backfill bricks complement each other in practice, on the construction site, thanks to the same height as the layers, optimally with the level bricks of the external masonry.
advantages
Advantages of the flat brick in combination with thin-bed mortar:
- Less mortar is needed.
- The thin mortar joint in the masonry causes a significantly reduced thermal conductivity through the masonry.
- Single-shell wall constructions without the use of additional insulation layers are possible.
- The less mortar is used, the less moisture there is in the masonry.
- The application of the thin-bed mortar takes less time than bricklaying with classic mortar and a thick mortar joint.
- The plane-parallel ground surfaces in the area of the bed joint and the thin mortar layer create a non-shrinking and homogeneous substrate for the plaster to take up.
- The load-bearing capacity of the wall (masonry compressive stress) increases compared to block bricks with lightweight masonry mortar (LM 21, LM 36).
Terms and standards
Depending on the type of stone, different terms are used in the respective product standards:
| Type of stone | standard | term |
|---|---|---|
| Hollow block as a plan stone | DIN EN 771-3: 2015-11
DIN EN 771-5: 2015-11 |
Plan hollow block
Plan full block / plan full block |
| Sand-lime brick | DIN EN 771-2: 2015-11 | Plan stone / plan element |
| Aerated concrete | DIN EN 771-4: 2015-11 | Plan stone / plan element |
| Bricks , usually perforated bricks | DIN EN 771-1: 2015-11 | Plan brick |