Cavity Former

Abstract

A cavity former for forming one or more cavities in a concrete slab, includes a hollow body ( 20 ) about which, during use of the former, poured concrete flows and subsequently cures to form a concrete slab in which the hollow body defines a cavity. The hollow body ( 20 ) has a first wall ( 27 ), a depending skirt wall ( 22 ) about the periphery of the first wall, and structure ( 24 ) defining, within the periphery, at least one depending hollow pillar formation ( 25 ) for in situ bracing the first wall to an underlying surface on which the skirt wall also rests.

1 . A cavity former for forming one or more cavities in a concrete slab, including: 
 a hollow body about which, during use of the former, poured concrete flows and subsequently cures to form a concrete slab in which the hollow body defines a cavity;    wherein said hollow body has a first wall, a depending skirt wall about the periphery of the first wall, and structure defining, within said periphery, at least one depending hollow pillar formation for in situ bracing said first wall to an underlying surface on which said skirt wall also rests.    
   
   
       2 . A cavity former according to  claim 1 , wherein said structure comprises a plurality of valleys in said first wall that define said at least one hollow pillar formation at their intersection.  
   
   
       3 . A cavity former according to  claim 1 , wherein said structure comprises a hollow tubular structure which constitutes said pillar formation.  
   
   
       4 . A cavity former according to  claim 2  wherein said hollow tubular structure has its interior open at said first wall.  
   
   
       5 . A cavity former according to  claim 1 , wherein said hollow body is configured to allow nesting of said cavity former with a second similar cavity former, and thereby to allow stacking of a multiplicity of said cavity formers.  
   
   
       6 . A cavity former according to  claim 5  wherein said skirt wall and said structure defining the hollow pillar formation are tapered to nest with the like features of a similar cavity former.  
   
   
       7 . A cavity former according to  claim 1 , wherein said hollow body further has a pair of intersecting upstanding ribs formed integrally on the outer surface of said first wall for supporting reinforcing mesh above said hollow body.  
   
   
       8 . A cavity former according to  claim 7  wherein said ribs are a pair of crossed ribs.  
   
   
       9 . A cavity former according to  claim 1 , wherein said skirt wall includes at least one outstanding tab for interlocking with a skirt wall of a similar cavity former so as to inhibit relative movement of individual cavity formers during pouring of the wet concrete.  
   
   
       10 . A cavity former according to  claim 1 , wherein said hollow body is a rectangular pod open on a lowermost side.  
   
   
       11 . A cavity former according to  claim 1 , wherein said cavity former has a plurality of hollow bodies or pods spaced apart by integrally formed channels that receive elongated slab-reinforcement.  
   
   
       12 . A cavity former for forming one or more cavities in a concrete slab, including: 
 a hollow body about which, during use of the former, poured concrete flows and subsequently cures to form a concrete slab in which the hollow body defines a cavity;    wherein said hollow body has a first wall, and a depending skirt wall about the periphery of the first wall, and is configured to allow nesting of said cavity former with a second similar cavity former, and thereby to allow stacking of a multiplicity of said cavity formers.    
   
   
       13 . A cavity former according to  claim 12  wherein said skirt wall and said structure defining the hollow pillar formation are tapered to nest with the like features of a similar cavity former.  
   
   
       14 . A cavity former for forming one or more cavities in a concrete slab, including: 
 a hollow body about which, during use of the former, poured concrete flows and subsequently cures to form a concrete slab in which the hollow body defines a cavity;    wherein said hollow body has a first wall, a depending skirt wall about the periphery of the first wall, and a pair of intersecting upstanding ribs formed integrally on the outer surface of said first wall for supporting reinforcing mesh above said hollow body.    
   
   
       15 . A cavity former according to  claim 14  wherein said ribs are a pair of crossed ribs.  
   
   
       16 . A cavity former for forming one or more cavities in a concrete slab, including: 
 a hollow body about which, during use of the former, poured concrete flows and subsequently cures to form a concrete slab in which the hollow body defines a cavity;    wherein said skirt wall includes at least one outstanding upturned tab for interlocking with a skirt wall of a similar cavity former so as to inhibit relative movement of individual cavity formers during pouring of the wet concrete.    
   
   
       17 . A cavity former according to  claim 16  wherein said interlocking is such that the plural interlocked cavity formers provide a moisture barrier between the concrete and an underlying ground surface.  
   
   
       18 . A cavity former according to  claim 12 , wherein said hollow body is a rectangular pod open on a lowermost side.  
   
   
       19 . A cavity former according to  claim 12 , wherein said cavity former has a plurality of hollow bodies or pods spaced apart by integrally formed channels that receive elongated slab-reinforcement.