Patent Publication Number: US-2015084234-A1

Title: Building block and cladding system

Description:
The present invention relates to a building block, in particular, but not exclusively, the present invention relates to a building block that is suitable for cladding a wall and a corresponding cladding system, as well as to a method for manufacturing a building block and a method for cladding a wall. 
     Cladding of walls is a well-known technique used in the construction industry wherever it is desirable to cover art inner wall with a skin, or layer for decorative or functional reasons. 
     For example, to minimise construction costs, it is often desirable to construct an inner wall of a building from a relatively inexpensive material such as breeze blocks or cinder blocks. Such materials provide good structural support to the building but are often aesthetically unattractive. The inner wall may be vulnerable to weather damage or water ingress, for example if the material of the inner wall is porous or susceptible to damp. 
     In such circumstances, a cladding system can be used to cover the inner wall. Typically, such cladding systems comprise a plurality of brackets or rails that are affixed to the inner wall. Sheets or panels of a lightweight cladding material are attached to the rails, so as to create an outer skin that covers the inner wall. The cladding material can be attractive in appearance and can be resistant to water. Cladding materials currently in use include ceramic tiles, reconstituted stone boards, laminates, aluminium and fibre-cement board. 
     In some cladding systems, known as rainscreen cladding systems, the outer skin is arranged so that a cavity exists behind the cladding material. In such a case, the panels of cladding material deflect most of the water and wind striking the wall in bad weather. Water that penetrates the outer skin, through, the joints between the panels, enters the cavity and either drains away down the back face of the cladding or evaporates from the cavity. Any condensation that forms in the cavity is discharged in the same manner. In this way, the inner wall remains substantially dry, even though the outer skin may not itself be entirely watertight. 
     Cladding systems often incorporate one or more layers of thermally-insulting material between the cladding material and the inner wall. The thermally-insulating material serves to increase the thermal resistance, of R-value, of the clad wall, thus reducing heat loss from the building through the wall. 
     In addition to their use in the construction of new buildings, cladding systems can also be used to provide an outer skin over the walls of an existing building, for example to rejuvenate or change the appearance of the building, to improve its thermal insulation and weather resistance, and/or to protect the original building from weather damage. 
     Existing cladding systems tend to be relatively complex, expensive and difficult to install For instance, the brackets or rails must be adjustable to allow the panels to be properly aligned. The thermally-insulating material is usually added in a separate step, increasing the assembly time required. 
     Furthermore, it is normally desirable to connect the cladding panels to the brackets in such a way that no part of the connection is visible from she outside of the building. Such ‘secret fixing’ can make a cladding system even more complex to install and can mean that replacement of a single panel during maintenance work can require the removal and replacement of several adjacent panels. 
     Due to the complexity of existing cladding systems, the weather resistance and thermal insulation properties of the systems are often compromised. 
     Against this background, it would be desirable to provide a cladding system which is simple to construct and inexpensive to produce whilst also providing improved weather resistance and thermal insulation, and a building block suitable for use in such a cladding system. 
     Accordingly, in a first aspect, the present invention provides a cladding system for cladding a supporting wall, the cladding system including a plurality of building blocks, each having a body and a facing; and a plurality of support brackets for mounting the blocks on the supporting wall in a plurality of adjoining horizontal rows. The body of each block includes engagement means for engaging at least one of the support brackets such that, in use, at least a part of the body of each block abuts at least a part of the body of a neighbouring block in an adjoining row so as to guard against water penetration between the rows. 
     Because the bodies of blocks in adjoining horizontal rows abut one another, at least in part, the bodies of the blocks in the cladding system of the present invention provide a substantially continuous thermally insulating and water-proof barrier between the facings and the supporting wall. Unlike existing rainscreen cladding systems which typically have gaps between the cladding elements, in the present invention, the cladding system is substantially waterproof. 
     In one embodiment of the invention, in use, the weight of the blocks is supported by the supporting wall without the facings of adjacent blocks being in load-transferring contact. Because no significant load is transferred through the facings of the blocks in this arrangement, the facings of the blocks need not be designed to support the weight of the facings of other blocks. Consequently, the facings of the blocks can be significantly lighter than would otherwise be the case. Additionally, the support brackets need be designed only to support the weight of relatively low blocks. Thus the cladding system can be relatively low-cost and simple to make and install. 
     Optionally, to ensure that the facings of adjacent blocks are not in load-transferring contact, the facing of each block may he slightly smaller in area than a front face of the body of the block on which the facing is mounted. 
     Conveniently, the engagement means comprises bracket-receiving recesses in top and bottom faces of the body of each block for receiving respective upwardly-projecting and downwardly-projecting elements of the support bracket which project from a base member of the support bracket. 
     The engagement means may further comprise at least one cutaway in the body adjacent to at least one of the bracket-receiving recesses for receiving the base member of the support bracket. The or each cutaway may extend across a portion of the respective top or bottom face of the body, such that a remaining portion of the face can abut at least a part of a block in an adjacent row. In this way, the support brackets can be accommodated between blocks in adjacent rows without interrupting the body-to-body contact of the blocks. 
     In one embodiment, the base member of the support bracket is received in part in a cutaway in the top face of the body of a block, and in part in a cutaway in the bottom face of the body of a neighbouring block in an adjoining row. In this embodiment, the top and bottom faces of the block bodies can be identical so that the block can be installed either way up. 
     The support bracket and the blocks are preferably dimensioned such that, in use, a cavity is provided between the wall and the blocks. Such a cavity advantageously improves the insulating properties of the cladding system, and also provides an air gap into which any water that penetrates between the blocks can pass, whereupon the wafer can evaporate or drain away. 
     In one-embodiment, the facing of each block is of a first material, and the body of each block is of a second material, the second material having a lower density than the first material. The body of each block is preferably of a lightweight material, which is optionally thermally insulating also. In this way, the blocks are easier and safer to handle manually than would otherwise be the case. The body may for example be of expanded polystyrene. The facing of each block may be a cementitious material. 
     In use, at least a part of the body of each block may abut at least a part of the body of a neighbouring block in the same row, so as to guard against water penetration between the blocks within a row. Accordingly, in this arrangement, the body of each block abuts its neighbours on all four sides, so as to form a substantially continuous thermally insulating layer parallel to the supporting wall. The layer is also substantially waterproof. 
     In one embodiment, the facing of each block includes an overhanging portion that extends beyond the body of the block, such that, in use, the overhanging portion of the facing overlaps the facing of a neighbouring block in an adjoining row. Preferably, the overhanging portion of the facing extends beyond a bottom surface of the body and, in use, overlaps a top portion of the facing of a neighbouring block in the row below, in such an arrangement, the cladding system gives the appearance of, for example, wood shake siding. 
     In a second aspect, the present invention provides a body for a building block, the body being shaped to engage with the material of a facing in such a manner as to guard against relative movement of the facing with respect to the body in any direction. 
     By virtue of the shape of the body, the facing of a building block which includes such a body is resistant to slip or creep with respect to the body. For example, the facing unlikely to slide downwards under the force of gravity when the building block is installed with the facing in a vertical orientation, such as in a wall. Similarly, the facing is resistant to lateral movement, and to being pulled away from the body. Thus such a building block is mechanically stable, and is suitable for use in a cladding system. 
     Furthermore, since the body can hold a facing in a particularly secure engagement with the body, a building block consisting of such a body with a facing attached thereto can be transported, handled and used as though it were a unitary component, even when the material of the body is different from the material of the facing. 
     The body and the facing materials can be different types of materials, and the materials used can be chosen so as to optimise the performance of a building block including the body of the second aspect of the invention. For example, because the body is shaped to engage with a facing material, the appearance and weather-resistance of the material of the body may not be important, since those properties can be bestowed on a building block by appropriate selection of a facing material. 
     In a particularly advantageous embodiment of the invention, the body is of a lightweight, thermally-insulating material such as expanded polystyrene. The use of such a material gives the body a high thermal resistance or R-value, making it suitable for use in many applications where thermal insulation is important. Furthermore, since the material is lightweight, building blocks including such bodies can be made light enough for repeated handling by an individual, whilst being of a reasonable size to allow rapid construction using the blocks. 
     The engagement of the body with the facing preferably incorporates engagement surfaces of the body which engage with complementary engagement surfaces of the facing, in this way, the engagement surfaces of the body provide a secure and movement-free engagement with the facing. 
     It is particularly advantageous if the engagement surfaces of the body are oriented with respect to a front face of the body in such a manner as to form an interlock with the engagement surfaces of the facing in order to guard against relative movement of the facing with respect to the body in three mutually perpendicular directions. 
     In this case, an interlock between the body and the facing material arises by virtue of the orientation of the engagement surfaces of the body. Because the effect of the interlock is to guard against relative movement of the facing with respect to the body in three mutually perpendicular directions, movement of the facing with respect to the body in any direction is substantially prevented in normal use. 
     In one embodiment the engagement surfaces of the body define walls of a recess in the from face of the body. Preferably, at least one of the side walls is inclined to define an undercut region of the recess. Advantageously, when the engagement surfaces of the projection engage with the undercut region, movement of the facing with respect to the body in a direction normal to the front face of the body can be guarded against. Thus the undercut region helps to stop the facing being displaced outwardly from the body. 
     The recess may incorporate two opposing side walls which diverge in a direction away from the front face of the body. The recess may, for example, incorporate a dovetail mortise. The opposing side walls help to stop the facing being displaced laterally with respect to the body. 
     The recess may extend linearly across a part of, or the whole of, the front face of the body. Said another way, the recess may extend linearly across the front face of the body from one edge of the front face to another, preferably opposite, edge of the front face, or the recesses may stop short of the edges of the front face. In one example, the recesses extend between opposite edges of the front face of the body across the shortest dimension of the front face. In one method of manufacturing of a building block incorporating a body according to the second aspect of the invention, in which a facing material is cast onto the front face of the body, the provision of such linearly-extending recesses in the body helps to ensure that the facing material fills the recesses. 
     The recess, may incorporate one or mom arcuate wall portions. For example, in one embodiment, the recess incorporates at least two oppositely-facing arcuate wall portions. 
     Preferably, the recess incorporates a linear portion which extends in a first direction, and wherein the or each arcuate wall portion curves outwardly from the linear portion in a second, perpendicular direction. In a building block incorporating such a body, the linear portion of the recess helps to guard against displacement of the facing with respect to the body in a first direction lying parallel to the front face of the body, while the arcuate wall portions help to guard against displacement of the facing with respect to the body in a second direction lying parallel to the front face of the body and being perpendicular to the first direction. 
     Preferably, there is a plurality of recesses, each recess being of one of the types described above. All of the recesses of the plurality may be of the same shape, or a plurality of different shapes of recess may be provided. When a plurality of recesses are provided, the engagement surfaces can be spread over a greater area of the body, and therefore the body can engage a facing more securely, than if only one recess were provided. 
     The body may conveniently be capable of acting as a mould for the facing. In this case, the shape of the body serves as a mould frame or template for the shape of the facing, such that the facing is complementary in shape to the body. In this way, the facing can be permanently attached to the body to form a building block in a straightforward manufacturing process. 
     The body may incorporate a plurality of drainage channels in a rear face of the body. For example, a plurality of drainage channels may be provided which are arranged to extend downwardly in use. The body may include one or more inclined channels or slots in the top face of the body for directing water towards the rear face of the body. The inclined channels may define a gutter in a top face of the body to direct wafer into the drainage channels, when present, in use. When a plurality of building blocks incorporating such bodies are assembled together to form a wall-like structure, such drainage channels, and gutters if present, advantageously allow any water that penetrates the structure to drain down the rear surface of the bodies. This is particularly useful when the structure, is a cladding for an internal wall since by these means the penetrating water is directed away from the internal wall. 
     in a third aspect, the invention extends to a building block having a body according to the second aspect of the invention, and a facing which engages with the body in such a manner as to guard against relative movement of the facing with respect to the body in any direction. 
     In a particularly preferred embodiment of the third aspect of the invention, the facing is of a cementitious material For example, the facing could be formed from a cement, sand and water mixture, a concrete mixture comprising cement, sand, aggregate and water, or a reconstituted stone material. A facing of cementitious material can be relatively low-cost, and offers a high degree of resistance to environmental factors such as water, pollution, wind erosion and so on. Furthermore, such a facing can readily be given an attractive appearance, For example, the facing could be moulded so as to have a textured or patterned face to mimic a natural material such as stone or wood, or could be polished, glazed or otherwise finished. Similarly, the material of the facing could be coloured or dyed or, since many cementitious materials accept paint readily, the facing could be painted or otherwise coated. 
     The facing preferably includes engagement surfaces which interlock with engagement surfaces of the body. The engagement surfaces of the facing may, for example, define a projection which extends from a rear face of the facing and interlocks with a corresponding recess in a front face of the body. The projection optionally incorporates a dovetail tenon, which conveniently interlocks with a dovetail mitre in the front face of the body. Alternatively, or in addition, the projection may incorporate one or more arcuate wall portions which interlock with one or more corresponding arcuate wall portions of a recess in a front face of the body. Advantageously, the facing and the projection are integral For example, when the facing material is cast onto a front face of the body during manufacture of the block, the projection may be formed by filling a corresponding recess in the front face of the body with the facing material. 
     Vertical and/or horizontal grooves may be provided in the facing to give the visual impression that each block includes a plurality of smaller blocks, in one embodiment, in which the facing includes projections for engagement with recesses in the body, vertical grooves are provided in the facing at irregular intervals across the width direction of the facing, to mimic the appearance of natural elements having a plurality of different widths. Advantageously, each vertical groove in the front face of the facing coincides with the position of a projection on the rear face of the facing, in this way, each groove is located where the thickness of the facing is at its greatest, so as to guard against the risk of mechanical failure. 
     In a fourth aspect of the invention, a method of manufacturing a building block having a body arid a facing is provided. The method includes casting a settable facing material onto the body of the to form the facing which engages with the body during casting in such a manner as to guard against relative movement of the facing with respect to the body in any direction when the facing material has set. 
     By virtue of this method, a building block having a body which is securely engaged with a facing can be easily and conveniently manufactured using a pre-formed body. It is not necessary to pro-form a separate facing, since the facing of the block is both shaped and attached to the body in the same operation. 
     To this end, engagement surfaces on the facing may be formed during casting of the facing to interlock with engagement surfaces of the body. 
     Preferably, the settable facing material is a cementitious material. Alternatively, the settable facing material may be a curable resin, a melt or a similar material. The facing material may be pourable or, as for example in the case of a relatively dry cementitious mix, the facing material may be non-pourable. 
     The method of the fourth aspect of the invention can be used to manufacture a building block according to the third aspect of the invention. 
     In a fifth aspect of the invention, a body for a building block is provided which has a first groove in a face thereof and a second groove in an opposite face thereof arranged so that, when a plurality of such blocks are assembled together to form a wall, the first groove cooperates with the second groove of a neighbouring block to define a cavity for a deformable, sealing material, wherein the first groove includes a ridge which projects inwardly into the cavity to facilitate deformation of the sealing material within the grooves when the blocks are assembled together with the sealing material therebetween. 
     In this way, when the blocks are assembled together, the ridge helps the sealing material to form a seal between the blocks by pressing the sealing material against the walls of the grooves. The seal is particularly useful in guarding against the penetration of air through the assembly between neighbouring blocks. 
     To facilitate deformation of the sealing material, the first groove may be W-shaped in cross-section, the ridge being the peak of the ‘W’. Similarly, the second groove may be ‘V’-shaped or ‘U’-shaped in cross-section. The grooves may for example be provided in oppositely-disposed top and bottom faces of the body, or in oppositely-disposed side faces of the body, although in a preferred embodiment the grooves are provided in oppositely-disposed top and bottom faces of the body and in oppositely-disposed side faces of the body, in that case, each, groove may extend over a respective corner of the body. 
     The body of the fifth aspect of the invention may incorporate features of the first to third aspects of the invention also. A building block incorporating the body of the fifth aspect of the invention may be manufactured by the method of the fourth aspect of the invention. 
     In a sixth aspect of the present invention, a body for a building block for use in the cladding system of the first aspect of the invention is provided, in which top and bottom faces of the body include bracket-receiving recesses for receiving respective upwardly-projecting and downwardly-projecting elements of the support brackets which project from a base member of each support bracket. By virtue of this arrangement, building blocks incorporating such bodies are self-aligning when they are mounted on the support brackets. 
     The bracket-receiving recesses are advantageously in the form of channels extending across the width of the body to allow the block to slide laterally on the support brackets when mounting the building blocks on the supporting wall. Thus, during assembly of the cladding system, the blocks can be slid along the support brackets. 
     The body preferably comprises at least one cutaway in the body adjacent to at least one bracket-receiving recess to accept the base member of the support bracket. By virtue of the cutaway, the bodies of adjacent blocks can be placed into abutting contact during assembly of the blocks in a cladding system, which helps to prevent wind-driven water and air from passing between the blocks. 
     As in other aspects of the invention, the body may comprise a plurality of drainage channels in a rear face of the body, and optionally a gutter in the top face of the body to direct water into the drainage channels, in use. 
     The body may include a removable portion of the body arranged to support an overhanging portion of a facing during manufacture of a building block using the body. 
     The body of the sixth aspect of the invention may also include features of, or be in accordance with, the second and/or the fifth aspect of the invention. Alternatively, or in addition, the body of the sixth aspect of the invention may be incorporated in a building block having features of, or being in accordance with, the building block of the third aspect of the invention. 
     In a seventh aspect, the present invention extends to a support, bracket for use in the cladding system of the first aspect of the invention. The support bracket comprises mounting means for mounting the bracket on the supporting wall; and support means to engage with the blocks. 
     The mounting means may comprise an upstanding member of the bracket, which may for example include holes through which fasteners such as nails or screws can be inserted, in this way, the support bracket can easily be mounted to a supporting wall. 
     The support means of the support bracket preferably comprises a plurality of upwardly-projecting and downwardly-projecting elements which project from a base member of the support bracket. This arrangement aids alignment of the blocks of the cladding system, since the upwardly-projecting elements engage with a first block on one side of the support, bracket while the downwardly-projecting elements engage with a second block on the other side of the support bracket. The first and second blocks are thereby aligned with one another. The upwardly-projecting elements may be interdigitated with the downwardly-projecting elements. 
     The support bracket may include drainage means for allowing fluid such as air or water to pass through the support bracket. Thus, when the support bracket is installed in a cavity, the drainage means allow wafer to drain within the cavity, furthermore, the drainage means allows air to move within the cavity, which aids evaporative dispersion of water from the cavity. The drainage means may, for example, include holes or silts. 
     In an eighth aspect of the present invention, a method of cladding a supporting wall is provided. The method includes mounting a support bracket to the wall, placing a first building block on the support bracket, placing a second building block on the support bracket, and sliding the second block into abutment with the first block. This method is a particularly straightforward way of assembling blocks to clad a wall, since it avoids the need to use fasteners, clips and so on, and allows neighbouring blocks to be easily abutted and aligned. 
     The method preferably includes forming a seal between the first and second blocks. For example, the method may include placing a sealing material between the first and second blocks before sliding the second block into abutment with the first block so as to form a seal between the blocks. 
     The method may also extend to cladding a corner between first and second adjacent supporting walls, in which case the method includes mounting a support bracket to each wall, removing a portion of the body of the first building block to leave an overhanging portion of the facing, placing the first block on the support bracket mounted to the first wall, so that the overhanging portion of the facing projects beyond the corner, placing the second block on the support bracket mounted to the second wall, and sliding the second block into abutment, with the first block, so that a side face of the body of the second block abuts a rear face of the overhanging portion of the facing of the first block. It will be appreciated that the order in which the blocks are placed on the wall is interchangeable. 
     Since this expression of the method includes removing a portion of the body of a building block, blocks that are specially designed for fitment at corners, sometimes known in the ad as ‘specials’, need not be provided, instead, the building blocks provided can ail be identical in form and, when a corner is encountered when performing, the method, blocks can be modified as appropriate by removing the necessary portion of the body of each block. Accordingly, it is preferred that the body of each block is of a cuttable material, such as expanded polystyrene referred to previously. 
     The method of the eighth aspect of the invention is preferably used for cladding a wall with the cladding system of the first aspect of the invention. 
    
    
     
       Preferred embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which: 
         FIG. 1  is a perspective view, from the front, of a building block according to one embodiment of the present invention: 
         FIG. 2  is a perspective view, from the rear, of the building block of  FIG. 1 ; 
         FIG. 3  is a top view of the building block of  FIG. 1 ; 
         FIG. 4  is a side view of the building block of  FIG. 1 ; 
         FIG. 5  is a perspective view, from the rear, of the facing of the building block of  FIG. 1 , in isolation from the body of the building block; 
         FIG. 6  is a perspective view, from the front, of the body of the building block of  FIG. 1 , in isolation from the facing of the building block; 
         FIG. 7  is an exploded top view of the building block of  FIG. 1 ; 
         FIG. 8  shows, schematically and in perspective view, a sequence of steps in the manufacture of a plurality of building blocks of the type shown in  FIGS. 1 to 4 ; 
         FIG. 9  shows, in part-sectional side view, some of the steps in the manufacturing process of  FIG. 8 ; 
         FIG. 10  is a top view of a mould frame used in the manufacturing process of  FIG. 8 ; 
         FIG. 11  is a cross-sectional side view of the mould frame of  FIG. 10 ; 
         FIG. 12  is a cross-sectional side view of a mould shoe used in the manufacturing process of  FIG. 8 ; 
         FIG. 13  is a perspective view of a wall that has been partially clad using a cladding system comprising a plurality of building blocks of the type shown in  FIGS. 1 to 4 , and a plurality of support brackets; 
         FIG. 14  is a perspective view of the partially clad wall of  FIG. 13  showing, in greater detail the building blocks and the support brackets; 
         FIG. 15  is a perspective view of the partially clad wall of  FIG. 13  showing, in greater detail, the building blocks, the support brackets, and a bottom support bracket; 
         FIG. 18  is a side view of the partially clad wall of  FIG. 13 ; 
         FIG. 19  is a vertical cross-sectional view showing part of two vertically neighbouring building blocks in the cladding system of  FIG. 13 ; 
         FIG. 18  is a plan view showing a corner in a wall clad with the cladding system of  FIG. 13 ; 
         FIG. 19  is an exploded drawing in plan view of two building blocks arranged to form the corner shown in  FIG. 18 ; 
         FIG. 20  is a perspective view, from the front, of a variant of a building block according to the present invention, having a decorative appearance; 
         FIG. 21  is a perspective view, from the front, of a building block according to another embodiment of the present invention; 
         FIG. 22  is a perspective view, from the rear, of the building block of  FIG. 21 , 
         FIG. 23  is a top view of the building block of  FIG. 22 ; 
         FIG. 24  is a side view of the building block of  FIG. 21 ; 
         FIG. 25  is a side view of a block of the type shown in  FIGS. 21 to 24  in use in a cladding system, and a plurality of support brackets; 
         FIG. 28  is a perspective view, from the front, of a variant of the building block of  FIG. 21 ; 
         FIG. 27  is a perspective view, from the rear, of the building block of  FIG. 26 ; 
         FIG. 28  is a top view of the building block of  FIG. 28 ; 
         FIG. 29  is a side view of a building block according to another embodiment of the invention; 
         FIG. 30  is a side view of a wall that has been partially clad using a cladding system comprising a plurality of building blocks of the type shown in  FIG. 29 , and a plurality of support brackets; 
         FIG. 31  is a top view of the building block of  FIG. 29 ; 
         FIG. 32  is a perspective view of the partially clad wall of  FIG. 30 ; 
         FIG. 33  shows, schematically and in perspective view, a sequence of steps in the manufacture of a plurality of building blocks of the type shown in  FIGS. 29 to 32 ; and 
         FIG. 34  is a side view of a building block of the type shown in  FIGS. 29 to 32  in an intermediate stage of manufacture. 
     
    
    
     Throughout this specification, terms such as “top” and “bottom”, “upper”, “lower” and “side”, “front” and “rear”, “horizontal” and “vertical” are used with reference to the orientation of the building blocks as they would be placed during normal use in a walling application, as shown in for example  FIG. 1 , although it will be appreciated that the blocks could be used in different orientations. 
       FIGS. 1 to 4  show a building block  20  according to the present invention. The building block  20  comprises a body  22  and a facing  24  attached thereto. The facing  24  is made from a cementitious material formed from a mixture of cement, sand and water, and optionally aggregate, and the body  22  is made from a low-density, thermally insulating material such as expanded polystyrene. 
     The facing  24  has a front face  28  surrounded by a chamfered edge  28  and a rear face  30 , which is innermost when the facing  24  is attached to the body  22 .  FIG. 5  shows the facing  24  in isolation from the body  22 , so that the rear face  30  of the facing can be seen in detail. Several projections  32  extend rearwardly from the rear face  30  of the facing  24 . 
     The facing  24  abuts a front face  34  of the body  22 , so that the front face  34  of the body  22  is innermost when the facing  24  is attached to the body  22 .  FIG. 8  shows the body  22  in isolation from the facing  24 , so that the front face  34  of the body  22  can be seen in detail. The front face  34  is provided with several recesses  38 , which interlock with the projections  32  of the facing  24 . 
     As shown most clearly in  FIG. 5 , each projection  32  extends vertically from the top to the bottom of the facing  24 . As shown additionally in  FIG. 7 , each projection  32  includes inclined side walls  38  which diverge outwardly to meet the rearmost surface  40  of each projection  32 . The side walls  38  on opposing sides of the projection  32  therefore undercut the rearmost surface  40  of the projection, so as to form a dovetail tenon. 
     At two positions along each projection  32 , at approximately one-third and two-thirds of the height of the facing  24 , the side walls  3 B on opposite sides of each projection  32  include arcuate portions  42 . Each pair of arcuate portions  42  can be considered to define a cylinder having an axis extending normal to the rear face  30  of the facing  24 . Thus each projection  32  has the shape of a bar with a trapezoidal cross section, extending linearly from the top to the bottom of the facing  24 , superimposed on the two cylinders defined by the arcuate wall portions  42 . 
     Referring in particular to  FIGS. 5 ,  6  and  7 , the projections  32  on the rear face  30  of the facing  24  have a complementary shape to the recesses  38  in the front face  84  of the body  22 . The recesses  36  are in the shape of channels which extend from the top to the bottom of the body. The opposing walls of the channels are generally inclined and diverge outwardly moving rearwardly from the front face  34  of the body  22 , thereby to form a dovetail mitre, having an overhanging lip  44  on both sides thereof. 
     Additionally, as shown in  FIG. 6 , each of the recesses  38  includes two pairs of oppositely-facing arcuate wall portions  46 . Each pair of arcuate wall portions  46  can be considered to define a cylindrical bore in the front face  34  of the body  22 , having a cylinder axis extending normal to the front face  34 . Thus each recess  36  incorporates a linear portion, in the form of a dovetail mitre, which extends vertically on the front face  34  of the body  22 , and arcuate wall portions  46  which curve outwardly from the linear portion in a horizontal direction. 
     The arcuate wall portions  46  of the recesses  36  accommodate the arcuate wall portions  42  of the protections  32 . Thus, in the building block  20 , the projections  32  and the recesses  36  interlock so as to hold the facing  24  securely on the body  22 . 
     As will now be described, the projections  32  and the corresponding recesses  36  are shaped so as to guard against relative movement of the facing  24  and the body  22  in any direction. 
     The overhanging lips  44  of the recesses  36  extend into the undercut regions of the projections  32 , so as to guard against movement of the facing  24  in a direction normal to the front face  26  of the facing  24 . Said another way, the dovetail tenons defined by the projections  32  cooperate with the dovetail mitres defined by the recesses  36  interlock to prevent the facing  24  being pulled away from the body  22 . 
     Furthermore, the inclined side walls  38  of the projections  32  abut the walls of the channels which form the recesses  36 , so as to guard against relative sideways, i.e. horizontal, movement of the facing  24  and the body  22 . 
     Finally, the arcuate wall portions  42  of the projections  32  engage with the corresponding arcuate wall portions  46  of the recesses  36 , preventing relative upward or downward, i.e. vertical, movement of the facing  24  with respect to the body  22 . Said another way, the interaction of the arcuate wall portions  42  of the projections  32  and the arcuate wall portions  48  of the recesses  36  prevents the facing  24  from slipping downwards on the body  22  under the force of gravity when the building block  20  is installed in the orientation shown in  FIG. 1 . 
     In general, therefore, the walls of the projections  32  and recesses  36  comprise engagement surfaces of the facing  24  and the body  22 , respectively. The engagement surfaces of the body  22  are oriented with respect to the front face  34  of the body  22  in such a manner as to form an interlock with the engagement surfaces of the facing  24 . The interlock thus formed guards against relative movement of the facing  24  with respect to the body  22  in three mutually perpendicular directions. In this embodiment, the three directions lie normal to the front face  34  of the body  22 , horizontally, and vertically, as described above, but it will be understood that orienting the engagement surfaces of the body  22  so as to prevent relative movement in any three mutually perpendicular directions will have the desired effect. 
     It is to be noted that this arrangement of recesses  36  and complementary projections  32  does not rely merely on an interference fit to engage the facing  24  with the body  22 . Instead, the body  22  is shaped to interlock with the facing  24  to guard against movement of the facing  24  with respect to the body  22  in every direction. Consequently, the facing  24  is held securely on the body  22 , and is not vulnerable to detachment due to vibrations, mechanical shock, differential thermal expansion of the body  22  and the facing  24  and so on. 
     As seen most clearly in  FIG. 2 , the body  22  of the building block  20  is provided with an array of vertically-extending drainage channels  50  on its rear face. The channels  50  allow water to drain down the back of the block  20  in use. The body  22  is also provided with a shallow V-shaped groove  52  in its top face, as shown in particular in  FIG. 4 . The groove  52  acts as a gutter to direct wafer from the top face of the block  20  toward the channels  50 . 
     An upper bracket-receiving channel or recess  54  is formed in the top face of the body  22 , and a lower bracket-receiving channel or recess  56  is formed in the bottom face of the body  22 . As will be described in more detail below, the upper and lower bracket-receiving recesses  54 ,  56  are arranged to cooperate with support brackets when the building block  20  is used in a cladding system. The body  22  is further provided with grooves  82 ,  84  on the top, bottom and side faces thereof for receiving a bead of sealing material, as will also be described further below. 
     A method of manufacturing building blocks will now be described with reference to  FIGS. 8 to 11 . The method is particularly suitable for manufacturing the building blocks described above with reference to  FIGS. 1 to 7 , but it will be appreciated that the method could also be used for manufacturing other types of building block having a body and a facing. 
       FIG. 8  shows a plurality of blocks  20  being made simultaneously, while  FIG. 9  shows the processing steps for one such block  20 . 
     As shown in  FIG. 8(   a ), the blocks are manufactured by building up the blocks as they are transported along a manufacturing line (not shown) on a pallet  80 . A plurality of block bodies  22  are arranged on the pallet  80 , as shown in  FIGS. 8(   b ) and  9 ( a ), so that the recesses  32  are uppermost. 
     A mould frame  82  is then placed around the bodies  22 , as shown in  FIGS. 8(   c ) and  9 ( b ). The mould frame  82  is shown in more detail in  FIGS. 10 and 11 . The mould frame  82  comprises a plurality of openings  84 , each configured to fit tightly around a respective body  22 , As shown most clearly in  FIGS. 9(   b ) and  11 , the mould frame  82  includes a flared region  86  at the bottom end of each opening  84 . The flared region  88  aids alignment of the mould frame  82  with each body  22 . 
     Once the mould frame  82  is in place, the facing  24  of the block is formed by pouring a settable material, such as a wet cementitious mixture which hardens on exposure to air, into the opening  84  to fill the gap between the front face  34  of each body  22  and the top of the mould frame  82 , as shown in  FIGS. 8(   d ) and  9 ( c ). The cementitious mixture is poured in such a way that the recesses  32  in the body  22  are completely filled by the cementitious mixture, for example by pouring the concrete in a direction perpendicular to the long axes of the recesses  32 , as indicated by arrow  88  in  FIG. 8(   d ). 
     Mould shoes  90 , one of which is illustrated in  FIG. 12 , are then pressed down onto the wet cementitious mixture, in each aperture  84  of the mould frame  82 , as shown in  FIG. 9(   d ). Each shoe  90  includes on its undersurface  92  a relief pattern, so that any desired decorative relief features or texture patterns are transferred to the surface of the facing  24  when the shoe  90  presses on the wet cementitious mixture. The shoe  90  also includes a chamfered lip  94  around the periphery of its undersurface  92 , which moulds the chamfered edge  28  of the facing  24  of each block  20 . 
     The cementitious mixture is compacted by the mould shoe  90  to ensure that the facing  24  is free from pores and other defects, and to ensure that the recesses  32  are filled by the facing material. 
     Once the cementitious mixture has set sufficiently, the mould frame  82  is removed from the pallet  80 . The finished blocks  20 , as shown in  FIGS. 8(   e ) and  9 ( e ), are then removed from the pallet  80  and stacked as shown in  FIG. 8(   f ) to allow the facings  24  to set fully. The stack of blocks  20  can he packaged for storage and transportation. 
     Although the body  22  and the facing  24  are shown separated from one another in  FIGS. 5 ,  8  and  7 , it will be appreciated that since the body  22  acts as a mould to form the projections  32  of the facing  24 , the facing  24  is permanently attached to the body  22  and is not removable. 
     Furthermore, since the body  22  acts as a mould for the facing  24 , the shape of the body alone gives rise to the engagement between the body  22  and the facing  24 , which guards against relative movement of the facing  24  with respect to the body  22  in any direction as described above. 
     The thickness of the facing  24  is determined by the size of the gap between the front face  34  of each body  22  and the top of the mould frame  82 , as shown in  FIGS. 9(   b ) and  9 ( c ). Optionally, the mould frame  82  comprises a stack of removable mould plates (not shown) so that, by adding or removing plates, the size of the gap, and hence the thickness of the facing  24  can be adjusted. 
     It will be appreciated that the arrangement of projections  32  and recesses  36  described above is only one example of a suitable arrangement. The recesses in the front face of the body could instead comprise separate dovetail mitres and cylindrical bores. Inclined, curved or ‘s’-shaped dovetail mitres, one or more rectangular recesses having undercut regions oh one or mere sides, an array of circular recesses having undercut sides and so on. The recesses could also take the form of an undercut groove which extends around the periphery of the front face of the block. 
     A cladding system utilising the blocks  20  will now be described with reference to  FIGS. 13 to 19 . 
     The cladding system, shown generally in  FIG. 13 , comprises a plurality of blocks  20  of the type shown in  FIG. 1 , which are supported on an inner wall  100  by a plurality of support brackets  102 . The inner wall  100  may be made from a conventional building material, such as brick, block, timber or masonry. 
     As shown most clearly in  FIG. 14 , each of the support brackets  102  comprises an upstanding mounting member  104  at the rear of the bracket, a horizontal base member  106  connected at its rear edge to the mounting member  104  to form an L-shaped section, and alternating upwardly-extending and downwardly-extending fingers or elements  108 ,  110  connected to the front edge of the base member  106 . Conveniently, the mounting member  104 , base member  106  and fingers  108 ,  110  are formed by cutting or stamping and then bending a piece of sheet material such as steel, so that each support bracket  102  is integrally formed. Alternatively, the support brackets  102  may be formed from a reinforced plastics material, for example by injection moulding or by another suitable manufacturing method. 
     As shown in  FIG. 15 , the cladding system also includes a base bracket  112  having an upstanding rear mounting member  114 , a horizontal base member  116  and an upstanding front wall  118  comprising a plurality of upwardly-extending fingers. The mounting member  114  and front wall  118  of the base bracket  112  are connected to rear and front edges of the base member  116  respectively, so that the base bracket  112  has a J-shaped cross section. The base bracket  112  may also be integrally formed from a sheet material. 
     The support brackets  102  and base bracket  112  include, strengthening ribs  120  to ensure that the brackets  102 ,  112  are sufficiently rigid to bear the weight of-the blocks  20 . The support brackets also include drainage holes or slits (not shown) to allow drainage of moisture in the space between the blocks  20  and the inner wall  100  and to allow air to circulate within that space. 
     To clad the inner wall  100 , the base bracket  112  is first fixed to the inner wall  100  by screwing, nailing or otherwise attaching its mounting member  114  to the inner wall  100 . A first row or course  122  of blocks  20  is then assembled on the base bracket  112  as will now be described. 
     A first block  20  is placed on the base bracket  112  so that the upstanding front wall  118  of the base bracket  112  locates in the lower recess  56  of the block  20 . A bead of sealing compound is then applied to one of the grooves  82 ,  84  in a side face of the block  20 . 
     A second block  20  is then placed on the base bracket  112 , leaving a horizontal gap between the first and second blocks  20 , The second block  20  is then slid horizontally along the base bracket  112 , so as to close the gap and cause the sealing compound to form a seal between the vertical faces of the blocks  20 , as will be described in more detail below. This process is repeated to form the first course  122  of blocks along the required length of the inner wall  100 . 
     A support bracket  102  is then placed on top of the first course  122 , so that the downwardly extending fingers  110  of the support bracket  102  locate in the upper recesses  54  of each of the blocks  20  in the first course  122 . The mourning member  104  of the support bracket  102  is fixed to the inner wall  100  using screws, nails or another suitable method. 
     By virtue of this arrangement, each block  20  in the first course  122  is attached securely to the wall by the base bracket  112  and the support bracket  102 , as shown also in  FIG. 16 . 
     Another bead of sealing compound is applied to the groove  62  in the upper face of the blocks  20  of the first course  122 . The second course  124  of blocks  20  is then laid on top of the support bracket  102 , in a similar way to the first course  122 , so that the sealing compound forms a seal between the first course  122  and the second course  124  of blocks  20 , as well as between each neighbouring block  20  in the second course  124 . 
     The upwardly extending fingers  108  of the support bracket  102  locate in the lower recesses  56  of each of the blocks  20  in the second course  124 . This arrangement ensures that the second course  124  is in alignment with the first course  122 . 
     Further courses of blocks  20  are then added by repeating the process used to form the second course  124 . In this way, each block  20  in the second and higher courses of blocks  20  is held by the support, brackets  102  above and below each block  20 . 
     As shown most clearly in  FIG. 18 , the base bracket  112  and support brackets  102  are dimensioned so that a cavity  126  is formed between the blocks  20  and the inner wall  100 . Moisture that passes through the blocks  20  of the cladding can evaporate from the cavity  126  to ensure that the inner wall  100  remains dry. The cavity  128  also increases the thermal insulating properties of the clad wall. 
     Referring back to  FIG. 4 , the body  22  of each block  20  includes a cutaway  90  in its bottom face. The cutaway  90  is sufficient to accommodate the base member  106  of a support bracket  102 , so that when the block is mounted on the support bracket  102  in a second or higher course of blocks  20 , the front face  34  of the body  22  lines up alongside the front face  34  of the body  22  of the neighbouring block  20  in the course below and the grooves  82 ,  64  in the blocks  20  align to form a cavity  66  for the sealing material. 
     In this way, the bodies  22  of the blocks  20  in the cladding abut their respective neighbours, thereby forming an effectively continuous insulating cladding on the inner wall  100  with no gaps or so-called ‘cold bridges’ through the structure. 
     Referring to  FIG. 17 , the cutaway  90  extends across only a portion of the depth of the bottom face, so that a remaining portion (labelled ‘A’ in  FIG. 17 ) of the body abuts the top face of the body of the block below. By virtue of the body-to-body frictional contact across a region A of the fop and bottom faces, water penetration between the blocks is limited or prevented. Also, the abutting contact between the bodies over the contact region A ensures that the bodies of the blocks provide an uninterrupted thermal insulation layer behind the facings of the blocks. 
     The facings  24  of neighbouring blocks  20  are not, however, in load-transferring contact. Instead, a small gap (not shown) exists between neighbouring facings  24 , which may be achieved by ensuring that the facings  24  are somewhat smaller in area than the corresponding bodies  22 . This means that the relatively high weight of the facing  24  of a block is not carried by the facings of the blocks below. Rather, the weight of the facing  24  is transferred via the support brackets  102  to the inner wall  100 . 
     As described above, when neighbouring blocks  20  are assembled together to form a cladding for a wall or a similar structure, a sealing compound such as mastic, silicone sealant, putty or a similar material is applied between the blocks  20  to reduce further the amount of wafer and, particularly wind that can pass through the assembly of blocks  20 . In this embodiment of the invention, the grooves  82 ,  84  are adapted to ensure that the seal formed by the sealing material is particularly effective. It will be appreciated that such grooves could advantageously be provided in any type of building block, not just those described above. 
       FIG. 17  is an enlarged view of part of  FIG. 16 , showing the meeting point of two neighbouring blocks  20 A,  208  in adjacent courses. As shown also in  FIGS. 3 ,  4  and  7 , the top and left-hand side faces of the body  22  are provided with a generally U-shaped groove  82 . The bottom and right-hand side faces of the body  22  are provided with a generally W-shaped groove  64 ; that is, this groove  64  has a central projection or ridge, corresponding to the peak of the W, which extends along the length of the groove. 
     In use, a bead of sealing compound is applied to the groove  62 ,  84  of the first block  20 A, and the second such block  20 B is placed in a neighbouring relationship with the first block  20 A as described above. The grooves  62 ,  64  in the neighbouring blocks line up to define a cavity  66  for the sealing compound. 
     In  FIG. 17 , the U-shaped groove  62  in the top face of the lower block  20 A, into which the bead of sealing compound has been placed, is aligned with the W-shaped groove  64  in the bottom face of the upper block  20 B, so as to from the cavity  68  for the sealing compound. 
     The ridge of the W-shaped groove  64  projects inwardly into the cavity  68 . Thus, when the upper block  20 B is placed on top of the lower block  20 A, the ridge pushes into the sealing compound, squeezing it firmly against the walls of the cavity  68 . In this way, the sealing compound forms a substantially water-tight seal between the neighbouring blocks  20 A,  208 . 
     The cladding system can be readily adapted to clad an external corner.  FIG. 18  shows a course of blocks  20  at such a corner, viewed from above so that the support brackets  102  which is above the tops of the blocks  20  can be seen. 
     On one side of the corner, the course of blocks ends with an end block  20 A which extends beyond the wall  100  and the support bracket  102  by a distance equal to the depth of the cavity between the blocks and the wall  100  plus the depth of the body  22  of a block  20 . The end block  20 A is, however, identical to the block  20  shown in  FIG. 1 . 
     On the other side of the corner, the course of blocks ends with a corner block  20 B in which the body  228  has been cut away, as shown in  FIG. 19 , leaving its face  20 B extending beyond its body  228  by a distance equal to the depth of the body  22 B. As illustrated in  FIG. 16 , the end block  20 A and the corner block  20 B can be arranged so that their respective faces  24 A,  248  meet at the corner. 
     In this case, the body  22  of each block  20  is made from a cuttable material such as polystyrene. Therefore the body  22  can be easily cut away to form a corner block  208  such as that shown in  FIGS. 13 and 14 . Thus, it is not necessary to include specially-shaped blocks for corners and similar features in the cladding system. Conveniently, the blocks  20  may be provided with cutting guides, such as embossed lines on the rear, top and/or bottom faces of the body  22 , so that the blocks  20  may easily be converted to corner blocks  208  when required on-site. 
     It will be appreciated that the facings  24  of the blocks  20  can be decorative in nature. For example, the facings  24  could be textured, polished, coloured, coated, glazed, painted, printed or otherwise treated to provide a desired decorative effect. In this way, a cladding arrangement as shown in  FIGS. 13 to 19  can be made to have the appearance of, for example, a masonry wall. 
     The building block  220  shown in  FIG. 20  is an example of a building block according to the invention having a decorative facing  224 . In this case, a decorative effect has been applied to the facing  224  so that the facing  224  has the appearance of being made up of several small blocks  228 , separated by grooves  228 . The grooves  228  have the appearance of joints between the small blocks  226 . When a plurality of such blocks  220  are assembled into a cladding or wall, the resulting wall has the appearance of a dressed stone or ‘ashlar’ wall. In the illustrated example, four small blocks  226  are shown, but it will be appreciated that a different number of small blocks  228  could be present. 
     The grooves  228  may be formed by providing a suitable pattern on ridges on the mould shoe  90 , so that, when the mould shoe is pressed into the facing  224  during manufacture of the block  220  as described with reference to  FIGS. 8 and 9 , an impression of the ridges is left in the facing  224 . 
     In a variant of the building block  220 , the small blocks are separated by regions of the facing that are printed to give the appearance of grooves or joints between the small blocks, even though the facing is substantially planar in this variant. 
     In another variant, the facing of the block is given the appearance of wood shakes or shingles, for example by printing the facing or by applying a transfer to the facing which may optionally also be textured to give a grained effect and/or grooved to give the appearance of gaps between adjacent shingles. In still another variant, the facing of the block carries a primed or embossed logo or other graphic device. 
     When used in a cladding arrangement, the facings  24  of the blocks  20  provide a weather-deflecting skin to the cladding. In particular, the facings  24  deflect most of the incident water that falls on the cladding. In severe conditions, such as driving rain, some water may pass between the facings  24 . However, the abutment of the bodies of the blocks, along with the sealing material between the blocks  20 , helps to prevent water ingress past the bodies  22  of the blocks  20 . Even if water does pass behind the blocks  20 , the water enters the cavity  128  whereupon most of it evaporates. However, any residual water can drain down the channels  50  in the back of the blocks  20 . Drainage holes or slits are provided in the support brackets  102  to allow the water to pass the support brackets  102 , so the drained wafer can reach the base of the wall and soak away. 
     The cladding system also provides a highly-efficient method for thermally insulating a wall, by virtue of the cavity  128  between the inner wall  100  and the blocks  20 , the insulating material of the bodies  22  of the blocks  20 , and the absence of continuous heat-conducting features, sometimes known as thermal bridges, between the facings  24  of the blocks  20  and the wall  100 . These features, in combination, mean that the cladding system has a high R-value. 
     Another embodiment of a building block  320  according to the invention is shown in  FIGS. 21 to 24 . The building block  320  of  FIGS. 21 to 24  is similar to the building block  20  described with reference to  FIGS. 1 to 4 , and so only the differences will be described in detail. 
     The building block  320  comprises a body  322  of expanded polystyrene or a similar material, and a facing  324  of cementitious material attached thereto. The facing  324  is engaged with the body  322  by way of cooperating projections  332  of the facing and recesses  336  in the body  322 , as previously described with reference to  FIGS. 1 to 4 . 
     The body  322  is provided with upper and lower bracket-receiving recesses  354 ,  356  that cooperate with support brackets when the building block  320  is used in a cladding system, as previously described. Furthermore, as for the block of  FIGS. 1 to 4 , the body  322  is provided with grooves  382 ,  384  on the top, bottom and side faces thereof for receiving a bead of sealing material. 
     As can be seen most clearly in  FIG. 22 , in this embodiment, the rear face  360  of the body  322  is substantially planar, without drainage channels. The top face of the body  322  is provided with a plurality of inclined drainage slots or channels  352 , which run from the upper bracket-receiving recess  354  to the rear face  350  of the body  322 , and get deeper moving towards the rear face  350  of the body  322 . The drainage channels  352  intersect the rear face  350  so that the channels  352  act to direct wafer from the top face of the block  320  to the rear face  350 . In this embodiment, excess water can therefore flow down the rear face  350  of the body  322 . 
     A groove  351  extends along the entire length of the top face of the body  322 , parallel to the rear face  350 . The inclined channels  352  intersect the groove  351 , so that one portion  352   a  of each inclined channel  352  directs water into the groove  351 , and another portion  352   b  of each channel  332  directs water from the groove  351  towards the rear face  350 . The groove  351  helps to collect water that passes through the drainage holes, in the support brackets. 
       FIG. 25  show the block  320  of  FIGS. 21 to 24  mounted in a cladding system by two support brackets  102  of the type described with reference to  FIG. 14 . The upper bracket-receiving recess  354  receives the downwardly-extending fingers  110  of the bracket  102  positioned above the block  320 , and the lower bracket-receiving recess  358  receives the upwardly-extending fingers  108  of the bracket  102  positioned below the block  320 . 
     As in the previously-described embodiment, the body  322  is shaped so as to accommodate the base members  108  of the support brackets  102  in order that portions of the top and bottom faces of bodies of neighbouring blocks in adjacent horizontal rows can abut one another. However, in this case, both the top face and the bottom face of each body  322  includes a cutaway  390  having a depth that is approximately half of the thickness of the base member  106  of a support bracket  102 . 
     In this way, the base member  106  is accommodated between the bodies of neighbouring blocks in adjacent horizontal rows, in part in the cutaway  390  in the bottom face of the body  322  of the block  320  above the support bracket  102 , and in part in the cutaway  390  in the top face of the body  322  of the block  320  below the support bracket  102 . 
     Advantageously, the top and bottom faces of the block  320  of  FIGS. 21 to 24  are identical. In particular, both faces include cutaways  390 , inclined drainage channels  352 , and grooves  351 . This arrangement allows the blocks  320  to be installed either way up, which simplifies construction, it will be appreciated that the drainage channels  352  in the bottom face are not functional when the block  320  is in use in a cladding system. 
       FIGS. 28 to 28  show a variant of the building block of  FIGS. 21 to 24 , suitable for use as a corner block in a cladding system. The corner block  420  includes a body  422  having the same features as the body  322  of the block of  FIGS. 21 to 24 , as indicated by use of like reference numerals. 
     The facing  424  of the corner block  420  extends over the front face of the body  422  and around one of the side faces of the body  420 . Therefore the facing  424  incorporates a front face portion  424   a  and a side face portion  424   b  The end of the body  422  over which the side face portion  424   b  extends is shaped to include an inclined tape portion  470  and a narrow end face portion  472 . The back corner of the body  422 , between the end lace  472  and the rear face of the body  422 , is also shaped to include an overhand or chamfer  474 . Conveniently, when the body  422  is made from expanded polystyrene or a similar material, the end of the body can be hot wire-cut to form the desired shape  470 ,  472 ,  474 . 
     The front face portion  424   a  of the facing  424  is engaged with the body  422  by way of projections  432  on the facing  424  and corresponding recesses  336  as previously described. The side face portion  424   b  covers the inclined face portion  470  and the narrow end face portion  472 , and engages with the chamfer  474 . In this way, the facing  424  and the body  422  are held securely together. 
     The front and side face portions  424   a,    424   b  meet at an external corner  476  of the facing  424 . Because the inclined face portion  470  of the body  422  is set back from the corner  476 , the thickness of the facing  422  at the corner  476  is substantially thicker than elsewhere. This provides increased resistance to damage of the facing  422  at the corner  478  where it is particularly vulnerable to impact and other damage. 
     In use in a cladding system to clad around corner of a supporting wall, the corner block  420  can be used in a similar manner as described with reference to  FIGS. 18 and 19 . However, in this case, it is not necessary to cut any of the blocks on-site. Instead, the corner block  420  can be placed overhanging the corner of the supporting wall, and a block  320  of the type shown in  FIGS. 21 to 24  can be placed with one of its side faces in abutment with the back face of the overhanging portion of the corner block  420  to complete the cladding without interruption of the insulation provided by the block bodies  322 ,  422 . The corner blocks  420  can also be used to terminate the cladding in an attractive way, such as at window and door openings. 
     The dimensions of the corner block  420  are selected appropriately for the cladding system, for example, when the non-corner blocks  320  of the cladding system are 500 mm in length and 100 mm in thickness, a convenient size for the corner blocks  420  is 400 mm in length and 100 mm in thickness. 
     Another embodiment of the invention will now be described with reference to  FIGS. 29 to 32 . The cladding system of this embodiment, and the corresponding building block, is similar to the cladding system and building blocks of the other embodiments of the invention, and accordingly, only the differences will be described in detail. 
     As in the previously-described embodiments of the invention, the cladding system includes blocks  520  comprising a body  522  and a facing  524 . The facing  524  is engaged with to the body  522  by way of cooperating projections  540  of the facing  524  and recesses  536  in the body  522 , as previously described with reference to  FIGS. 1 to 4 . The body  522  is provided with upper and lower bracket-receiving recesses  554 ,  556  that cooperate with support brackets when the building block  520  is used in a cladding system, as previously described. Furthermore, as for the block of  FIGS. 1 to 4 , the body  522  is provided with grooves  562 ,  564  on the top, bottom and side faces thereof for receiving a bead of sealing material. 
     In this embodiment, the bracket-receiving recesses  554 ,  656  and the grooves  582 ,  564  on the side faces of the block  520  are inclined relative to the plane of the facing  524 . Specifically, each of the bracket-receiving recesses  554 ,  556  and the grooves  582 ,  564  on the side faces of the block  520  are closer to the facing  524  at the top of the block  520  than at the bottom of the block  520 . Additionally, the upper bracket-receiving recess  554  is closer to the facing  524  than the lower bracket-receiving recess  556 . 
     The body  522  of the block  520  is shaped so that, between the grooves  562 ,  564  and the front face  534  of the body  520  (to which the facing  524  is attached), the top and bottom faces of the body  522  are perpendicular to the plane of the facing  524 . Between the grooves  562 ,  564  and the rear face of the body  520 , the top and bottom faces of the body  520  are slightly inclined so as to lie in a plane that is at a small angle to the direction perpendicular to the facing  524 . The angle is such that the top edge of the rear face of the body  520  lies above the top edge of the facing  524 . 
     In this embodiment, the facing  524  is greater in height than the body  522 . In particular, a bottom end portion  524   a  of the facing  524  extends beyond the bottom face of the body  522 . The rearmost edge of the bottom end portion  524   a  of the facing  524  is radiused to define a curved edge  524   b  of the facing  524 . 
     As in the block shown in  FIGS. 1 to 4 , the top face of the body  520  includes a gutter  552  for drainage of water, and the bottom face includes a cutaway  590 . The gutter  552  and the cutaway  590  are similarly inclined with respect to the direction perpendicular to the facing  524 . 
       FIG. 30  shows a cladding system that includes blocks  520  of the type shown in  FIG. 29 . The blocks  520  are supported on an inner wall  100  by a plurality of support brackets  102  of the type described with reference to  FIGS. 13 to 16 . 
     The upper and lower bracket-receiving recesses  554 ,  556  of the blocks  520  receive, respectively, the downwardly-extending and upwardly-extending fingers  110 ,  108  of the brackets  102 . Because the top and bottom faces of the block are inclined, and because of the inclined and offset arrangement of the bracket-receiving recesses  554 ,  556 , each block  520  is supported on the wall  100  at an inclined angle. 
     As a consequence of this arrangement, when the blocks  520  are mounted as shown in  FIG. 3D , the bottom end portion  524   a  of the facing  524  of each block overlaps the top edge of the facing  524  of the adjacent block in the row below. This overlap gives an aesthetically pleasing effect, and also impedes further the ingress of water and air through the cladding system between neighbouring blocks  520  in adjacent rows. 
     The angle of inclination of the top and bottom faces of the body  522  of each block  520 . and the cutaway  500 , are such that the bodies  522  of adjacent blocks  520  abut one another in a face-to-face configuration, in this way. The advantageous thermal insulating and weather resisting properties of the cladding system that arise from the abutting bodies  522  of the blocks  520  are present in this embodiment of the invention, as in the other embodiments of the invention. 
     The angle of inclination of the grooves  582 ,  564  in the side faces of the blocks  520  is such that, when mounted as shown in  FIG. 30 , the grooves  562 ,  564  in the side faces of the blocks  520  extend vertically, parallel to the supporting wall  100 . In this way, the grooves  582 ,  564  in the top and bottom faces of each block  520  line up with the corresponding grooves in the adjacent blocks  520  in neighbouring rows so as to define a cavity for sealing material, as described above with reference to  FIG. 17 . 
       FIG. 31  shows a top view of the block  520  of  FIG. 29 . Compared to the block  20  shown in  FIG. 3 , the block  520  of this embodiment of the invention is wider. To give the blocks  620  an attractive appearance, randomly-spaced, vertically-extending lines or grooves  528  are provided in the front face of the facing  524 . 
     The grooves  528  extend part-way through the thickness of the facing  524 . To avoid introducing undesirable weaknesses in the cementitious or similar material of the facing  524 , each of the grooves  528  is positioned opposite one of the projections  540  on the rear face of the facing  524 . Because the material of the facing  524  is thicker in these regions, the presence of the grooves  528  does not unduly affect the mechanical stability of the facing  524 . 
     The appearance of the cladding system formed from the blocks  520  is shown in  FIG. 32 . The vertical grooves  528  in the facing  524  of each block  520  create the impression that the wall has been clad with units of a plurality of different widths, for example of a natural material, even though the blocks  520  are of uniform width. This effect, together with the overlapping facings  524  of the blocks  520  in neighbouring rows, gives the cladding an appearance similar to that of random wood shake siding or slates, if desired, the facings  524  of the blocks  520  can be textured or patterned to give a wood-grain or other decorative effect. 
     As in the previous embodiments of the invention, the facings  524  of neighbouring blocks in adjoining rows are not in load-transferring contact. Therefore the facings  524  need not be designed to support the weight of facings  524  of the blocks above, instead, the weight of each facing  524  is borne by the body  522  of the corresponding block, and the weight of each block  522  is borne substantially entirely by the supporting supporting brackets  102  and hence the supporting wall  100 . 
       FIG. 33  shows, schematically, a sequence of steps in a method of manufacturing a block  520  of the type shown in  FIGS. 29 to 32 . The method is similar to that described in  FIG. 8 , and only the details will be described in detail. 
     Starting with an empty pallet  80  ( FIG. 8(   a )), a plurality of block bodies  522  am arranged pa the pallet  80  ( FIG. 8(   b )) so that the recesses  532  are uppermost. The block bodies  522  include a sacrificial portion  522   a,  which can be seen in  FIG. 34 . 
       FIG. 34  is a side view of a block  520  in an intermediate stage of manufacture, in which the sacrificial portion  522   a  of the block body  522  is still attached to the body  522 . The sacrificial portion  522   a  extends to the bottom edge of the facing  524 , so as to support the bottom end portion  524   a  of the facing  524  during manufacture as will be described below. 
     Returning to  FIG. 33 , a mould frame  82  is placed around the bodies  522  ( FIG. 33(   c )). The facing  524  of the block is formed by pouring a settable material, such as a wet cementitious mix, into the mould frame  82  ( FIG. 33(   d )). The cementitious mixture is compacted by a mould shoe (not shown) as previously described. By providing suitable relief features on the mould shoe, the vertical grooves  528  and/or other desired decorative elements can be formed in the facings  524 . 
     At this stage, the sacrificial portion  522   a  of the each block body  522  supports the bottom end portion  524   a  of the facing  524 . The sacrificial portion  522   a  is also shaped to form the radiused edge  524   b  of the bottom end portion  524   a  (see  FIG. 34 ), or an alternative bottom edge profile if desired. The sacrificial portion  522   a  is preferably coated with a release agent or anti-stick treatment to prevent the material of the facing  524  from sticking to the sacrificial portion  522   a.  This allows easy removal of the sacrificial portion  522   a  at a later stage. The sacrificial portion  522   a  is conveniently formed separately from the remaining portion of the body  522 , and the two portions of the body  522 ,  522   a  are lightly glued or otherwise attached to one another before the bodies are placed on the pallet  80 . 
     As shown in  FIG. 33(   e ), the mould frame  82  is removed from the pallet  80 , to leave blocks  520  with the sacrificial portion  522   a  of each body  522  still present. Conveniently, the sacrificial, portion  522   a  can be left in place during storage and transportation, to protect the bottom edge portion  524   a  of the facing  524  from damage and to aid stacking and handling of the blocks  520 . Accordingly, the blocks  520  are removed from the pallet, with the sacrificial portions  522   a  attached, and stacked as shown in  FIG. 8(   f ) for storage and transportation. 
     The sacrificial portion  522   a  of the body  522  of each block car be removed on-site before the block  520  is used. In this way, the sacrificial portion  522   a  remains present for as long as possible to protect the bottom edge portion  524   a  of the facing. 
     Several variations and modifications, of the exemplary embodiments described above lie within the scope of the present invention as defined by the appended claims. 
     For example, the body of the block may be provided with projections for engagement with recesses in the facing. The facing need not be cast onto the body during manufacturing of the block but, with an appropriate configuration of recesses and projections, the facing could be manufactured as a separate component from the body and subsequently attached to the body to form the block. 
     The building blocks and other components can have any reasonable dimensions. For example, for typical construction applications, the blocks may be 600 mm in width and 300 or 450 mm in height. In such cases, the facing has a thickness of approximately 20 mm. although a thicker or thinner facing could be provided. In most cases, however, the minimum thickness of the facing is around 10 mm. 
     For given facing and body materials, the overall thickness of the block determines the degree of thermal insulation provided by the block. Typically, the overall thickness of a block is in a range from about 100 mm to about 240 mm, but thinner or thicker blocks could be provided. 
     When the blocks are to be manually handled, it is preferable that the overall mass of each block is less than 20 kg, this being the accepted maximum mass suitable, for single-person handling in the construction industry. The use of a lightweight body material helps to achieve this target, whilst allowing the block to be relatively large to enable rapid construction using the blocks. 
     The materials described above are not limiting. For example, as an alternative to expanded polystyrene, the body of the block may instead be made from phenolic resin or polyurethane. Indeed, the body of the block may be made from substantially any building material, and while it is advantageous in some applications for the body of the block to be lightweight and highly thermally insulating, these properties are not always essential. 
     Thus the body of the block could conceivably be made from concrete, stone, breeze block, or any other reasonable material. 
     When the body of the block is made from expanded polystyrene, as is preferred, the density of the expanded polystyrene can be chasers so as to optimise the properties of the block. Preferably, the density of the expanded polystyrene has a value in the range from about 18 kg m −3  to about 64 kg m −3  and more preferably the density of the expanded polystyrene has a value in the range from about 24 kg m −3  to about 40 kg m −3 . It will be appreciated that, as the density of the material increases, its mechanical properties, such as shear strength, compressive stress resistance and tensile strength, improve. Therefore, the choice of density depends on the mechanical and thermal properties required for a particular application. 
     The body material may be chosen to have good fire resistance. For example, when the body material is expanded polystyrene, a flame-retardant additive such as hexabromocyclododecane may be used to improve the fire resistance of the block. 
     Likewise, the facing of the block need not be made from a cementitious material, in embodiments of the invention which require the facing material to be settable, the facing could instead be made from a plastics melt or a curable resin material, providing that the facing material is chemically and thermally compatible with the material of the block. When the facing material does not need to be settable, the range of suitable materials extends further. 
     The density of the facing material affects the overall mass of the block, and also typically influences the mechanical properties of the facing. For example, the density of a typical concrete facing material has a value in the range from about 2000 kg m −3  to about 2400 kg m −3  but in some applications where the facing need not have a high mechanical strength, a lower-density concrete material could be suitable. 
     It will also be appreciated that several of the features of the various bodies, building blocks, cladding systems and components thereof described above can be used in isolation from one another or in combinations not explicitly described above. In particular, the interlocking arrangement of the facing and the body, the drainage channels on the rear of the block, the support bracket arrangement of the cladding system and the arrangement of grooves far the sealing material can all be used independently or in any combination in a building block or cladding system.