Moist cure (concrete)
Moist cure keeps fresh concrete surfaces continuously damp for at least 7 days. Dry cure halves 28-day strength and triggers shrinkage cracking. ABCB 4.2 / AS 3600.
Ask Chalkline about this →Moist cure is the post-pour care regime that keeps the fresh concrete surface continuously damp for at least 7 days after pour, allowing the cement to fully hydrate and develop the design strength. Under AS 3600:2018 and ABCB Housing Provisions Standard 2022 Part 4.2, moist cure is the default required cure regime for residential slabs and footings unless an engineered alternative is documented (verified 2026-05-16).
Why moist cure matters:
- Concrete strength develops over the first 28 days through hydration of cement, a chemical reaction that needs water.
- If the surface dries out in the first 7 days, the cement near the surface cannot fully hydrate. The slab is weaker at the surface than at the core.
- A dry-cured slab typically reaches 50-70% of designed 28-day strength. A moist-cured slab reaches 95-100%.
- Dry cure also produces plastic shrinkage cracks as the surface contracts faster than the bulk; these appear within 24 hours and become permanent.
The four moist-cure methods (in order of cost and effectiveness):
| Method | Cost | Notes |
|---|---|---|
| Wet hessian under polyethylene sheet | Low | Lay wet hessian directly on the surface as the slab finishes setting; cover with 200 micron poly to retain moisture. Re-wet daily. The traditional and most reliable method. |
| Curing compound spray | Medium | Chemical that forms a moisture-retaining film over the slab surface; sprayed within 30-60 minutes of finishing. Removed or worn off before tile, screed or other adhered overlay. |
| Curing blanket / thermal blanket | Medium-high | Insulated blanket laid on the slab; retains moisture and (in cool weather) prevents thermal shock. Commercial pours mostly. |
| Pond cure (continuous water film) | High but rare | Slab kept under a shallow water film for the cure period; relevant on flat-roof or balcony slabs already designed to retain water. |
Cure timeline (typical residential slab):
| Time post-pour | Action |
|---|---|
| 0 to 4 hours | Finishing (broom or steel trowel); slab starts to set |
| 4 to 24 hours | Apply cure method (hessian-and-poly, curing compound) |
| Day 2 to 7 | Maintain cure; re-wet hessian daily; check poly intact |
| Day 7 | Remove cure cover; slab has developed sufficient surface strength |
| Day 28 | Full design strength reached |
Common defects:
- “Dry cure”: slab left exposed after pour, hessian forgotten, or curing compound omitted. Result: low strength, shrinkage cracking, surface dusting.
- Hessian dries out by day 3-4; no re-watering. Effectively dry cure beyond that point.
- Polyethylene torn or blown off by wind on day 2; cure interrupted.
- Curing compound on a slab that will get tile or screed; the compound prevents adhesion and must be removed first (often forgotten).
Cold-weather and hot-weather variations:
- Cold weather (below 10°C): cure period extends; consider thermal blankets to keep slab above 5°C. Below 5°C, hydration effectively stops.
- Hot weather (above 30°C): cure starts within 30 minutes of finishing or surface dries; cure-compound sprays are preferred over hessian (which dries too fast).
Also known as: wet cure; concrete cure; 7-day cure.
Category: Materials.
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Last updated: 2026-05-16. Verified: 2026-05-16. Quarterly review for currency.