Can I use silicone oil as a release agent

Silicone oil can serve as a release agent, but only in specific situations and never as a substitute for a physical separating layer. Silicone oil is a non curing liquid, usually polydimethylsiloxane, available in various viscosities. The oil lowers the interfacial tension between mould and casting, making release easier. It remains liquid, however, and therefore does not form a film you can remove afterwards.

It works well as a thinly wiped release layer for plaster, concrete and some waxes in a rigid mould, provided the casting does not need to be painted, glued or coated afterwards. It is also useful as a lubricant when freeing stuck parts and as an additive in technical applications.

It does not work with casting materials that dissolve or absorb the oil, such as warm fats, waxes above roughly 60 degrees Celsius and solvent rich systems. The oil then leaves with the casting. It also does not work as a separating layer with a thickness of its own, because silicone oil provides no mechanical barrier and does not bridge surface imperfections. If you want a genuine intermediate layer, choose a curing silicone or a physical film.

Do not use silicone oil on castings that will be finished afterwards. Residual oil causes craters, poor paint adhesion and visible staining. When casting addition curing silicone, avoid oils of unknown composition and always check for inhibition first.

Take care with food contact as well. Technical grade silicone oil is not automatically suitable for contact with foodstuffs. Grades with such a declaration do exist, but you must verify this explicitly. Never assume that a technical viscosity grade is food safe.

For most applications a wax based release agent, a release spray or a layer of polyvinyl alcohol performs better, because these do leave a thin film and are matched more precisely to the casting material.

Read more: can I apply silicone as a separating layer inside a rigid mould