Set-retarding admixtures built on sugars, lignosulfonates or hydroxycarboxylic acids slow early cement hydration so the mix stays plastic longer. Contractors call for them on summer pours, long pump runs, mat foundations and decks where each load must blend into the last before it sets. An overdose can hold off set for a day or more, and a separate surface retarder sprayed on fresh concrete is used to expose aggregate.
Put a half dose of retarder in the afternoon loads, the deck crew can't keep up when it's 95 and windy.
Also heard as
- set retarder
- Type B admixture
Do not mix it up with
- Evaporation retarder: An evaporation retarder is sprayed on the surface to slow moisture loss and does not change set time.
Related terms
Accelerator
An admixture that speeds up setting and early strength gain, mostly used in cold weather.
Admixture
A product dosed into a concrete batch, usually by the ounce, to change its flow, set time, air or durability.
Cold joint
An unplanned seam left where fresh concrete was placed against concrete that had already begun to set.
Initial set
The point at which fresh concrete stops being workable and begins to stiffen into a solid.