Slab steel on a Deanside build: what to check the day before the pour
Rib bars, cover, trimmers and the vapour barrier on a waffle raft, checked while they can still be fixed.
In short: A waffle raft slab is only as good as the steel inside it. The day before the pour is the only chance to look.
Why the day before
Once concrete is placed, nobody can see the steel, the pods or the membrane again. The day before the pour is when the concreter has finished and the inspector can measure everything.
Extra bars in wide ribs
Engineering often calls for extra top and bottom bars when a load-bearing rib is wider than the standard width. Missing bars are one of the most common slab findings near Deanside.
Cover under and beside the steel
Bar chairs hold the steel off the ground so concrete surrounds it. Too little cover lets moisture reach the steel, which rusts and expands over the years.
Penetrations and trimmers
Where plumbing pipes come through the slab, the mesh is cut. Trimmer bars around the cut restore its strength, and the mesh must stay 25mm clear of the pipes.
The vapour barrier
The membrane under the slab keeps ground moisture out. Punctures need patching with polyethylene and tape, and it must lie beneath the steel, not over it.
Written by our local inspection team from work carried out in Deanside. Licensed building practitioners, Building & Plumbing Commission registration CDB-U 53425.
