Technical Questions

ACI Committees, Membership, and Staff have answered common questions on a variety of concrete related topics.

Form release agents

Q. I need to select a form release agent for a new project requiring an architectural finish. Can you provide information on different types of form release agents and recommendations for using them? Does ACI have a publication on form release agents I could use as a reference?


A. Form release agents ease formwork removal, extending the useful life of a form and improving the smoothness and texture of concrete surfaces. Two main types are available: barrier and chemically active.

Barrier-type agents (examples include diesel oil, wax, and silicone) create a barrier between the form and the concrete. These are not recommended for architectural concrete, because they can cause stains, surface air voids, and problems with form removal in very cold or very hot weather; they also may prevent subsequent adhesion of coatings to the hardened concrete. While diesel oil was once commonly used, it’s now prohibited because the associated volatile organic content (VOC) emissions contribute to smog. (Note: In the United States, form release agents have to meet federal VOC limits of 450 g/L [3.8 lb/gal.] and may have to meet more restrictive limits of 250 g/L [2.2 lb/gal.] in some states.)

Chemically active form release agents (certain types of fatty acids) react with calcium ions in the cement paste to produce a soap that prevents concrete from bonding to the formwork. Based on the reactivity, they are divided into buffered (partially) reactive and fully reactive. Buffered agents produce an improved soap film that helps remove entrapped air and may promote better flow of a thin skin of cement paste at the surface of the form. Fully reactive agents can provide a good basic soap film that, depending on the brand, works well in most cases. Because chemically active form release agents produce fewer bugholes, stains, and surface irregularities than barrier type of form release agents, they are commonly used for architectural concrete.

For more information on this topic refer to ACI 347R “Guide to Formwork for Concrete”, ACI 303R “303R-12 Guide to Cast-in-Place Architectural Concrete Practice”, and ACI 533R “Guide for Precast Concrete Wall Panels”.


References: ACI 347R-14; ACI 303R-12; ACI 533R-11

Topics in Concrete: Architectural Concrete; Formwork

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