When preparing for the formation of a PAVING or WALL COVERED by natural stone, it is essential to have a perfect knowledge of the support, i.e. of that structure, horizontal or vertical that will be completed with the application of natural stone.


The support can be made up only of load-bearing elements but much more commonly it also includes other layers having different functions.

The loadbearing layer

In traditional constructions the main types of load-bearing layers that make up internal horizontal supports are: mixed brick-cement slab; cast-in-place reinforced concrete slab; slab with prefabricated concrete panels also light type ("predalles"); floor with prestressed prefabricated elements and brick; steel slab; mixed steel and brick slab; wooden slab.
The most common load-bearing layers of external horizontal supports are: ballast; cast-in-place reinforced concrete.

The other layers

With reference to the standard UNI 7998:1979 “Building. Floorings. Terminology.” and UNI 8381:1982 Building. Flooring support layers. Instructions for design and execution.” the presence of the supporting layers interposed between the load-bearing layer and the walking surface must be taken into consideration, such as: draining layer, regularization layer, levelling layer, slope layer, separation layer, stiffening layer, system integration layer, waterproofing layer, thermal insulation layer, insulation layer, as well as specifically for stone pavings:

Stone covering layer
it is the surface finish consisting in the stone elements. This layer must be installed with the utmost care, as this work consists in what the user will enjoy and see.

Installation bedding layer
placed in a position immediately below the paving elements, it has the function of binding the stone to the underlying layer, for example for interiors in a cement screed (which often acts as a regularization + levelling + system integration layer) or for exteriors in a reinforced concrete casting (acting as a load-bearing layer). The bedding can be composed of cement mortar and have a thickness of several centimetres, or by adhesives of various nature for a thickness of a few millimetres and never greater than one centimetre;

Foundation layer
The installation foundation is the surface of the layer immediately below the mortar or adhesive bedding layer that must guarantee a solid adhesion. For example, it may consist of the loadbearing layer slab surface or of the levelling layer surface, or, in the case of exteriors, of the stabilized ballast surface or of the reinforced concrete casting.

A good foundation is the essential prerequisite for any paving: it guarantees the adhesion of the mortar or adhesive bedding, distributes the concentrated loads to the underlying layers avoiding local yielding and alterations, reduces the risk of fractures or cracks and preserves the integrity of the paving over time.
Example section view of a roadbed
Example section view of a roadbed
Example section view of a roadbed


the typical foundation for outdoor paving

The importance of the foundation is significant for outdoor stone pavings, especially when intended for the transit of vehicles, as it is commonly identified with the same load-bearing layer, thus including in itself both the structural function and the guarantee of stability and solidity of the entire construction.
In ancient times the presence of the foundation was replaced by the use of heavy solid ashlars laid and beaten manually on layers of selected aggregates, the "Macadam" foundation, still used today for the construction of driveways, derives from this practice.

The foundation which is undoubtedly more use today, both for public and private constructions, is however the reinforced concrete foundation: a mixture of sand or gravel, water, cement in the minimum dosage of 200 kg/m3 cast-in-place by embedding sheets of electrowelded iron mesh having cross-section of min. 6 mm and 20x20 cm or 10x10 cm mesh. The thickness of a reinforced concrete foundation is commonly between 10 and 15 cm for light and occasional transit (for example foundations for private homes) or higher thickness for public roads according to precise design calculations.
The construction of this kind of foundation is absolutely the most suitable for outdoor natural stone paving.

The possibility of obtaining a state-of-the-art paving depends on its correct construction, after the preparation of a sufficient and effective slope for the disposal of surface waters: slope of at least 1.5 cm for each linear meter (1.5 % or higher), with an adequate amount of water collection and disposal points in suitable positions.
The foundation is almost always the main responsible for localized fractures on the surface of the stone paving, it is therefore advisable to adequately compact the underlying layer before performing the casting operation, avoiding as far as possible successive casting operations and respecting its drying and settling period (28 days) before starting the installation of the stone elements.

Useful installation thickness

The construction of a foundation must necessarily take into consideration an adequate useful thickness for the installation of Natural Stone.

Paving in cubes and in pebbles require:

  • a useful thickness for installation equal to 10 cm for the 4/6 cm type
  • a useful thickness for installation equal to 12 cm for the 6/8 cm type
  • a useful thickness for installation equal to 14 cm for the 8/10 cm type

Square slab or opus incertum paving need:

  • a useful thickness for installation equal to 6 cm for stones with thickness between 1 and 3 cm
  • a useful thickness for installation equal to 8 cm for stones with thickness between 3 and 5 cm
  • a useful thickness for installation equal to 10 cm for stones with thickness between 5 and 7 cm
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