The right release agent can make or break the success of a molding process. Use too much, and you’ll lose surface detail. Use too little, and the casting will stick to the mold. This guide compares the most common types of release agents and explains when to use each one.
Why use a release agent?
Although silicones are generally self-releasing, there are many situations in which a release agent is essential:
- Silicone on silicone: When pouring silicone into a silicone mold, the new material will otherwise permanently adhere to the existing one
- Reactive casting materials: Polyurethane resins, certain epoxy resins, and polyester resins adhere strongly to silicone molds
- Extend service life: Release agents reduce wear on the mold surface
- Non-silicone molds: Molds made of fiberglass, wood, plaster, metal, or 3D-printed materials always require a release agent
Comparison of Release Agent Types
| Type | base | release film | Attention to detail | Suitable for |
|---|---|---|---|---|
| Wax release agent | Carnauba wax/paraffin wax | Thin, shiny | ★★★★☆ | FRP molds, resin, concrete |
| PVA release agent | Polyvinyl alcohol/water | Water-soluble film | ★★★☆☆ | Resin on fiberglass, epoxy on epoxy |
| silicone spray | Silicone/solvent-based | Paper-thin | ★★★★★ | Quick demolding, universal |
| PTFE Spray | Teflon dispersion | Dry film | ★★★★☆ | Abrasive materials, high temperature |
| Vaseline/grease | Petroleum | Thick, oily | ★★☆☆☆ | Large molds, concrete, plaster |
| Semi-permanent | Reactive silicone | Bound layer | ★★★★★ | Mass production, 50+ demoldings |
Wax release agent
The classic choice. Carnauba wax is applied in a thin layer, dries to a hard, glossy film, and ensures clean demolding. For best results: Apply 3–5 coats, polishing each coat. Suitable for fiberglass lamination, resin casting in fiberglass molds, and concrete mold making.
Disadvantage: Time-consuming (multiple coats); wax residue on the casting can interfere with the paint finish.
PVA release agent (polyvinyl alcohol)
The Safe Choice. PVA release agent forms a water-soluble film that can be easily washed off after demolding. It is often used in combination with wax: first wax as a base coat, then PVA as a safety layer.
Highly recommended when pouring epoxy resin into an epoxy mold —without PVA, there is a risk of a permanent bond forming.
Silicone spray as a release agent
The Fast One. Silicone spray (e.g., ACHEM SG-1001) provides immediate release with minimal application. Ideal for rapid production runs and prototyping. The ultra-thin film has virtually no effect on surface details.
Warning: Silicone spray can make subsequent painting impossible (causing pitting). In areas where painting is taking place, use silicone-free release agents.
Semi-permanent release agents
The Professional. Reactive release agents that form a permanent, bonded release layer on the mold surface. A single application lasts for 20–50+ demoldings. Significantly more efficient than wax or spray in mass production.
→ Renlease semi-permanent release agents
Which release agent should be used for which casting material?
| Casting material | In a silicone mold | Made of epoxy/fiberglass | In metal form |
|---|---|---|---|
| epoxy resin | None or silicone spray | Wax + PVA | Wax or semi-permanent |
| polyurethane resin | Silicone spray recommended | Wax + PVA | Wax or semi-permanent |
| Silicone on silicone | Vaseline + dish soap | – | – |
| Plaster / Concrete | Not necessary | Vaseline or wax | Oil or wax |
| Wax (candles) | Not necessary | silicone spray | silicone spray |
| Tin / Low-melting-point metal | None (heat-resistant Si) | – | Graphite or BN |
Practical Tips
- Less is more: A release agent film that is too thick fills in fine details and compromises surface quality
- Adjusting to new molds: The first 2–3 castings from a new silicone mold often require more release agent than subsequent ones
- Silicone on silicone: The only reliable method is to apply a barrier layer of petroleum jelly mixed with a drop of dish soap (for better wetting)
- Mass production: Invest in semi-permanent release agents—the time savings pay off starting at 20 parts
