This invention is concerned with improvements in or relating to building products and is particularly, although not exclusively, concerned with the manufacture of concrete roof tiles.

Concrete roof tiles are in the main formed by the well known roller and slipper process in which tile pallets are fed seriatim beneath the mortar hopper of a tile making machine, whereat when the machine is in use, mortar is fed onto the pallets to form a continuous ribbon thereon. Downstream ofthe mortar hopper, a cutting mechanism of the tile making machine is operated to cut the ribbon of mortar to form discrete "green state" tiles on the individual pallets which "green state" tiles are thereafter cured by conventional means.

The upper surfaces of the tiles so formed are generated by the roller and slipper and may therefore be of any desired profile across the width of the tiles so formed. For example, the tiles may have a so-called "shingle" appearance, i.e. the look of wooden shakes or shingles which are used predominantly in the United States of America.

The under-surfaces of the tiles, on the other hand, are formed by the pallets, that is, the surfaces of the pallets are shaped with recesses and channels to form hanging nibs, strengthening ribs and downwardly facing interlocking sidelock features of the tiles.

Conversely, in other tile manufacturing processes presently used, the tiles may be made upside down with, e.g. upper textured surfaces of the tiles being formed by appropriately shaped pallets and the under surfaces thereof being formed by the roller and slipper of the tile making machine.

Since the late 1970s, a considerable amount of time has been devoted to the development of multicoloured roof tiles having a "marbled" effect or a "rustic" appearance, that is a simulated weathered or stone-like appearance.

The "marbled" effect has been achieved by the partial mixing prior to extrusion of two or more coloured tile mortars, see WO 85/00135 of Marley Tile AG.

In the Specification of WO 85/00135 it is disclosed that the tile forming material may be supplied to the hopper by means of an elongate rotating screw conveyor in which mixing of colourants is effected, which colourants are introduced into the screw conveyor at appropriate positions along the length thereof and that the degree of mixing of each colourant, with the tile forming material in the hopper, is evident from the colour variations of the resultant roof tiles.

The "rustic" appearance has been achieved by the introduction of pigmented slurry, see GB 1577321 of Redland Roof Tiles Limited, or by the introduction of an acrylic paint or the like, see GB 2190891 A and GB 2186521 B of Anchor Building Products Limited.

In all three GB disclosures the colourant is introduced into the hopper of the tile making machine in such a way that the colourant appears as streaks of colour, e.g. black, on or in the surface of a tile of say, red, green or any other base colour.

The disclosure of WO 85/00135 of Marley Tile AG also relates to the combination of the two effects of marbling and creating a rustic effect by the mixing of two or more coloured mortars and by introducing one or more colourants into the partially mixed mortars to give an enhanced marble/rustic effect.

In each of the disclosures referred to the colourants, whether they are pigmented slurries or acrylic paints, are supplied through associated pipes or supply tubes respectively in GB 1577321 and WO 85/00135 while GB 2186521 B teaches the

introduction of acrylic paints into a tile hopper via the hollow spindle of a stirring paddle.

Irrespective of how the pigmented slurries or acrylic paints are introduced into their respective hoppers, there is provision in each of the disclosures referred to for switching the supplies on and off at regular and/or random intervals thereby obtaining extensive combinations of base or variable body colour and streaks on the upper surfaces of the tiles.

Invariably, where pigmented slurries or acrylic paints are fed to the screw mixer or the hopper of a tile machine, each colour is fed by a dedicated pump from a supply thereof through its own pipe or supply tube which is provided with its own on/off device for controlling the length and periodicity of the supply.

Obviously, such arrangements are costly to set up and maintain. It is, therefore, one of the aims of the present invention to provide an improved supply means for colourant which obviates the need for dedicated pumps and supply lines downstream of the pumps while providing in use, in a tile making machine, means for manufacturing concrete roof tiles of unsurpassed aesthetic appeal. The present invention thus provides a colourant feed means for supplying two or more colourants as herein defined to a mortar mixer for a building product comprising: a) two or more supplies of said colourants; and, b) control means downstream of said supplies of colourants for controlling, in random manner, the flow of each colourant or colourants from each supply thereof; characterised in that the colourant feed means also comprises a flow control device downstream of said control means for maintaining a flow of colourant to said mortar mixer commensurate with the amount of mortar in the mixer.

Preferably, the colourant feed means according to the preceding paragraph is charac¬ terised in that the control means comprises an on/off valve associated one each with each supply of colourant.

Conveniently, the colourant feed means according to the preceding paragraph is further characterised in that the control means further comprises time delay means associated one with each on/off valve to vary the speed at which each valve is switched to enable, in use, a gradual increase or a gradual decrease in the flow of a supply of colourant through each valve to the flow control device.

Preferably, the colourant feed means according to any one ofthe last three preceding paragraphs is further characterised in that a random signal generator is provided for enabling the control means to control in random manner, the flow of each colourant or colourants from each supply thereof.

The invention also provides a process for the manufacture of concrete roof tiles the colours of which mimic the natural colour variation of wood shakes said process comprising the steps of: a) feeding colourant from two or more supplies thereof to control valves associated one each with said supplies; b) effecting operation of said control valves independently one of the other and in a random manner to interrupt the flow of colour from each of the supplies thereof; c) feeding colourant or colourants from one or more of said supplies thereof to a common feed line downstream of said control valves; d) effecting the supply of the colourant or colourants through a common feed line to a mortar mixer, the flow rate of colourant or colourants through the common feed line being commensurate with the amount of mortar in the mortar mixer; e) admixing the colourant wholly or partially with tile mortar in said mortar mixer; f) forming "green state" tiles from said mortar; and, g) curing said "green state" tiles.

The invention further provides a concrete roofing tile manufactured by using the colourant feed means and process of the last five preceding paragraphs.

There now follows by way of example of the present invention a detailed description of the novel process and means for the production of roof tiles, which description is to be read with reference to the accompanying drawing.

In the manufacture of concrete roof tiles by conventional tile processing methods, it is usual to provide tiles with appropriate "marbled" and/or "rustic" colouring. This is especially so where such tiles are intended to give the appearance, in use, of cedar wood shakes or the like.

Such tiles 2 may be produced on a conventional tile machine 4 shown in the accom¬ panying drawing which tile machine 4 comprises a hopper 8 Iocated overlying a pallet conveyor 12. The conveyor 12 is of conventional design, is supported on floor mounted columns 12a and 12b and comprises support rails 12c on which pallets P are supported as they pass seriatim beneath the hopper 8.

The hopper 8 is also of conventional design and provides support for a roller 13, a slipper 14 and a pack shaft 16.

Located above the hopper 8 is a continuous mixer 18 for feeding mortar to the hopper.

Downstream of the hopper 8, the tile making machine is provided with a conventional tile cutting knife 20 which is mounted for reciprocal vertical and longitudinal movement on a knife carriage 22 illustrated schematically in the accompanying drawing.

The tile making machine also comprises a pallet spacing conveyor 24 which is arranged beneath the conveyor 12 and adjacent the knife carriage 22 for accelerating pallets P at the head of a series of such pallets away from the remaining pallets of the series.

When the machine is in use in the manufacture of concrete roofing tiles, a batch of mortar is fed by the mixer 18 to the hopper 8. At the same time, pallets P are fed seriatim along the support rails 12c of the conveyor 12 so that mortar in hopper 8 is compacted by the packshaft 16, to be thereafter formed, by the roller 13 and slipper 14, as a continuous ribbon of "green state" mortar on the pallets P.

The ribbon 26 of "green state" mortar is thereafter cut by the knife 20 ofthe tile cutting arrangement 22 whereupon the pallets P are engaged by the conveyor 24 whereby the "green state" tiles 2 on their associated pallets P are conveyed to racking devices prior to transportation to curing chambers.

In order to provide the tiles 2 with appropriate "marbled" and/or "rustic" colouring, the tile machine 4 is supplied with tile mortar from the continuous mixer 18 as aforesaid which mixer 18 is of conventional design having a screw augur 40 extending the length thereof as shown in the accompanying drawing.

A mixture of dry sand and cement is introduced to the mixer 18 at an upstream end 42 hereof via an inlet 44 with water being introduced via an inlet 46.

Upon rotation of the screw augur 40, the constituents of the mortar become admixed and are conveyed to a downstream end 48 ofthe mixer for discharge into the hopper 8 of the tile making machine.

Colourant, that is pigmented slurry, acrylic paint or the like, is normally introduced into the mixer via an inlet 50 at or towards the downstream end 48 of the mixer 18 to be mixed or partially admixed with the mortar mixture prior to being fed into the hopper 8.

Obviously, the degree of partial mixing of the colourant or colourants and the mortar mixture that is effected will be reflected in the colouring ofthe tiles produced thereafter in the tile machine 4.

The colourant introduced at the inlet 50 is supplied to the inlet 50 as aforesaid from a colourant feed means 51 via one or more of three colourant supplies 52, 54 and 56, indicated diagrammatically in the accompanying drawing.

From the above it will readily be appreciated that the tiles produced on the tile machine 4 using the novel colourant feed means 51 will be of many diverse shades and mixtures of colours depending upon the setting of on/off valves 62, 64 and 66 and a random signal generator 61.

In one example, a dark colourant from one supply is partially mixed with a light colourant from another supply and fed to the mixer 18 by a pump 72 at a rate commensurate with the supply of mortar mixture in the mixer. The effect obtained was that of even "marbling" of the upper surfaces of the tiles 4.

However, as the speed with which the valves associated with the supplies of dark and light colourants were switched on and off for varying periods of time under the control of the random signal generator, the dark colourant was emphasised at the expense of the light colourant to create a dark roof with lighter highlights or the situation may be reversed to give a light coloured roof with darker or dark patches.

Obviously, the combinations available with the novel feed means are limitless with the result that a most pleasing effect is obtained when the roof tiles 4 are laid on a roof.

The supplies 52, 54 and 56 are connected via associated on/off valves 62, 64 and 66 respectively which valves form part of a manifold 68 which, when the tile machine 4 is in use, directs one or more of the colourants via a common feed line 70 at a downstream end thereof, to a flow control device provided by a pump 72.

The pump 72 directs the colourant or colourants via a downstream pipe 74 into the inlet 50 of the mixer 18 as shown in the accompanying drawing.

ln the operation of the colourant feed means 51, the valves 62, 64 and 66 are operated in a random manner under the control of the random signal generator 61, whereby each of the valves is switched on or off for varying and, if required, overlapping time periods commensurate with supplying a volumetric amount of colourant or colourants to the downstream end ofthe manifold 68.

In addition, whereas the switching between one valve ofthe valves 62, 64 and 66 and a next to be operated of said valves or valves may be effected instantaneously, the valves 62, 64 and 66 may each be also caused to operate via an air bleed exhaust to enable, in use, a gradual increase or a gradual decrease in the flow of a supply of colourant through each valve 62, 64 and 66 to the pump 72.

Thus, the range of colour blends, available from the use ofthe process and colourant feed means provided by the present invention, is infinitely variable from a single light or dark colourant through all of the shades of these and any intermediately shaded colourants which are admixed therewith for varying periods of time as dictated by the random signal generator 61.

It will be also appreciated that the composite configuration of the colourant feed means provided by the invention obviate the need for separate supply lines and pumps which are evident in prior art arrangements.

In addition to a "marbling" of the tiles 2 produced by the process disclosed herein, additional colourant may be added to the hopper 8 via a pipe 9 to introduce streaks of colour into the upper surface in use of the tiles 2.