How to Fix and Prevent Bubbling in Resin Miniature Casts

Quick answer

Most surface bubbles in resin casts are pinholes or blowholes that you can fill with thin CA glue or epoxy putty after washing and trimming. Large internal voids, short casts, or bubbles on thin detail edges usually mean the part is structurally compromised—stop and request a replacement rather than trying to rebuild it.

Identify the bubble type before you touch the model

Resin casting problems show up in three main forms: pinholes (tiny surface craters), blowholes (larger round voids, often clustered), and short casts (missing or rounded-off detail). Pinholes are the most common and the easiest to fix. Blowholes can be filled if they are shallow, but deep ones may hide more voids underneath. Short casts are a molding failure—no amount of filler will restore missing geometry.

Clean and inspect before any repair

Wash resin parts in warm water with a mild dish soap and a soft toothbrush to remove mold release agent. Let them dry completely. Under good light, mark every bubble with a fine-tip marker so you do not lose track during sanding. This step also reveals whether the bubbles are only on the surface or connect to deeper cavities.

Repair pinholes and shallow blowholes

For pinholes, apply thin CA glue with a needle applicator and let it cure, then sand flush with 600–1000 grit wet sandpaper. For slightly larger blowholes, use a two-part epoxy putty. Press it into the void with a silicone shaper, let it cure, then sand and reshape. If the bubble sits on a flat surface, a tiny dot of UV resin can also work, but cure it fully before sanding.

When heat can help—and when it cannot

A hair dryer on low or a cup of hot (not boiling) water can soften thin resin and let you push a warped or slightly short edge back into shape. This only works for minor short casts on thin parts, not for missing chunks. Overheating will distort detail permanently, so keep the heat gentle and move constantly.

Prevent new bubbles during cleanup and assembly

After repair, avoid trapping air when you prime or glue. Use thin layers of primer and press parts together slowly. When you pin a joint, drill a slightly larger hole than the pin so trapped air can escape. Store resin parts in a dust-free box; dust in a pinhole makes it look worse after painting.

Stop and replace if the defect is structural

If a bubble sits on a thin weapon barrel, a facial feature, or a load-bearing joint, filling it will not restore strength. In those cases, the safest option is to contact the seller for a replacement or return. For secondhand resin, remember that sales are often final and sold as-is, so inspect immediately upon arrival and before you cut or glue anything.

Diagnosis: match the symptom to the fix

• Tiny surface craters (pinholes): Caused by small air bubbles trapped against the mold surface during casting. Fill with thin CA glue, cure, and wet-sand flush. Repairable with basic supplies.
• Larger round voids (blowholes): Caused by air pockets that did not escape before the resin set. If shallow, fill with epoxy putty and reshape. If deep or on a thin edge, the part is weak. Fill only if the void is shallow and not load-bearing.
• Missing or rounded detail (short cast): Caused by incomplete mold filling, often from cold resin or insufficient pressure. No filler can restore missing geometry. Stop and request a replacement or return.

Products that help with resin repairs

• Citadel: Air Mournfang Brown (24Ml): Citadel Air Mournfang Brown is a 24ml acrylic paint formulated for airbrushes, designed for basecoating and shading miniatures. Thin airbrush paint like this flows into small pinholes without clogging detail, making it a good choice for checking your repair work before priming.
• Necrons: Skorpekh Destroyers: Necrons: Skorpekh Destroyers contains 4 push-fit plastic Citadel Miniatures and is an Elites choice for Necron armies, fielded in squads of up to 6. If your resin repair is for a Necron force, these plastic push-fit models can replace a badly damaged resin piece without needing filler or structural work.