AU2014277653B1

AU2014277653B1 - Creation of Curved or Circular Hobs in Cast-in-Situ Concrete Slabs

Info

Publication number: AU2014277653B1
Application number: AU2014277653A
Authority: AU
Inventors: Antonio Pantano
Original assignee: Pantano Investments Pty Ltd
Current assignee: Pantano Investments Pty Ltd
Priority date: 2014-12-10
Filing date: 2014-12-10
Publication date: 2016-03-24
Anticipated expiration: 2034-12-10

Abstract

A mould for creating on a concrete building slab a sill or hob having a partial or wholly curved planform; various means being employed to effect curvature of said mould by increasing and/or decreasing in length appropriate elements of said mould; said mould 5 being supported on chairs fixed to formwork for the building of said concrete building slab, with its installation being integrated with fixing of the steel reinforcing bar of said concrete slab and its filling with concrete being integrated with the pouring of said concrete slab; or said mould being fixed to the upper surface of a previously-cast concrete building slab; or said mould being fixed to said formwork to create a permanent 10 edge for said concrete slab.

Description

ORIGINAL Australia Patents Act 1990 Complete Specification for the Invention Entitled CREATION OF CURVED OR CIRCULAR HOBS IN CAST-IN-SITU CONCRETE SLABS The invention is described in the following statement: 2 CREATION OF CURVED OR CIRCULAR HOBS IN CAST-IN-SITU CONCRETE SLABS This invention relates generally to the provision, as part of the building construction process, of curved or circular sills or hobs in cast-in-situ concrete slabs. 5 More particularly, it relates to moulds for the casting of such sills or hobs which are made integrally with cast in-situ concrete building slabs or applied to the surface of previously-cast concrete building slabs. Particularly in the construction of multi-storey buildings, it is common to provide raised sills or hobs of some form to cast in-situ concrete slabs. Such sills or hobs may 10 act as supports for building elements such as window frames, curtain wall panels and the like, providing a watertight barrier beneath such building elements to prevent the ingress of water. Said building elements may incorporate lower frames or sills that bear directly upon and are sealed to a supporting surface such as a cast in-situ concrete slab. These commonly take the form of simple or complex metal sections or solid timber sections. 15 In other applications, separate sills or hobs of similar form are sealing fixed to a said supporting surface and said building elements are fixed to and supported by said sills or hobs. In yet other applications, surface-mounted concrete sills or hobs are formed on the upper surface of said cast in-situ concrete slabs to support said window frames, 20 curtain wall panels and the like. In these applications, box moulds which are more or less open at the top and bottom are fixed to concrete slabs in appropriate positions, filled with concrete and the concrete allowed to cure. Said sills or hobs are then waterproofed appropriately and said building elements then fixed to them. The separate forming of said sills or hobs on cast in-situ concrete slabs is inefficient and time consuming, 25 requiring the re-attendance of several building trades personnel to a building site to 3 accurately measure up and fix said moulds in position and then to fill them with concrete. Additionally, irregularities in the trowelled surfaces of said cast in-situ concrete slabs may require the removal of concrete in order for said moulds to be set at the correct level. Not only is the construction of formwork a time-consuming process 5 requiring the services of skilled personnel but, after curing of a concrete slab, the formwork must be stripped out and discarded, thereby incurring further expenditure of labour and loss of value. There is often no quality control of the concrete used in the separate creation of such sills or hobs, said concrete often being mixed on site, and cracking may occur as a result of fixing window frames, curtain wall panels and the like 10 to them. Additionally, in the forming of surface-mounted sills or hobs on concrete building slabs, it is usual to fix anchors in the form of short, upstanding lengths of reinforcing bar into said concrete building slab, the upper parts of said anchors being subsequently embedded in said sill or hob. Said anchors are normally bonded into bores drilled into said concrete building slab using epoxy resin. However, it is known that 15 unconscientious workers frequently simply hammer anchors into said bores, confident in the fact that the dereliction will be concealed by said sill or hob. In the drilling of said bores, the possibility exists of damaging reinforcing bar or post-tensioned cables embedded within said concrete building slab. Where said sills or hobs are required to be curved, circular or part-circular in 20 form and are required to be surface-mounted on a previously-cast concrete building slab, wooden moulds or forms for their formation are normally created by carpenters. Apart from the risks associated with the fixing of said anchors and the subsequent wastage of said moulds or forms, considerable skill is required in locating, shaping and setting the correct levels of said moulds or forms. When it is considered that a multi-storey 25 building may require several thousand lineal metres of such sills or hobs, the magnitude 4 of the inefficiency, the loss of time caused and the cost will be readily appreciated. The first object of the present invention is to provide a system that permits installation of sill or hob forming moulds to be integrated into the process of fixing steel reinforcing bar preliminary to the pouring of concrete building slabs, and with the 5 process of filling said sill or hob moulds with concrete being integrated into the process of in-situ casting of concrete building slabs; said moulds providing sills or hobs of circular, regularly-curved or irregularly-curved planform. The second object of the present invention is to provide sill or hob forming moulds that are fixed to the upper surfaces of previously-cast concrete building slabs for the purpose of providing sills or 10 hobs of circular, regularly-curved or irregularly-curved planform. According to the present invention, a sill or hob mould comprises two elongated, flat, parallel side panels maintained in spaced-apart relationship by a plurality of spacer members welded to them, said spacer members being of open or closed form and optionally taking the form of straight or bent rods, bars, struts, cruciform members, flat 15 or corrugated plates, tubular sections or the like. To stiffen said side panels, their upper and lower edges are folded inwardly through an angle of 90 degrees to create upper and lower first returns orientated normal to said side panels, part of each said first return then being folded inwardly through 90 degrees to create upper and lower second returns orientated parallel to said side panels, the final width of said first returns falling in the 20 range 0.1 to 0.3 of the width of said side panels and the final with of said second returns falling in the range 0.5 tol.5 of the width of said first returns. In the preferred embodiment, said spacer members are welded to the opposed faces of said second returns, said welding taking the form of gas, arc or spot welding. In alternative embodiments, said spacer members are welded to the internal surfaces of said side 25 panels. In the preferred embodiment, the longitudinal spacing of said spacer members 5 (with reference to the longitudinal axis of said mould) falls in the range 0.5 to 2.0 of the height of said side members. Also in the preferred embodiment, the longitudinal width of said spacer members (with reference to the longitudinal axis of said mould) falls in the range 0.1 to 0.25 of the height of said side members. Also in the preferred 5 embodiment, said spacer members are optionally orientated (with reference to the longitudinal axis of said mould) at an angle falling in the range 90 degrees to 45 degrees. In an alternative embodiment, tabs or other localised extensions are provided formed on the sides of said spacer members to provide a greater choice of locations for the fixing of said spacer members to said second returns. The transverse width of the aperture 10 between the inner faces of said second returns and the longitudinal width of said spacer members is such that concrete is able to enter from above and pass through said mould to formwork below upon which a parent concrete building slab is to be formed, thereby making the concrete within said filled mould contiguous and monolithic with that of said parent concrete slab beneath. 15 In a first embodiment, said mould is supported upon a plurality of discrete chairs each having a baseplate welded to its lower end, said baseplates being fixed to said formwork; said chairs being made rigid or adjustable in height and having supporting plates welded to their upper ends, said mould being fixed to said supporting plates by welding or by the fixing to said upper second returns of upwardly extending pairs of 20 attachment plates welded to said supporting plates, said attachment plates entering between said spacer members and with the outer surfaces just contacting the inner surfaces of said second returns. Said supporting plates are optionally welded to said upper second returns or fixed to them by means of suitable fastenings. In a second embodiment, said mould is fixed to the upper surface of a previously-cast concrete 25 building slab. In this embodiment, holes are drilled into said concrete building slab and 6 Loxin@-type masonry anchors are installed in said holes, tightening of the nuts of said masonry anchors urging bridge members against said lower first returns, thereby urging said mould against said concrete building slab upper surface. In the preferred embodiment, said bridge members comprise a stiff, strong body part extending 5 transversely across the width of said mould, the ends of said body part being turned through 90 degrees to form downwardly-projecting parts that bear against said lower first returns. The ends of said downwardly-projecting parts are optionally provided with shoes of a suitable material or are otherwise widened in some way to increase their contact area with said lower first returns. 10 In a third embodiment, where all or part of said mould is required to have a curved planform, transverse cuts are made through said upper and lower first and second returns, said cuts permitting said mould to be bent around a suitable former, said cuts opening or closing depending upon the mode of said bending. To permit the bend radii normally expected to be employed in normal architectural applications of said mould, 15 the width of said cuts falls in the range 2.0 to 5.0 millimetres, depending upon the spacing width of said cuts. In the preferred embodiment, the longitudinal spacing width of said cuts (with reference to the longitudinal axis of said mould) normally falls in the range 0.75 to 3.0 of the width of said first returns. In a first alternative embodiment, said cuts, in a bent form of said mould, are locked together one to another by weld nuggets. 20 In a second alternative embodiment, a strip of metal shaped to conform to the planform shape of one or both said first returns of a curved part of said mould is spot-welded or otherwise fixed over said curved part. In a fourth embodiment, a section of said mould is made curved by expanding and contracting said upper and lower, first and second returns by knurling or by insertion 25 of a closely-spaced series of indentations.

7 Where said mould is to be made integral with a concrete building slab, it supported from formwork for the making of said concrete slab upon a row of discrete chairs, the height of which positions said mould such that its lower edge is set at the intended surface level of said concrete building slab. Said chairs remain embedded in 5 said concrete building slab after it is poured. In the preferred embodiment, curved or straight sections of said mould are joined end-to-end by welding. The various aspects of the present invention will be more readily understood by reference to the following description of preferred embodiments given in relation to the accompanying drawings in which: 10 Figures 1, 2, 3 and 4 depicted typical sills or hobs of curved planform, slotted sections being indicated only schematically; Figure 5 is a short length of a sill or hob of curved planform; Figure 6 is a view from the side edge of a spacer member having tabs or localised extensions provided on its side edges; 15 Figure 7 is a transverse cross-sectional view of a first embodiment of said mould; Figure 8 is a transverse cross-sectional view of a second embodiment of said mould; Figure 9 is a view from above or below, in an alternative embodiment of 20 said mould, of an edge of said side panel following said first bend; Figure 10 is a view of the first return of a said side panel of the embodiment of Figure 9 following the insertion of indentations; Figure 11 is a view of the second return of a said side panel of the embodiment of Figure 9 following the insertion of indentations. 25 The various figures are drawn to a number of different scales and no inference 8 should be drawn from this. With reference to Figure 7, a sill or hob mould 10 comprises two elongated, flat, parallel side panels 8 maintained in spaced-apart relationship by a plurality of spacer members 9 welded to them, said spacer members being of open or closed form and 5 optionally taking the form of straight or bent rods, bars, struts, cruciform members, flat or corrugated plates, tubular sections or the like. To stiffen said side panels, their upper and lower edges are folded inwardly through an angle of 90 degrees to create upper 11 and lower 12 first returns orientated normal to said side panels, part of each said first return then being folded inwardly through 90 degrees to create upper 13 and lower 14 10 second returns orientated parallel to said side panels, the final width of said first returns falling in the range 0.1 to 0.3 of the width of said side panels and the final width of said second returns falling in the range 0.5 tol.5 of the width of said first returns. In the preferred embodiment, said spacer members are welded to the opposed faces of said second returns, said welding taking the form of gas, arc or spot welding. In alternative 15 embodiments, said spacer members are welded to the internal surfaces of said side panels. In the preferred embodiment, the longitudinal spacing of said spacer members (with reference to the longitudinal axis of said mould) falls in the range 0.5 to 2.0 of the height of said side members. Also in the preferred embodiment, the longitudinal width of said spacer members (with reference to the longitudinal axis of said mould) falls in 20 the range 0.1 to 0.25 of the height of said side members. Also in the preferred embodiment, said spacer members are optionally orientated (with reference to the longitudinal axis of said mould) at an angle falling in the range 90 degrees to 45 degrees. With reference to Figure 6, in an alternative embodiment, tabs 15 or other localised extensions are provided formed on the sides of spacer members 9 to provide a 25 greater choice of locations for the fixing of said spacer members to said second returns.

9 The transverse width of the aperture between the inner faces of said second returns and the longitudinal width of said spacer members is such that concrete is able to enter from above and freely pass through said mould to formwork below upon which a parent concrete building slab is to be formed, thereby making the concrete within said filled 5 mould contiguous and monolithic with that of said parent concrete slab beneath. Where said mould is to be fixed in place concurrently with the fixing of the reinforcing bar of a concrete building slab it is supported upon a plurality of discrete chairs 3 each having a baseplate 4 welded to its lower end, said base plates being fixed to formwork 7 by suitable fastenings (typical positions indicated as 6); said chairs being 10 made rigid or adjustable in height and having supporting plates 16 fixed by welds 17 to their upper ends, said mould being fixed to said supporting plates by welds 18. The height of said chairs is such that said mould is supported above said formwork with its lower edge at the intended surface level of said concrete building slab. Said chairs remain embedded in said concrete building slab after it is poured. 15 With reference to Figure 8, in an alternative embodiment, upwardly extending pairs of attachment plates 19 are welded to supporting plates 16, said attachment plates entering between said spacer members with the outer surfaces of said attachment plates just contacting the inner surfaces of second returns 13, 14. Said supporting plates are optionally welded to said upper second returns or fixed to them by means of suitable 20 fastenings (typical positions depicted in broken line as 20). The extension of said attachment plates into said mould provides a reinforcement effect to said mould which acts to prevent cracking of said sill or hob. In an alternative embodiment (not shown), said mould is fixed to the upper surface of a previously-cast concrete building slab and is filled with concrete. In this 25 embodiment, holes are drilled into said concrete building slab and Loxin@-type masonry 10 anchors are installed in said holes, tightening of the nuts of said masonry anchors urging bridge members against said lower first returns, thereby urging said mould against said concrete building slab upper surface. In the preferred embodiment, said bridge members comprise a stiff, strong body part extending transversely across the width of said mould, 5 the ends of said body part being turned through 90 degrees to form downwardly projecting parts that bear against said lower first returns. The ends of said downwardly projecting parts are optionally provided with shoes of a suitable material or are otherwise widened in some way to increase their contact area with said lower first returns. With reference to Figures 1, 2, 3, 4 and 5 where all or part of a said mould is 10 required to have a curved planform, transverse cuts 1, 2 are made through said upper and lower first and second returns, said cuts permitting said mould to be bent around a suitable former (not shown), said cuts opening or closing depending upon the mode of said bending. To permit the bend radii normally expected to be employed in normal architectural applications of said mould, the width of said cuts falls in the range 2.0 to 15 5.0 millimetres, depending upon the spacing width of said cuts. In the preferred embodiment, the longitudinal spacing width of said cuts (with reference to the longitudinal axis of said mould) normally falls in the range 0.75 to 3.0 of the width of said first returns. In a first alternative embodiment (not shown), in a bent form of said mould, segments 21 of said first returns created by said cuts are locked together one to 20 another by weld nuggets (not shown). In a second alternative embodiment (not shown), a strip of metal shaped to conform to the planform shape of one or both said first returns of a curved part of said mould is spot-welded or otherwise fixed to segments 21 to lock them in their curved arrangement. Where the desired attachment positions of a spacer member coincides fully or partially with a cut 1, 2 (as depicted as 22 in Figure 5), the 25 spacer member of Figure 6 is optionally employed to provide a greater choice of 11 locations for the fixing of said spacer member to said second return. Where necessary, straight 27 and curved 28 sections of said mould are butt-jointed together by welding or by sleeves (not shown) making a neat fit inside the abutting ends of two lengths of said mould, said sleeves acting to maintain said abutting ends in alignment until said mould 5 is filled with concrete. With reference to Figures 9, 10 and 11, where all or part of a said mould is required to have a curved planform, that part of said mould requiring expansion is expanded by knurling of said upper and lower, first and second returns and that part requiring contraction is contracted by insertion of a closely-spaced series of indentations 10 in said upper and lower, first and second returns. In this embodiment, prior to the joining of said inner and outer side panels of said mould, where a contraction of said upper and lower, first and second returns is required, a series of suitably spaced holes or apertures 23 is made in said side panels a suitable distance from their upper and lower edges. Said upper and lower edges are then folded inwardly through 90 degrees, the 15 width of the folded part being equal to the combined widths of said first and second returns, said holes or apertures being situated on the line of division between said first and second returns. Second returns 13, 14 are then created by folding though a further 90 degrees. Suitably shaped, hardened steel rollers then insert tapered indentations (wider towards said second returns) into said first returns and, simultaneously, parallel 20 indentations into said second returns, insertion of said indentations causing the relevant said side panel to adopt a curved shape, the presence of said holes or apertures acting to prevent interference between the opposed ends of said curved and parallel indentations. During insertion of said indentations, said first and second returns are supported by an internally-positioned, hard elastomer block, said block supporting the surrounding 25 material while permitting said indentations to be made. To support said side panels 12 against loadings imposed by said indentation rollers, supporting rollers or metal shoes abut the upper and lower edges of said side panels during said indentation process. Where an expansion of said upper and lower first and second returns is required, hard metal knurling rollers are run over the appropriate surfaces. In knurling said upper and 5 lower first returns, the knurling effect applied by said knurling rollers tapers from greatest towards said second returns to minimal at said side panels. In the preferred embodiment, supporting rollers or metal shoes abut the upper and lower edges of said side panels to support them against loadings imposed by said indentation or knurling rollers. 10 In an alternative embodiment (not shown), said transverse cuts are made only through said first returns and said parallel indentations are made, or said knurling applied, only in said second returns, the insertion of said parallel indentations or application of said knurling in said second returns causing said cuts to open or close up, thereby causing the relevant said side panel to adopt a curved shape. It will be 15 appreciated that said indentation and knurling method and said method involving only making said transverse cuts through said first returns will result in preservation of a greater strength in said mould. In an alternative embodiment (not shown), said mould is positioned at the edge of formwork to be employed for the building of a concrete building slab and is fixed 20 directly to said formwork. In this embodiment, said mould is secured to said formwork by a plurality of suitable fastenings passing through a plurality of bridge members into said formwork, tightening of said fastenings urging said bridge members against said lower first returns, thereby urging said mould against said formwork upper surface. In the preferred embodiment, said bridge members comprise a stiff, strong body part 25 extending transversely across the width of said mould, the ends of said body part being 13 turned through 90 degrees to form downwardly-projecting parts that bear against said lower first returns. The ends of said downwardly-projecting parts are optionally provided with shoes of a suitable material or are otherwise widened in some way to increase their contact area with said lower first returns. Said mould is made with a 5 height equal to the thickness of said concrete building slab and, when said mould is filled with concrete and said concrete building slab is poured, said mould forms a permanent edge of said concrete building slab. In an alternative embodiment (not shown), said mould is temporarily buttressed by or fixed to an upright board or supporting panel fixed to the edge of said formwork, said board or supporting panel 10 being braced by props supported from outriggers fixed to the underside of said formwork. In another alternative embodiment (not shown), said mould is made to incorporate strong mounting pieces welded between the inner surfaces of upper second returns 13 and positioned more or less flush with upper first returns 11, said spacer 15 pieces incorporating threaded apertures or threaded bushes to facilitate attachment of balustrade stanchions or the like. In another alternative embodiment (not shown), drain pieces in the form of tubular members of suitable length passing transversely through said mould to permit drainage of water impounded by said sill or hob. Said drainage members are made from 20 any suitable, non-corrodible material and extend a suitable distance from said mould to carry water clear said mould. Said drainage members are optionally fixed into place through the use of suitable fastenings or bonding materials or frictionally retained in place until said mould is filled with concrete. 25

Claims

1. A mould for creating on a concrete building slab a sill or hob having a partial or wholly curved planform; said mould comprising two elongated, flat, parallel side panels maintained in spaced-apart relationship by a plurality of spacer members fixed to them by welding, said spacer members being of open or closed form and optionally taking the form of straight or bent rods, bars, struts, cruciform members, flat or corrugated plates, tubular sections or the like; said side panels being stiffened by their upper and lower edges being folded inwardly through an angle of 90 degrees to create upper and lower first returns orientated normal to said side panels, part of each said first return then being folded inwardly through 90 degrees to create upper and lower second returns orientated parallel to said side panels; said mould being supported upon a plurality of discrete chairs of closed cross-section, each having a baseplate welded to its lower end, said base plates being fixed to formwork for the making of said concrete slab, said chairs being made rigid or adjustable in height and having supporting plates fixed by welding to their upper ends, said mould sitting upon said supporting plates and being secured in place by welding; curvature of said mould being created by increasing and decreasing in length of said upper and lower first and second returns by the cutting of transversely-arranged slotting or by their knurling or indentation; said mould and chair being adapted such that their installation is able to be integrated with fixing of the steel reinforcing bar of said concrete slab by the same trade personnel and its filling with concrete able to be integrated with the pouring of said concrete slab by the same concreting personnel; said curved sill or hob providing a raised, peripheral edge for said concrete slab; said mould being, effectively, permanent formwork and remaining in place as part of 15 said curved sill or hob after its filling with concrete.

2. The mould of Claim 1 which incorporates drainage provisions to be incorporated into said sill or hob, said drainage provisions taking the form of tubular members of suitable length passing transversely through said mould to permit drainage of water impounded by said sill or hob, said drainage members being made from any suitable, non-corrodible material and extending a suitable distance from said mould to carry water clear of said sill or hob, said drainage members being fixed into place through the use of suitable fastenings or bonding materials or frictionally retained in place until said mould is filled with concrete.

3. The mould of Claim 1 which incorporates attachment provisions to be incorporated into said sill or hob, said attachment provisions taking the form of strong mounting pieces welded between the inner surfaces of said upper second returns of said mould and positioned more or less flush with said upper first returns of said mould, said spacer pieces incorporating threaded apertures or threaded bushes.

4. The mould of Claim 1 in which the final width of said first returns falls in the range 0.1 to 0.3 of the width of said side panels and the final width of said second returns falls in the range 0.5 tol.5 of the width of said first returns.

5. The mould of Claim 1 in which said spacer members are fixed by welding to the opposed faces of said second returns or to the internal surfaces of said side panels, said welding taking the form of gas, arc or spot welding.

6. The mould of Claim 1 in which the longitudinal spacing of said spacer members (with reference to the longitudinal axis of said mould) falls in the range 0.5 to 2.0 of the height of said side panels.

7. The mould of Claim 1 in which the longitudinal width of said spacer members 16 (with reference to the longitudinal axis of said mould) falls in the range 0.1 to 0.25 of the height of said side panels.

8. The mould of Claim 1 in which said spacer members are orientated (with reference to the longitudinal axis of said mould) at an angle falling in the range 90 degrees to 45 degrees.

9. The mould of Claim 1 in which the transverse width of the aperture between the inner faces of said second returns and the longitudinal width of said spacer members is such that concrete is able to enter from above and freely pass through said mould to formwork below upon which a parent concrete building slab is to be formed, thereby making the concrete within said filled mould contiguous and monolithic with that of said parent concrete slab beneath.

10. The mould of Claim 1 in which said spacer members are provided with tabs or other localised extensions on their side edges to provide a greater choice of locations for the fixing of said spacer members to said second returns, said tabbed spacer member being employed where its desired attachment position coincides fully or partially with a said transverse cut made through a said second returns.

11. The mould of Claim 1 in which, to permit the bend radii normally expected to be employed in normal architectural applications, the width of said transversely arranged slotting falls in the range 2.0 to 5.0 millimetres.

12. The mould of Claim 1 in which the longitudinal spacing width of said transversely-arranged slotting (with reference to the longitudinal axis of said mould) normally falls in the range 0.75 to 3.0 of the width of said first returns.

13. The mould of Claim 1 in which, in a curved section of said mould, segments of said first returns created by said transversely-arranged slotting are locked 17 together one to another by weld nuggets.

14. The mould of Claim 1 in which a strip of metal shaped to conform to the planform shape of one or both said first returns of a curved part of said mould is spot-welded or otherwise fixed to said segments to lock them into their curved arrangement.

15. The mould of Claim 1 in which, where parts of said mould are required to be decreased in length for the purpose of creating curvature, said upper and lower first and second returns have inserted into them a closely-spaced series of indentations, said indentations being inserted prior to the joining of said inner and outer side panels of said mould.

16. The mould of Claim 15 in which, prior to forming of said upper and lower first and second returns a series of suitably spaced holes or apertures is made in said side panels a suitable distance from their upper and lower edges, said upper and lower edges then being folded inwardly through 90 degrees, the width of the folded part being equal to the combined widths of said first and second returns, said holes or apertures being situated on the line of division between said first and second returns, said second returns then being created by folding though a further 90 degrees; suitably shaped, hardened steel rollers then inserting tapered indentations (wider towards said second returns) into said first returns and, simultaneously, parallel indentations into said second returns, insertion of said indentations causing said side panel being worked on to adopt a curved shape, the presence of said holes or apertures acting to prevent interference between the opposed ends of said curved and parallel indentations; during insertion of said indentations, said first and second returns being supported by an internally positioned, hard elastomer block, said block supporting the surrounding material 18 while permitting said indentations to be made, supporting rollers or metal shoes abutting the upper and lower edges of said side panels to support them against loadings imposed by said indentation rollers.

17. The mould of Claim 1 in which, where parts of said mould are required to be increased in length for the purpose of creating curvature, after forming of said upper and lower first and second returns, hard metal knurling rollers are run over the appropriate surfaces of said returns, the knurling effect applied by said knurling rollers tapering from greatest towards said second returns to minimal at said side panels.

18. The mould of Claim 1 in which upwardly extending pairs of attachment plates are welded to said supporting plates, said attachment plates entering between said spacer members with the outer surfaces of said attachment plates just contacting the inner surfaces of said second returns; said supporting plates being welded to said upper second returns or fixed to them by means of suitable fastenings; the extension of said attachment plates into said mould providing a reinforcement effect which acts to prevent cracking of said sill or hob.

19. The mould of Claims 1, 15 and 17 in which said transverse slotting is cut through only said first returns and said indentations are inserted in or said knurling is applied to only said second returns, the insertion of said indentations or application of said knurling causing said cuts to open or close up, thereby causing the relevant said side panel to adopt a curved shape.

20. The mould of Claim 1 which is made with a height equal to the thickness of said concrete building slab and, when said mould is filled with concrete and said concrete building slab is poured, said hob and mould form a permanent edge of said concrete building slab.