Inside corners and the bars that stop them cracking
Why every internal slab corner needs its own reinforcement.
In short: Re-entrant bars were missing at a Tallawong pre-pour inspection in August 2026.
Where the crack starts
Concrete shrinks as it cures. On an L shaped or stepped slab the shrinkage pulls hardest at each internal corner, and a crack runs diagonally out from it unless something holds it closed.
What the bars do
Re-entrant bars are short lengths of reinforcement laid across the corner at an angle. They do not stop shrinkage, they control it, keeping any crack fine instead of letting it open up.
What we found
At a Tallawong slab inspection in August 2026, internal corners had no re-entrant bars. The same visit found edge steel without its cover and mesh pressed against plumbing.
Required whether drawn or not
The National Construction Code calls for them at re-entrant corners. A drawing that leaves them off does not make them optional.
Cost of fixing
A few bars and some tie wire before the pour. After it, the remedy is monitoring a crack and arguing about its width.
Written by our local inspection team from work carried out in Tallawong. Licensed building practitioners, NSW Fair Trading licence 366177C.
