What Is a Concrete Set Retarder? Function, Dosage and When to Use It

Sep. 24, 2026

Concrete Admixture Technical Guide · No. 10

A set retarder slows the setting of concrete. A small amount gives you more time to place and finish, which is valuable in hot weather and for long transport.

What a Retarder Does

Concrete sets when the cement reacts with water — a process called hydration. A retarder slows this reaction.

The result:

Effect	Benefit
Concrete Stays Workable Longer	More time to mix, move and finish
Setting is delayed, not stopped	Work continues on schedule

A retarder does not replace a water reducer. They perform different jobs: a water reducer lets you use less water, while a retarder gives you more time.

When to Use a Retarder

Situation	Why a Retarder Helps
Hot Weather	Heat accelerates setting; the retarder slows it back down
Long Transport	The truck needs time to reach the site
Large Pours	The first concrete must stay workable while the rest is placed, avoiding cold joints
Mass Concrete	Slower setting lowers the peak temperature

Common Retarders

Retarder	Notes
Sodium Gluconate	The most common; typical dose 0.05% to 0.2%
Sugar (sucrose)	Powerful even at very small doses
Citric Acid	Common
Tartaric Acid	Common
Sodium Lignosulfonate	Also a weak water reducer
Certain Phosphates	Specialised applications

Most retarders are used at about 0.05% to 0.3% of cement weight. Always start low and test — a little too much is worse than a little too little.

The Overdose Risk

This is the key warning.

Too much retarder, and the concrete may not set for a long time — in severe cases, it may never set.

Always test the dose rather than guess. Start low and increase slowly.

Retarder + Water Reducer

Retarders are often used together with a polycarboxylate superplasticizer (PCE) water reducer. The water reducer provides strength and flow; the retarder provides time. Together they give workable, strong concrete, even in hot weather.

With flake PCE, dissolve the flake and add the retarder to the same water — a simple tank and stirrer is sufficient.

One note: do not confuse this with a high slump-retention water reducer. That is a different, specialised product with a slow-release design, and it is not the same as a water reducer plus a retarder.

	Set Retarder	High Slump-Retention PCE
Primary Action	Slows the whole hydration reaction	Releases dispersion gradually
Net Effect	Concrete sets later	Concrete stays workable, sets on schedule