Casting resin is versatile, but project success requires knowing what materials are not compatible with the curing process or the final product’s integrity. For manufacturers, avoiding incompatible materials prevents costly waste, defects, and product failure.
The Fundamental Rule: Moisture is the Enemy
Casting resins (especially epoxies and polyurethanes) are highly sensitive to moisture during curing, which can cause: incomplete cure/tackiness, excessive bubbles/cloudiness, and surface defects.
Materials to Avoid Due to Moisture Content:
- Fresh Flowers, Leaves, and Greenery: Must be thoroughly dried and sealed first; otherwise, they will cause bubbling and eventual rotting inside the resin.
- “Wet” Organic Materials: Includes fresh fruit, vegetables, and undried wood (green wood).
- Unsealed Porous Materials: Materials like paper, concrete, or raw wood must be meticulously dried and sealed(e.g., with a thin coat of resin or compatible sealer) to prevent moisture outgassing and absorption.
Materials That React Negatively or Degrade
| Category | Why to Avoid or Use Caution | Actionable Advice |
| Low Surface Energy Plastics | Resin will not stick due to their inert, non-stick properties. Examples: Polyethylene (PE), Polypropylene (PP), Silicone, Teflon (PTFE). | Test unknown plastics first. Silicone is only for molds, not embedding. |
| Unsealed Paper and Photos | Contains moisture, can become translucent, or discolors when exposed directly to liquid resin. | Seal porous items (paper, photos) with a thin layer of resin, Mod Podge, or spray sealant beforehand. |
| Volatile/Reactive Inclusions | Materials that off-gas during the resin’s exothermic cure (causing large bubbles or cracks) or inhibit the cure. | Only use pigments and dyes specifically formulated for resin. Avoid water-based paints. |
| Air-Filled/Hollow Items | Trapped air pockets (e.g., hollow beads, unsealed pinecones) can expand thermally during the exothermic cure, causing them to crack, float, or release bubbles. | For hollow items, drill venting holesor fill them with resin prior to the main pour. |
Incure: Your Partner in Precision Casting
Incure provides high-performance casting resins and the critical technical knowledge to ensure successful, defect-free projects:
- Formulated for Predictable Performance: Our resins are designed to minimize reactivity issues with compatible inclusions.
- Expert Technical Guidance: We offer tailored advice on material compatibility, drying/sealing preparation techniques, and troubleshooting issues like stickiness or cloudiness related to material interactions.
Actionable Advice for Casting Inclusions:
- Always Dry Thoroughly: Organic material must be bone-dry before embedding.
- Seal Porous Items: Apply a thin, compatible sealant layer to prevent air bubbles and discoloration.
- Perform Small Tests: If unsure about a material’s compatibility, always do a small test casting first.