A poorly chosen release agent is noticeable: dark stains on the visible surface, surface blisters, difficulty cleaning the mold, and, in the long run, accelerated deterioration of the formwork. The difference between site and precast release agents is not marketing — it responds to different chemistries and finishing requirements.
The four chemical families
Pure mineral oil. Low cost, easy application, but leaves a greasy film and stains the visible concrete. Suitable for hidden formwork in civil works.
Oil-in-water emulsion. Diluted in water, low flammability, good environmental performance. Correct finish in situ. Requires frequent reapplication.
Synthetic ester. Slightly reacts with cement paste creating a layer of calcium soap that facilitates release without staining. Smooth finish, ideal for visible concrete.
Reactive chemical. Controlled reaction with cement that repels water and leaves a uniform finish. Preferred category in high-demand precast.
Site vs precast
The site release agent works with successive formworks, many cycles, exposure to weather conditions, and variable cleaning. Ease of application and tolerance to overdosing are prioritized.
The precast release agent works with high repeatability molds and very strict surface finishing requirements (visible faces, decorative textures). Cleanliness of the finish, absence of stains, and long-term protection of the metal or polyurethane mold are prioritized.
The Quimicasur range
Desmolnet — water-dilutable concrete release agent. Designed for in situ work: wooden, metal, and mixed formworks. Good mold protection and easy cleaning.
Desmolnet E — pure release agent (active substance 100%) for metal formworks where a fine finish is sought without intermediate dilutions.
Desmolnet M — specific for decorative molds and precast. Opaque white liquid, insoluble in water, designed to preserve the texture and reliefs of the mold without staining the concrete.
Application and dosing
Fine and uniform spraying, avoiding puddles. Excess causes blisters (air bubbles trapped on the visible face). Waiting time between application and concreting: 30 min to 2 h depending on the product.
In summer, slightly reduce the dose: the oil evaporates faster and the film becomes thinner. In winter with cold formwork, increase the dose to ensure continuity of the film.
Mold care
A good release agent extends the useful life of the mold. But it does not replace periodic cleaning: accumulated paste residues generate defects on any visible concrete. Every 5-10 cycles, gentle mechanical cleaning and generous reapplication.