Fixing of Reinforcement — Position, Cover & Tolerance
Correctly bent bars are useless if fixed in the wrong place: IS 2502 covers fixing — tying bars in the designed position and spacing, supporting them on cover blocks/chairs to the IS 456 cover, holding tolerance, and making the cage rigid enough not to displace during concreting. Cover and position errors at fixing are a leading cause of durability failure and capacity loss.
Key Requirements
•Bars tied (binding wire / clips) in the designed position and spacing; cage rigid against displacement during pour
•Cover blocks/chairs to deliver the IS 456 nominal cover for the exposure (not bars on the formwork/ground)
•Position and spacing within the specified tolerance
•Top steel supported on chairs/spacers so it doesn't sag onto the soffit during concreting
•Check fixed cage against the BBS and drawings before pour (a hold point)
Practical Notes
✓Loss of cover at fixing is a top cause of reinforcement corrosion — cover blocks are cheap; a corroding structure is not.
✓Displaced top steel (no chairs) is a classic capacity loss in slabs/cantilevers — the steel ends up at the wrong effective depth.
Common Mistakes
⚠Bars laid on the formwork/ground with no cover blocks (zero cover, immediate durability failure).
⚠Top reinforcement not chaired — sags to the soffit, losing effective depth/capacity.
⚠No pre-pour check of the fixed cage against the BBS/drawings.