Roof Slab Concreting Checklist: Before, During and After the Pour

Before the pour

Formwork

• Shuttering level and at correct height; camber if specified.
• Props plumb, at specified spacing, on firm base plates or sole plates.
• Joints tight — no gaps for slurry to leak.
• Shuttering oil applied; surface cleaned of debris, wire and sawdust.

Reinforcement

• Bar sizes, spacing and number match the structural drawing.
• Laps and anchorage lengths as specified; laps staggered.
• Cover blocks of the correct thickness under bottom bars and at edges.
• Chairs holding top steel at the right height.
• Steel clean — no loose rust, mud or oil.
• Engineer's inspection and approval recorded.

Services

• Electrical conduits and junction boxes fixed and taped.
• Plumbing sleeves for pipes placed.
• Fan hooks and any embedded fixtures in position.

Materials and equipment

• Cement, sand, aggregate and water for the entire pour plus 5%. Calculate with the slab material calculation.
• Mixer and a standby, two or more needle vibrators, a lift or ramp, gauge boxes, buckets.
• Cube moulds cleaned and oiled.
• Lighting if the pour may run late; polythene in case of rain.
• Enough labour for continuous work.

During the pour

1. Start from one end (usually the far end) and work towards the access point.
2. Pour continuously — avoid interruptions that create cold joints. If a stop is unavoidable, form a construction joint where the engineer specifies.
3. Measure every batch with gauge boxes and measured water. See water-cement ratio.
4. Do not drop concrete from height — it segregates.
5. Vibrate thoroughly, especially around beams, column junctions and congested steel. Do not use the vibrator to move concrete sideways.
6. Keep checking cover — workers walking on steel can push bars down.
7. Level and finish with screed boards; float at the right time.
8. Take cube samples as per specification for 7- and 28-day tests.

After the pour

• Protect from sun, wind and rain as soon as finishing is done.
• Start curing once the surface can take water; pond with mortar bunds. See curing methods.
• Cure for at least 7 days (OPC) or 10 days (blended); 14 days is common practice.
• No heavy loads — do not stack bricks or cement on a new slab.
• De-shuttering: IS 456 gives minimum stripping times with OPC in normal weather — about 3 days for slab soffits with props left under, and props under slabs spanning up to 4.5 m after 7 days and over 4.5 m after 14 days. Blended cements and cold weather may need longer. Follow your engineer.

Key takeaways

• Inspect formwork, steel, cover and services before pouring.
• Stock all materials and backup equipment for a continuous pour.
• Compact well, avoid extra water, take cube samples.
• Cure properly and remove props only when approved.