# Post-Cast Strip Calculator

Enter strip length, width, slab thickness and waterstop size to get concrete volume plus waterstop length and weight.

- Page: https://jianzhujisuan.com/en/post-cast-strip
- Category: Concrete (https://jianzhujisuan.com/en/c/concrete)
- Chinese version: https://jianzhujisuan.com/zh/post-cast-strip.md
- Data checked: 2026-10-25

## Quick result

With the default inputs (Total strip length 30 m, Strip width 0.8 m, Slab or wall thickness 0.2 m, Waterstop width 300 mm, Waterstop thickness 3 mm, Number of waterstop lines 2 courses, Waste allowance 3%): **Concrete volume 4.80 m³**

## Inputs

| Parameter | Type | Default | Unit | Note |
|---|---|---|---|---|
| Total strip length | number | 30 | m | Sum of all strip lengths |
| Strip width | number | 0.8 | m | Typically 700-1000 mm |
| Slab or wall thickness | number | 0.2 | m |  |
| Waterstop width | number | 300 | mm | Usually 300 mm; 200 or 400 also common |
| Waterstop thickness | number | 3 | mm | Typically 2-4 mm |
| Number of waterstop lines | number | 2 | courses | One each side of the strip, so 2 normally |
| Waste allowance | number | 3 | % |  |

## Formula

- **Concrete volume**: V = total length × width × thickness
- **Waterstop length**: L = total length × number of lines
- **Weight per metre**: g = width(m) × thickness(m) × 7850　(kg/m)
- **Total weight**: W = L × g × (1 + waste %)

## Worked example

30 m of strip, 0.8 m wide, 0.2 m thick, 300×3 waterstop both sides: 4.80 m³ concrete, 60 m of plate at 7.07 kg/m, 437 kg including 3% waste.

## Questions

### Why must the waterstop flange face the water side?

The bent flange goes toward the water side — outward for basement walls, downward for base slabs. Seepage then has to travel around a lip that is pressed tighter as pressure rises. Installed backwards it becomes a channel and cannot be corrected after casting. Flanges are typically 30-50 mm, welded both sides.

### When can the post-cast strip be poured?

Settlement strips wait until the main structure tops out and settlement stabilises (usually at least 60 days). Shrinkage strips are specified at 42 days minimum, often 60 in practice. Before pouring: clear debris, scabble the interface, derust the bars, use one grade higher with an expansive agent, and cure for at least 14 days.

### Waterstop plate or swelling strip?

The steel plate lengthens the seepage path and is welded, so it is durable and reliable for higher pressure — basement slabs and walls. Swelling strips compress the gap by absorbing water; easy to install but not for high pressure, and their swell capacity fades with long immersion. Using both in critical locations is common.

## Related tools

- [Concrete Volume Calculator](https://jianzhujisuan.com/en/concrete-volume): Enter length, width and thickness to get the concrete volume you need and how many truck loads that is.
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- [Concrete Mix Design Calculator](https://jianzhujisuan.com/en/concrete-mix-ratio): Work out cement, sand, gravel and water per cubic metre from the target grade and water-cement ratio.
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- [Concrete Pour Sequencing Calculator](https://jianzhujisuan.com/en/concrete-pour-plan): Divide a slab into strips and get the volume, truck count and duration for each pour.
- [Concrete Strength Converter](https://jianzhujisuan.com/en/concrete-strength-convert): Convert between grade, MPa, psi and kgf/cm², with cube-to-cylinder correction.

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