The traditional ‘in-ground’ concrete slab requires digging of trenches, construction of a perimeter nib wall and subsequent back filling. This method has a number of disadvantages:

  • It is labour intensive.
  • Rough cut trenches do not allow accurate measurement of concrete and considerable wastage can occur.
  • Construction can be subject to delays if rain occurs as the trench footings and reinforcing should be cleaned before concrete is poured.
  • If a perimeter nib wall is used a Block layer is generally required for its construction.
  • Three separate concrete pours could be needed: footings, nib wall, and the slab o Under floor insulation needs to be added a s a separate component.
  • Quality control is made more difficult due to the separate stages of construction.

The waffle raft slab system, on the other hand, involves building an ‘on-ground’ slab on a level building surface using perimeter formwork and expanded polystyrene Voidforms® , separated by plastic spacers , to create reinforced concrete ribs beneath the slab surface. This means the waffle raft slab system has a number of significant advantages over the conventional method of construction:

  • Construction is simple: there are fewer stages in construction.
  • Less site preparation is required, for example on non expansive soils only topsoil and organic. material must be removed.
  • Construction is quicker as there are fewer stages in construction and all stages can be carried out by one trade Work can often continue in adverse weather conditions. Recovery from heavy rain is quicker as there are no trenches to fill with water.
  • Concrete volumes can be accurately calculated meaning wastage can be eliminated. All concrete is contained within formwork and defined areas.
  • The Voidforms® provide ‘built in’ insulation.
  • Quality control is simple: everything is open for inspection prior to pouring concrete
  • Only one concrete pour is required.

Firth Corporate
Firth RibRaft Compliant