Natural stone slab coverings in the outdoor area are timeless and accentuate both public areas and private gardens and courtyards. Due to their high design power, they can evoke very different effects with the type of stone, the laying pattern and the formatting, such as elegance, warmth, simplicity, luxury, aesthetics, generosity or down-to-earthness. In the past, many regions were strongly influenced by their locally mined natural stones, which were often used to make floors, walls, roofs and sculptures due to limited transport options.
This bauwion knowledge page deals with particularly common natural stones for outdoor use. Basically, there are many more natural stones that are suitable for outdoor use due to their formation and composition, i.e. frost-resistant and sufficiently weatherproof.
Material: In addition to the design properties (colour, format and laying pattern), the quality of the selected natural stone and the laying method must also be suitable for the individual situation.
Frost resistance is generally required for the use of natural stone outdoors in our latitudes. Weather resistance and de-icing salt resistance must also be taken into account depending on the load and location. Likewise, the bending strength or breaking strength of the material must be suitable for the expected load, depending on the format size and the plate thickness.
In addition, there is abrasion resistance, sliding and slip resistance due to the surface design, water absorption and porosity.
The possibilities of surface treatment and the cleaning and care effort of the respective natural stone material should be discussed with the client before the final decision is made. The respective manufacturer should be involved in the consultation, as the rock properties can vary greatly even within a natural stone family.
Trade names: Trade names of natural stones can be misleading. For example, "Jura marble" and "Belgian granite" are each limestone varieties and "Caribbean Blue" is mined in Scandinavia. The European standards DIN EN 12440 and DIN EN 12670 form the basis for uniform terminology and reliable information for the choice of natural stone. In addition to the trade names, other definitions must therefore always be included in invitations to tender:
Sizes and formats: Manufacturers of natural stone slabs always specify their products in nominal dimensions. The actual dimensions of a panel may deviate from these dimensions within specified tolerances. Boards with sawn edges must always be more dimensionally accurate than boards with split and pointed edges. The respective limit dimensions are specified in DIN EN 1341. The following types of boards are differentiated in the trade:
Surfaces: Outdoor floors need a certain roughness to promote slip resistance and slip resistance. For this reason, polished and ground surfaces are generally avoided. In the artisanal sense, various surfaces made with tools are possible, but also other processes such as flames, lasers, chemical treatments, etc.
Natural stones that are easy to split are offered with rough-split surfaces. See also encyclopedia article ►Natural stone surfaces.
Construction methods: The specific installation situation must always be taken into account when deciding on a laying system. These include the type of use, the use, but also the location of the floor surface. The client should be informed by the planner or the contractor with regard to the possibilities with the respective advantages and disadvantages.
In principle, care must be taken to avoid accumulation of moisture above and below the natural stone covering in the respective construction method. In the case of roof terraces, the Flat Roof Directive must also be included in the planning.
spacers: Spacers are used in order to maintain the required joint width evenly. In the case of format panels that sit at right angles to each other, these are usually joint crosses made of plastic, which are removed again after installation.
Colour differences: Natural stone slabs are natural products. Accordingly, colour nuances, different degrees of banding, veins and inclusions are to be expected and these are to be accepted to a reasonable extent. In order to achieve a harmonious look in the installation, it makes sense to view the panels beforehand and sort them if necessary. The targeted mixing of colour nuances in natural stone is often attractive in terms of design.
Movement and connection joints: Movement joints made of layers below the pavement, e.g. from the floor slab below, must be incorporated into the flooring in the case of bonded construction, see also lexicon article ►Movement joints in floor construction. The joint is covered either with a suitable elastic joint sealant or with a corresponding profile. The same applies to connecting joints, e.g. at the transition from the terrace covering to the house wall.
According to VOB C DIN 18332, a minimum width of 8 mm applies to movement, connection joints and building separation joints in outdoor areas.
Cleaning and maintenance: In the commercial sector, the manufacturer must provide the user with cleaning instructions in order not to jeopardize the slip resistance of the floor by incorrect cleaning methods or agents. In the private sector, the manufacturer is not obliged to do so. Nevertheless, at least a cleaning recommendation should be handed out that is tailored to the respective natural stone. This should be followed in any case to avoid mistakes.
For example, no acidic cleaning agents should be used on non-acid-resistant rock types (e.g. limestone, marble). Alkaline cleaners should only be slightly alkaline (pH < 10.5) to avoid matting surfaces. While alcohol cleaners may be used on hard rock, they can cause the surface to fade and gray on soft rock. In principle, the water hardness must also be taken into account for the correct dosage of the recommended cleaning agent.
The use of high-pressure cleaners is particularly critical for soft stone, as fine particles of the surface are detached here, which subsequently leads to even greater contamination.
Impregnation: While layer-forming sealants are not advisable outdoors (risk of frost damage if moisture penetrates), impregnation of the natural stone surface can make cleaning the surfaces easier and reduce soiling. Due to nano-effects, the impregnation protects in particular against stains such as oils or red wine, but does not provide protection against acids (e.g. in fruit juices, lemonades). Overall, impregnation makes it more difficult for dirt particles to adhere.
Impregnation does not lead to optical wet effects on the natural stone surface, but it does cause colour depressions to varying degrees, which is not always desirable. An uneven application of the impregnating agent can therefore also lead to cloud formation, especially in the case of very dark stones. A trial treatment is therefore useful.
Impregnations may only be applied to cleaned and dry surfaces. Since residual moisture, e.g. from mortar laying or cleaning, can only escape through the impregnated surface in the form of water vapour, subsequent drying takes a very long time and can lead to damage.
DIN EN 1341 Natural stone slabs for outdoor use - Requirements and test methods
DIN EN 1341/A20 Natural stone slabs for outdoor use - Requirements and test methods; Amendment A20
DIN EN 12058 Natural Stone Products - Floor Slabs and Step Coverings - Requirements
DIN EN 12440 Natural Stone - Criteria for the designation
DIN EN 12670 Natural Stone - Terminology
DIN 18318 VOB C Procurement and Contract Regulations for Construction Services - Part C: General Technical Contract Conditions for Construction Services (ATV) - Traffic route construction work - Paving surfaces and slab coverings in unbound design, edging
DIN 18332, VOB C Procurement and Contract Regulations for Construction Services - Part C: General Technical Contract Conditions for Construction Services (ATV) - Natural Stone Work End of forms
ZDB leaflets published by the Tiles and Natural Stone Association in the Central Association of the German Construction Industry (ZDB):
M FP - Leaflet for surface reinforcements with paving surfaces and slab coverings in unbound design as well as for edging, FGSV No. 618/1, Publisher: Verlag der Forschungsgesellschaft für Straßen- und Verkehrswesen
Working paper - Surface reinforcements with paving surfaces and slab coverings in bound design
[FGSV-Nr. 618/2], Publisher: Verlag der Forschungsgesellschaft für Straßen- und Verkehrswesen
Natural Stone Expert Talks, Series of the Magazine Naturstein, Publisher: Ebner Verlag GmbH & Co KG
Source: bauwion
