Set-downs, slab edges and the 10mm and 20mm limits on Truganina builds
Shower set-downs under the wall line, slab edges in the cavity and honeycombed concrete. What we measure when the frame first sits on the slab.
In short: A slab can be poured to the right strength and still cause trouble if its edges and set-downs are in the wrong place. Truganina frames have shown all three of the common problems.
Why the slab edge matters to the frame
The slab is poured to a set-out, and the frame is built to the plans. When the two disagree, something has to give. Either the frame hangs over the edge, losing bearing, or the slab sticks out past the frame and eats into the cavity behind the brickwork. Both show up at frame stage.
Set-downs that run under the wall
Wet areas are often poured with a set-down so the floor can fall to the waste. On a Truganina frame in July 2026 the concrete recess ran in under the wall frame, so the plasterboard would have no solid substrate at the base. In another bathroom the recess sat more than 10mm past the frame, which stops the plaster sitting flush. Trimming or extending is simple now, not later.
Honeycombing along the edge
Honeycombing is concrete with voids where the mix did not compact fully against the formwork. Along the slab edge it reduces strength and cover to the steel and can let water track in. We record where it is and how extensive, and the builder decides with their engineer how it is repaired.
The cavity behind the brick
A slab edge protruding more than 20mm beyond the frame narrows the cavity below the minimum. That gap is what keeps moisture on the brick side away from the timber. Trimming the slab back is the usual fix.
Measuring, not guessing
Every one of these items is a tape measure reading against a stated limit, which is what makes them hard to dispute. The report gives the measurement, the location and the reference.
Linking slab and frame stages
If you booked the slab inspection, the frame visit checks how the slab turned out after the pour. If you did not, frame stage is the earliest point we can see the edges and set-downs.
Written by our local inspection team from work carried out in Truganina. Licensed building practitioners, Building & Plumbing Commission registration CDB-U 53425.
