Not every member can be poured in one go — a long day, a breakdown or a rain shower can stop a pour. Where the joint ends up, and how it is prepared, decides whether it is a harmless line or a weak plane.
Planned vs Cold Joints
| Construction joint | Cold joint | |
|---|---|---|
| Planned? | Yes | No — concrete set before the next batch |
| Location | Chosen for low stress | Wherever the delay happened |
| Preparation | Proper surface treatment | Often none |
| Risk | Low if done right | Weak plane, leak path |
Where IS 456 Puts Them
| Member | Location |
|---|---|
| Slabs and beams | Middle third of the span |
| Beam meeting a girder in that zone | Offset by about twice the beam width |
| Columns | Just below the beam soffit; top of floor slab |
| Walls and sumps | As designed, with waterstops for water-retaining work |
Joints are formed vertical in slabs and beams, with a stop-end board, not left as a sloping heap of concrete.
Preparing the Joint
- Remove laitance — the weak, milky surface layer.
- Roughen to expose aggregate, by wire brushing while green or chipping once hard.
- Clean off dust and debris.
- Wet the surface, without leaving standing water.
- Apply cement slurry or a bonding agent immediately before the new pour.
- Compact the new concrete well against the joint.
Avoiding Cold Joints
- Have materials, labour, vibrators and a standby for the whole pour.
- In hot weather, use a retarder and pour early.
- Pour in layers that are covered before the previous one sets.
- Plan where to stop if you must.
The Short Version
Plan joints in low-stress places, form them vertical, prepare them properly, and avoid cold joints by having everything ready for a continuous pour.
