Base Layer CL 1 XX "Anthracite"

Apparent density is the ratio of mass to total volume, including all pores and voids. It differs from true density, which refers only to the solid substance itself and excludes voids. For comparison, water at 4 °C has a density of 1,000 kg/m³. Recycled tyre rubber granules (ELT), consisting mainly of SBR and natural rubber, have a true density of around 1,200 kg/m³. EPDM rubber granules have a true density of around 1,600 kg/m³.

For a moulded component made from rubber granules bonded with polyurethane, apparent density is calculated from its mass and external dimensions: length, width and overall height. This volume includes two types of void. The first consists of pores between the granules that remain after pressing during manufacture. Their proportion depends on moulding pressure, granule size, granule shape and the proportion of binder. As a simplified example, a uniformly compacted tile with a flat underside and an apparent density of 800 kg/m³ has a pore volume of around one third, assuming a granule true density of 1,200 kg/m³ and disregarding the binder proportion.

The second type consists of moulded voids created by a structured underside. Drainage channels, studs, drainage feet or pedestal feet leave open spaces beneath the wearing layer. These spaces form part of the overall height but contain no rubber granules. A moulded component with a pronounced underside profile can therefore have a low apparent density even where its wearing layer is densely pressed. Apparent density describes the complete moulded component, not the constituent substance alone. At WARCO, apparent density ranges from around 600 to 1,250 kg/m³.

The compaction of the wearing layer shapes the properties of the floor covering.

• Surface: the higher the density, the less open and more resistant the surface becomes.

• Water permeability: lower density means more open pores and, in most cases, greater water permeability.

• Elasticity: lower density makes the floor covering more yielding and elastic, while higher density makes it harder and stiffer.

• Weight: together with overall height, apparent density determines dry weight per square metre. When wet, water held in the pores adds to this weight. This matters for transport, installation and the load-bearing capacity of balconies, terraces and roof areas.

The scale runs from Rating 1 to Rating 5. Each rating represents a density range, for example Rating 2 for 780 to 840 kg/m³. For moulded components with a structured underside, the rating says less about the wearing layer than it does for a tile with a flat underside.

Rubber is an elastomer. Under load, it deforms and, once the load is removed, its cross-linked molecular chains draw it back largely to its original shape. In floor coverings made from rubber granules bonded with polyurethane, the porous structure adds a further mechanism. Pores remain between the rubber granules, while the elastic binder holds them together. Under load, it is mainly these pores that close, while the granules and binder deform at the same time. As deformation increases, the floor covering generally becomes stiffer and its resistance to further deformation increases. Elasticity and internal friction determine how it absorbs impacts, vibrations and footstep sound.

Shock absorption: when a body strikes the floor covering, its kinetic energy is absorbed over the deformation distance. One part is stored elastically and returned as rebound, while another is converted into heat through internal friction. The longer the deceleration distance, the lower the forces acting on the body and substrate. Under light loads, the floor covering yields only slightly. Only severe impacts make substantial use of the available deflection. A greater thickness of floor covering extends this distance. For safety tiles, the effect is assessed as critical fall height in accordance with BS EN 1177.

Vibration damping: rubber is viscoelastic, combining spring-like and viscous behaviour. Under cyclic loading from weights being set down, equipment in operation or machinery, deformation follows the applied force with a delay. The work done in this process is dissipated as heat through internal friction. The floor covering therefore acts as both a spring and a damper. Above the natural frequency of the system formed by the mass and floor covering, it decouples the vibration source from the substrate and reduces transmitted vibrations and shocks. The amount transmitted depends on the excitation frequency, the moving mass and the dynamic stiffness of the floor covering.

Footstep sound reduction: footstep sound is structure-borne sound. Walking, jumping or setting down objects introduces an impact into the substrate. It travels through the floor or ceiling structure and walls and may be heard as noise in other rooms. An elastic floor covering introduces a compliant layer into this transmission path. The peak force is spread over a longer period and is therefore lower, while part of the energy is converted into heat within the floor covering. The amount of structure-borne sound entering the building depends on the dynamic stiffness and thickness of the floor covering, as well as on the substrate.

The damping provided by a rubber granule tile depends on its density and pore content, the granule size and shape, the proportion of polyurethane binder and its thickness. As a rule, a dense, fine-grained tile deforms less and provides lower damping, whereas a porous, coarser or thicker tile provides greater damping. The scale ranges from Rating 1, noticeable damping, to Rating 5, very high damping, and is based on comparative measurements of WARCO products. Whether a product is suitable for a particular application is best assessed on site using a sample tile.

Water permeability describes the quantity of water that enters a porous floor covering and passes through it. In floor coverings made from rubber granules bonded with polyurethane, water does not pass through the rubber itself, which is impermeable. It moves through the open, interconnected pores between the granules under gravity. The flow rate depends on the proportion of open pores, their size and whether they form continuous paths. Coarse granules and lower moulding pressure during manufacture create larger open channels. Fine granules and higher moulding pressure reduce the pore spaces and can result in a practically impermeable tile.

Water permeability is measured in accordance with BS EN 12616 as an infiltration rate. This is the quantity of water passing through the floor covering within one hour under defined test conditions, expressed in mm/h. A rate of 1 mm/h corresponds to 1 litre per square metre per hour. Even a heavy rain shower supplies only a fraction of the water volume that a floor covering with a high rating can pass through over the same period.

The scale ranges from Rating 1 to Rating 5. Rating 1 represents an infiltration rate of approximately 0 mm/h, so the floor covering is practically impermeable to water. Rating 5 represents approximately 1,000 mm/h, equivalent to around 1,000 litres per square metre per hour. Classification is based on tests of representative tiles, with the results interpolated for the relevant product.

The tile is only one part of the construction. At Ratings 3 to 5, rainwater can pass through the tiled covering provided that the laying course and sub-base can also receive and drain it. On an impermeable substrate, water accumulates beneath the tiles. The area then requires a slope leading the water towards drainage, for example a drainage channel or outlet. Floor coverings with Ratings 1 and 2 are intended only for indoor and covered areas.

Water permeability can decrease over time if pores become blocked by tracked-in sand, leaves and fine dust. In stable mats, inadequate cleaning can also block the pores. Cleaning with water helps keep the pore structure open.

Heat is transferred by three mechanisms: conduction through a material, convection in air or water, and radiation. For a floor covering, conduction is the principal mechanism. It is described by thermal conductivity, expressed in W/(m·K). This value defines the quantity of heat passing each second through one square metre of a material one metre thick when the temperature difference between its two sides is one kelvin. The lower the value, the less readily the material conducts heat and the greater its insulating effect.

Solid rubber has a thermal conductivity of approximately 0.13 to 0.18 W/(m·K). Still air, at approximately 0.026 W/(m·K), conducts heat considerably less readily. Tiles made from rubber granules bonded with polyurethane contain pores that retain air and therefore conduct less heat than solid rubber. In general, lower density and a greater pore volume result in lower thermal conductivity. Moisture in the pores increases it again. Depending on density and structure, WARCO values range from approximately 0.07 to 0.14 W/(m·K).

Overall insulation depends not only on thermal conductivity but also on thickness. Thermal resistance equals thickness divided by thermal conductivity, so a tile with twice the thickness provides twice the thermal resistance. A structured underside with drainage channels or studs can also retain a layer of air beneath the tile, which may further reduce heat flow towards the substrate. This applies while the air remains still and dry. The effect is lower at contact points and in channels through which air can circulate.

The scale ranges from 1 to 5. Rating 1 corresponds to approximately 0.14 W/(m·K), while Rating 5 corresponds to approximately 0.07 W/(m·K). The values are based on measurements of representative samples and interpolated for the relevant product. Insulating materials such as extruded polystyrene (XPS) or mineral wool achieve values of approximately 0.03 W/(m·K).