This invention relates to floor plates for use in the formation of raised flooring.

Raised flooring is widely used in modern building methods to provide flexibility in the location of. underfloor services such as cables and ducts, to simplify their installation and modification and to facilitate access to them.

In one widely used building method, such raised flooring is formed by assembling an array of floor plates on bearers such as posts or girders which space the plates above a sub-floor such as of the concrete shell of a building. The plates may be laid in such a way that they can easily be removed to expose the services located in the space below.

Natural materials, such as stone in particular, are widely favoured for flooring because they are hard wearing and readily cleanable and because of their aesthetic appearance. However, there is a problem in using such materials for raised flooring. This is because in the form in which such materials are generally most readily available for use in flooring, they comprise slabs which can be of uneven thickness and thus to get a level floor either the surfaces of the plates forming the floor have to be ground flat after assembly or else shims or other means have to be used between the plates and the bearers. Great accuracy is required in the levelling process as an unevenness of as little as 0-5 mm in the resulting floor can be unacceptable. Processes for manufacturing such slabs are therefore very expensive.

A second problem in using natural material in raised flooring is that the floor plates are only supported at the points at which they are in contact with the posts or girders. There is therefore a risk that cracking or even breaking of the plate may occur if a large or sudden force is applied in a region of the plate that is not directly supported

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particularly if there are any flaws or zones of weakness present in the natural material.

A further disadvantage of using stone is its density. At the thickness required to provide the desired load-bearing ability at economic bearer spacings, special ^' strengthening of the foundations of the building may be required to support the weight of the resultant floor.

EP 00530 2 describes a self-supporting floor slab comprising a slab of natural stone having a concrete layer bonded thereto via an adhesive. Any unevenness in the stone is compensated for by adjusting the thickness of the concrete layer. Such slabs, which are intended to be laid on the floor, would not be suitable for use in the raised flooring of the present invention as they would be liable to crack or break in the regions not supported by the posts or girders.

GB 56589*+ relates to a method of compensating for any unevenness in concrete slabs by providing the slab with shallow conςrete feet at each corner which are moulded to the slab before it has set.

These problems are overcome by the present invention which provides a composite flooring plate for use in raised flooring, said plate having a top face and an underface, said underface providing a plurality of load-bearing surfaces which are equidistant from the plane of the top face, and wherein the top face is provided by at least one slab or slice of natural material of uneven thickness, and said load-bearing surfaces are provided by at least one plastics moulding moulded against and bonded to substantially the total area of the back of said at least one slab or slice.

By means of the invention, any unevenness in the thickness of the slab or slice of natural material may be compensated in the moulding. Also, substantially thinner slabs or slices may be employed thereby

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significantly reducing the weight of the plates where the natural material has a density such as that of stone.

By appropriate choice of the moulding material, the plates may also be provided with other advantageous qualities such as sound deadening, thermal insulation and/or resilient compressibility.

While the following discussion of the invention relates to its application to floor plates having a surface of stone, it is to be understood that it may also be applied to other natural materials, e.g. wood. Also all references hereinafter to a "slab" also include a slice which may be wafer thin.

Previously, such wafer thin slices could not be used as they tended to crumble with wear. However, in the floor plates of the present invention, the moulding acts to reinforce the wafer and its integity is maintained even on extended wear.

Any suitable moulding material may be employed to form the moulding, including conventional building materials s,uch as concrete. However, in general a synthetic plastics material will be preferred, especially where the overall weight of the finished plate is a problem. Examples of suitable materials are thermoplastics such as polyolefins, polyamides, polycarbonates, polystyrene, vinylchloride polymers, acrylics and the like, and thermosetting and cold curing resins such as polyester, epoxy and phenolics. The moulding may be foamed or unfoamed and may contain fillers, e.g. for reinforcement and/or to reduce cost. Examples of suitable fillers are reinforcing fibres such as glass fibre and finely powdered solid fillers such as talc, fly ash, gypsum, silica, clay minerals and the like.

The moulding may also comprise two or more different materials, e.g. provided as layers one of which may be, for example, foamed and another, for example, unfoamed.

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It will be appreciated that it is not essential for the whole of the underface of the plate to be flat provided that the load-bearing surfaces are equidistant from the plane of the top face of the plate. For example, the underface may be dimpled or may be concave between the load-bearing surfaces, e.g. to increase the load-bearing properties of the plate and/or reduce its mass.

If desired, the load-bearing capacity of the load-bearing surfaces may be improved e.g. by forming the load-bearing surface of the different material to that of the moulding, e.g. metal. For example, metal plates may be attached to the load-bearing surfaces after moulding or may be provided as an integral part of the moulding.

The top face of each floor plate may comprise a single slab of stone or a plurality of slabs which may be firmly held in place in relation to each other by means of the moulded material.

In one method of forming the floor plates of the invention, the slab or slabs of natural material employed to provide, the top face of the plate may be located in the mouth of a mould of substantially regular, e.g. rectangular parallelopied shape, with the face(s) of the slab(s) intended to form the top surface of the plate facing outwards. Mouldable material may then be injected into the cavity behind said slab or slabs and caused to set against the back surface(s) of the slab or slabs to form the desired plate.

This method is particularly suitable for use with thermosetting or cold curing resins and some foam-forming mixtures. The moulds may be of simple construction from cheap and readily available materials, e.g. wood.

In an alternative method, the slab or slabs may be located in a suitably shaped closed mould with the face(s) of the slab(s) intended to provide the top surface of the plate facing outwards against one surface of the mould. A suitable mould-forming material is then injected into the cavity behind the slab or slabs.

This method is particularly applicable where the moulding is to be formed from an injection mouldable material such as a molten thermoplastic.

Some of the moulding materials may form a sufficiently strong bond with the natural material that a bonding agent is not required. In other cases, however, it may be desirable to treat those surfaces of the slab or slabs against which the moulding is to be formed, in order to improve the bond; e.g. by roughening the surface and or coating with a bonding agent. Another alternative would be to form in the surfaces re-entrant grooves into which the mouldable material is forced prior to setting.

The invention will now be illustrated with reference to the accompanying drawings in which:-

FIGURE 1 is one form of a flooring plate according to the invention with a flat underface; FIGURE 2 is an alternative form with a concave underface; FIGURE 3 is yet another alternative in which the load-bearing surfaces are reinforced; and FIGURE 4 shows a section of floor formed using the floor plates of the invention;

Referring to Figure 1, the flooring plate 2 has a top face 4 and an underface 6 providing load-bearing surfaces 8. The top surface is provided by a slab of natural stone 10 e.g. of granite or marble, and the load-bearing surfaces are provided by a moulding 12 which has been moulded against the back of the slab 10.

In Figure 2, where the reference numerals common with Figure 1 refer to the same features, the undersurface of the plate is concave between the load-bearing surfaces. It will be appreciated that a large or sudden force applied to the central region of the face of the flooring plate will be dissipated through the undersurface to the load-bearing surfaces.

In Figure 3. where the numerals common with Figure 1 relate to the same features, the load-bearing surfaces 8 are reinforced by means of metal plates 14 which are bonded to the moulded material 12.

In practice, an array of the flooring plates of the invention are supported on bearers such as posts or girders by meang of their load-bearing surfaces, e.g. as illustrated in Figure 4.

It can therefore be seen that the floor plates of the present invention have the following advantages over known floor plates:

(a) flat floors can be made from materials of uneven thickness;

(b) slabs may be thinner than would otherwise be required to span the distances between the support pests and girders;

(c) flawed materials which would otherwise be unsuitable because of their lack of load-bearing facility can be used;

(d) each floor plate can be made of a plurality of slabs which are held together by the moulding;

(e) the moulding supports the slab over substantially the whole of its back thereby reducing the liklihood of the slab cracking or breaking;

(f) the moulding may be resiliently compressible and therefore will act as a shock absorber;

(g) the moulding will deaden the sound of persons walking on the floor; and

(h) the manufacturing costs are reduced.