Curing compound (concrete)
Curing compound is the liquid film sprayed on fresh concrete to retain moisture for hydration. Spec'd to AS 3799. Cheaper than wet hessian; compatible-check needed.
Ask Chalkline about this →A curing compound is a proprietary liquid sprayed or rolled onto a freshly finished concrete surface that dries to form a moisture-retentive film, allowing the concrete to hydrate and cure without ongoing wetting. It is the standard Australian residential alternative to wet hessian curing or plastic-blanket curing, which require regular re-wetting and are inconvenient on tight sites or in hot weather. Curing compounds are specified to AS 3799:1998 and applied per the concretor’s normal site practice (verified 2026-05-16).
Why curing matters:
| Without curing | With curing |
|---|---|
| Surface dries before hydration completes | Hydration proceeds for the full 7-28 days |
| Top layer is weak, dusty, scales | Top layer reaches design strength |
| Reduced wear life | Full wear life |
| Surface cracking (plastic shrinkage cracks at hours; drying-shrinkage cracks at days) | Suppressed early cracking |
| In-service moisture absorption is higher | Lower; finished concrete is more impermeable |
A residential slab that is not cured loses up to 30% of its design compressive strength in the top 20 mm of the slab. This is the layer most exposed to wear, salt attack, and freeze-thaw cycling, so the loss is concentrated where it hurts most.
Curing compound types:
| Type | Composition | Use |
|---|---|---|
| Wax-based (Type W) | Petroleum wax in solvent or water emulsion | Most common residential; opaque/white when cured |
| Resin-based (Type R) | Acrylic or other resin film | Some commercial; transparent or coloured |
| Sodium silicate | Soluble silicate; chemical cure | Floor-hardener combinations |
| Hybrid | Resin + wax + chemical | Premium driveways and floors |
(All current types are specified against AS 3799 performance bands.)
Application:
- Timing: apply as soon as the surface is just dry to the touch and any bleed water has dissipated. Typically immediately after final brooming/finishing.
- Method: low-pressure spray (garden-pump sprayer common on residential), back-roll for an even film.
- Coverage: typically 3-5 m² per litre depending on product. Manufacturer spec is authoritative.
- Direction: apply two thin coats at right angles to avoid streaking, rather than one thick coat.
- Avoid trafficking: 4-12 hours before light foot traffic depending on product.
Compatibility with subsequent finishes:
The curing compound’s film must be removed or chemically compatible with any subsequent treatment of the slab. Critical compatibility checks:
| Subsequent finish | Compatibility risk |
|---|---|
| Vinyl, lino, glue-down flooring | Adhesive bond can fail on residual curing compound; mechanical or chemical removal needed |
| Carpet (direct-stick or staple) | Less critical; surface needs to be clean and dry |
| Tiles (adhesive) | Acrylic compounds compatible with tile adhesives; wax compounds incompatible, must be removed |
| Floor paint, epoxy | Most curing compounds incompatible with epoxy or coloured floor finishes; mechanical removal needed |
| Polished concrete | Wax compounds incompatible with grinding/polishing |
| Stamped concrete colour wash | Most compounds prevent colour penetration; do not use |
A residential project must align the curing compound choice with the final floor covering at the design stage. The most common defect is a wax-based curing compound applied to a slab that the builder later decides to polish or epoxy-coat.
AS 3600:2018 curing duration:
| Concrete grade | Curing duration |
|---|---|
| N20-N25 (typical residential slab) | 7 days |
| N32-N40 (heavier residential or commercial) | 7-14 days |
| N50+ (specialised) | 14-21 days |
Curing compound is rated to provide moisture retention for the relevant duration; manufacturer documentation should confirm AS 3799 compliance for the specified period.
Common defects:
- Insufficient coverage: streaks or thin patches. The slab cures unevenly; some areas weak.
- Late application: bleed water trapped under the compound; surface laitance forms.
- Wrong compound for subsequent finish: most common defect; finish fails to adhere; replacement is expensive.
- Trafficking too early: footprints in the cured film; weak spots.
- No compound applied at all: builder assumed “the slab will be fine”; surface scaling within months.
Also known as: concrete sealer (loose usage; sealer is technically different); curing membrane; spray curing; AS 3799 compound.
Category: Materials.
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Last updated: 2026-05-16. Verified: 2026-05-16. Quarterly review for currency.