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What is a concrete release agent? Qilin takes you on an in-depth look at this invisible guardian of the construction industry.

Publish Time: 2025-08-15

On construction sites, the precise shaping and surface finish of concrete components directly impact the quality and aesthetics of the building. Behind this, a seemingly inconspicuous yet crucial material—concrete release agent—plays a crucial role. Acting as a lubricant and protective film between the mold and the concrete, it ensures smooth concrete release from the mold while protecting the perfect shape of the building structure. This article will demystify this building material from five perspectives: its definition, mechanism of action, classification, selection criteria, and future trends.

1. Release Agent: The Invisible Driver of Concrete Forming

Concrete release agent is a functional material applied to the inner surface of the formwork after concrete is poured. Its core function is to physically or chemically form a barrier between the formwork and the concrete surface, reducing the adhesion between the two. This allows the concrete to be easily removed from the formwork after hardening, while maintaining a smooth surface. This process not only avoids damage to the formwork caused by traditional demolding methods (such as hammering and prying), but also significantly improves the yield rate and surface quality of concrete components. For example, in bridge construction, the lack of a release agent during the demolding of large precast beams can lead to honeycombing, roughness, and even fractures on the beam surface due to adhesion between the concrete and the steel formwork. High-quality release agents, however, ensure a mirror-like surface, meeting high-standard engineering requirements.

2. Mechanism of Action: Four mechanisms address demolding challenges

The mechanisms of action of release agents can be categorized into four categories:

① Physical Lubrication

Oil-based release agents (such as mineral oil and vegetable oil) lubricate the formwork surface, reducing friction between the concrete and the formwork, facilitating a smoother demolding process. For example, petroleum-based lubricants form a low-viscosity film upon application, reducing the cohesion of the concrete and allowing the formwork to be easily removed under external force.

② Film-forming Isolation

Materials such as emulsified oil and alkali-resistant paint quickly dry and form a film on the formwork surface, creating a physical barrier. For example, emulsified wax release agents, applied through a spray process, form a uniform film on the steel formwork surface that is water-resistant and reusable. The domestically developed BT-20 release agent can even be demolded over 40 times.

③ Chemical Action

Fatty acid release agents (such as stearic acid) react with free calcium hydroxide in concrete to form a water-insoluble fatty acid salt barrier. These release agents are non-toxic and non-polluting, but the application process must be strictly controlled to prevent powdering of the concrete surface.

④ Comprehensive Protection

Resin release agents (such as epoxy resins) combine lubrication, isolation, and rust prevention through a complex chemical synthesis process. While they offer excellent release performance, they are relatively expensive to produce and are primarily used in projects requiring extremely high concrete surface quality.

3. Classification and Selection: Adaptability is Key

Based on their composition and intended use, release agents can be categorized into the following types. When selecting a release agent, consider the formwork material, construction environment, and concrete properties:

Types	Element	Applicable Scenarios	Advantages	limitation
Oil-based release agent	Mineral oil, vegetable oil	Steel formwork, low-temperature environments	Strong lubricity and excellent rust prevention	Easy to pollute the concrete surface, poor environmental protection
Water-based release agent	Water-based polymer	Wooden formwork, projects with high environmental requirements	Non-toxic, odorless, and easy to clean	Weak heat resistance, easy to fail at high temperature
Emulsion-based release agent	Emulsified wax, synthetic resin	Usable for both steel and wooden formwork	Excellent overall performance and convenient application	Storage stability needs to be strictly controlled
Paint-based release agent	Alkali-resistant resin, hydrophobic groups	High-frequency formwork (e.g., precast component plants)	Wear-resistant and water-resistant, suitable for multiple recycling	High cost and complex production process
Silicone-based release agent	Methyl silicone resin	Precision components, mirror-finish concrete	Extremely efficient demolding and near-mirror-like surface quality	Expensive, only used in high-end projects

Selection Example:

When constructing in cold regions, choose a frost-resistant release agent (such as a linoleic steel formwork release agent) to prevent brittle cracking caused by low temperatures.

For steam-cured concrete components (80-90°C), GFC-90 resin-based release agent can withstand high temperatures without failure.

For wooden formwork, a penetrating release agent is recommended to seal gaps, prevent cracking, and extend the formwork's service life.

4. Construction Key Points: Details Determine Success

① Formwork Pretreatment

Before use, thoroughly clean the formwork surface to remove oil, rust, and dust. Steel formwork can be sanded, while wooden formwork should be soaked in a chemical cleaner to ensure a good bond between the release agent and the formwork.

② Application Process

Spraying: Suitable for large, flat forms, ensuring high efficiency and uniform film coverage;

Brushing: Suitable for special-shaped forms or detailed areas, ensuring complete coverage;

Roller coating: Commonly used for small and medium-sized forms, balancing efficiency and uniformity.

Note: Increase the application amount for the first application, especially focusing on corners.

③ Dosage Control

Apply 80-150 grams of release agent per square meter of formwork surface. Excessive application will cause runoff and affect release effectiveness, while insufficient application will prevent a complete barrier film from forming.

④ Storage and Safety

Release agent should be stored in a cool, dry place, away from direct sunlight and high temperatures. Applicators should wear protective gloves, masks, and goggles to prevent skin contact and inhalation of volatile fumes.

Small Materials, Large Mass

Although concrete release agents account for less than 1% of construction costs, they directly impact the quality, efficiency, and sustainability of projects. From bridges to high-rise buildings, from landscape architecture to municipal infrastructure, this "invisible guardian" is reshaping the future of the construction industry with the power of technology. As the Qilin brand advocates: "Achieve perfection with details and define standards with innovation." Choosing a suitable release agent is not only a technical consideration, but also a commitment to building quality.