Slab beams narrower than drawn
How loose waffle pods shrink the beams in a Sunbury slab, and how to catch it.
In short: A waffle slab relies on its beams. When pods move before the pour, beams end up narrower than designed and nobody sees it afterwards.
How a waffle slab works
Polystyrene pods form voids, and the concrete between them becomes a grid of beams. The width of those beams is part of the design.
What happened on a Sunbury slab
We measured one internal beam at about 50mm wide where the plans called for 110mm, and found a pod lying loose inside another beam.
Why pods move
They are light and often not fixed down. Wind, foot traffic and steel fixing all push them around.
Other slab items
Mesh touching pipes, vapour barrier draped over the steel and too few bar chairs all appeared on the same jobs.
Written by our local inspection team from work carried out in Sunbury. Licensed building practitioners, Building & Plumbing Commission registration CDB-U 53425.
