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Post-Cast Strip Calculator

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

Quick answer

With the default inputs: Total strip length 30 · Strip width 0.8 · Slab or wall thickness 0.2 etc.Concrete volume 4.80 m³

Edit the inputs below to recalculate.
Length LDepth HWidth W
Volume is design width (usually 800-1000 mm) times slab depth; the waterstop plate is separate. Formwork left in place on both faces still counts.

Inputs

Sum of all strip lengths
Typically 700-1000 mm
Usually 300 mm; 200 or 400 also common
Typically 2-4 mm
courses
One each side of the strip, so 2 normally
%

Result

Concrete volume
4.80m³
Waterstop total length60.0m
Waterstop weight per metre7.06kg/m
Waterstop weight (incl. waste)436.6kg
Waterstop area18.0m²
Formed area12.0m²

Covers the strip itself only, excluding interface scabbling, cleaning, rebar derusting and the premium for shrinkage-compensating concrete. Post-cast strips normally use one grade higher plus an expansive admixture.

Formula

Concrete volumeV = total length × width × thickness
Waterstop lengthL = total length × number of lines
Weight per metreg = width(m) × thickness(m) × 7850　(kg/m)
Total weightW = L × g × (1 + waste %)
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.

How to work it out

  1. Concrete volume = total strip length × width × slab or wall thickness, as a net figure.
  2. Post-cast strip concrete is normally one grade above the adjacent work and shrinkage-compensating, with its own mix design.
  3. Waterstop length = strip length × number of runs. Typically one in a base slab, one or two in walls and roof slabs.
  4. Steel weight per metre = width (m) × thickness (m) × 7,850; a 300×3 strip is 7.065 kg/m.
  5. Add 3% waste: corners, lap welds and junctions with columns and walls all require cut pieces.

Where it goes wrong

Material and cost

Strip concrete costs 60-120 per m³ more than normal (higher grade plus expansive agent). A 300×3 waterstop is about 12-18 per metre fabricated, plus 15-25 per metre to weld and fix. The formwork and props must stay in place throughout, and that cost is routinely left out of the estimate.

On site

Basis

FAQ

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.

Cite this page

Use this format in reports, method statements or coursework. The link is permanent.

Building Calculator. Post-Cast Strip Calculator. 2026-10-25. https://jianzhujisuan.com/en/post-cast-strip

Results are estimating aids only and are not a design basis. Construction and final accounts must follow the drawings, the applicable standards and an approved method statement. Anything affecting structural safety, shoring or falsework must be checked by a suitably qualified engineer.