The basic task of a form release agent is to permit clean release of the form from hardened concrete during stripping. Several types of form release agents are available, some better suited to a particular form material than others. Five basic types are described in this article: petroleum oils; emulsions; non-reactive coatings with volatile solvent; waxes; and chemically active agents containing fatty acids.
Light-bodied (low viscosity) petroleum oils are available from major oil companies. Petroleum oils provide good form release and if properly applied will produce uniform concrete color. In a plain oil with wetting agent, surface activating agents are added to plain oils to dissipate the oil so it will not bead up on the form and produce bugholes.
Emulsions consist of a water phase, a water-insoluble phase and an emulsifier which suspends one phase in the other.
NON-REACTIVE COATINGS WITH VOLATILE SOLVENT
These form release agents consist of a volatile solvent derived from petroleum combined with one or more active ingredients, such as waxes, silicones, synthetic resins and water-insoluble soaps. The solvent evaporates, and the active ingredients are left behind on the form surface.
Though rarely used today, waxes have excellent release characteristics.
CHEMICALLY ACTIVE AGENTS CONTAINING FATTY ACIDS
A majority of the proprietary form release agents on the market today are chemically active, in the sense that they react with the free lime in concrete. The reactive component is usually fatty acid in the form of animal fat or vegetable oil. These weak acids react slowly with the alkalis in concrete to produce water-insoluble soaps. This process is called saponification.