Bar chairs, laps and ties before a pour
What a slab pre-pour inspection checks in the steel, using findings from nearby Cranbourne East.
In short: A slab's strength depends on steel sitting in the right place inside the concrete. Chairs, laps and ties are how it gets there.
Steel has to be held up
Mesh and bars sit on chairs so the concrete can flow underneath and cover them. Too few chairs and the steel gets pushed down as people walk on it during the pour.
What we recorded
On a slab in Cranbourne East, close to Pakenham, edge beam steel had too few chairs and some sprayed on supports where proper ones were needed. Mesh between the pods also needed more support.
Laps and ties
Where mesh sheets or bars meet they must overlap by a set length and be tied. Untied steel at corners and crossings moves when the concrete is vibrated.
The vapour barrier
The same slab had the barrier stopping short of ground level in the edge beam. It is meant to run continuously under the slab and down the beams.
Timing
All of this is checked the day before the pour. The next day it is inside the concrete for good.
Written by our local inspection team from work carried out in Pakenham. Licensed building practitioners, Building & Plumbing Commission registration CDB-U 53425.
