ASTM C309
Standard Specification for Liquid Membrane-Forming Compounds for Curing Concrete
Spray-applied curing compounds — the products that form a temporary film to hold moisture in fresh concrete instead of wet curing it.
Who needs it
Flatwork and paving contractors, curing-compound manufacturers, inspectors, and specifiers writing a curing requirement.
What the test involves
It sorts curing compounds by type, including clear, clear with a fugitive dye that shows coverage during application, and white-pigmented products that reflect heat on pavements, and by the resin class used. The core requirement is that the film limit moisture loss from the concrete during the critical early curing period. Products qualifying under it are intended to disappear or degrade over time rather than serve as a permanent coating.
Common misconceptions
- A curing compound is not a sealer. It is designed to break down, and treating it as long-term protection leaves the slab unprotected.
- Coverage rate is the whole ballgame. A compound applied thinner than its rated rate does not cure at a reduced level, it simply fails to form a continuous film.
- Curing compound left on a slab that will later receive coatings, stains, tile, or flooring is a bond-failure risk, which is why it is often prohibited on floors scheduled for finishes.
Official source
We summarize scope and purpose only. The full text belongs to the issuing body — read it at the official source. ASTM International