How to Fill Cracks and Gaps in a Resin Collectible

Cracks in resin collectibles range from hairline stress fractures to wide gaps from breaks or manufacturing defects. Different crack types need different approaches, but all are fixable at home.

Diagnosing the Crack

• Hairline crack — superficial, doesn't go all the way through. Often caused by thermal stress or impact without breaking
• Stress fracture — deeper crack that may widen over time if not stabilised
• Gap at a join line — common at assembly points or mould seams on cheaper pieces
• Impact chip with missing material — requires gap-filling rather than just crack-filling

Method 1 — Super Glue for Hairline Cracks

For very fine hairline cracks with no missing material: flow a tiny amount of thin cyanoacrylate (super glue) into the crack and let capillary action draw it in. It will wick into the crack and stabilise it. Wipe any excess immediately with a dry cotton bud. Allow to cure 24 hours. Sand flush with 800–1000 grit if necessary, then repaint.

Method 2 — UV-Cure Resin for Gaps Up to 1–2 mm

UV-cure resin has an excellent working time — it stays liquid until you cure it with a UV lamp. Apply with a fine applicator tip or toothpick, shape to slightly overfill the gap, cure with a UV lamp for 60 seconds, then sand flush progressively (400 → 800 → 1000 grit wet). Produces a hard, sandable, paintable surface.

Method 3 — Epoxy Putty for Larger Gaps

Two-part epoxy putty (Milliput Standard, Milliput Superfine) is the best choice for gaps wider than 2 mm, missing chunks, or areas that need sculpting. Mix equal parts, work within the 30–60 minute open time, sculpt with silicone-tipped tools dampened with water. Superfine grade sands to an almost seamless finish.

Sanding the Repair

Work through grits progressively: start where you need to (180 for large fills, 400 for UV resin), and always finish at 1000 or higher before priming. Wet sanding (using a little water on the paper) gives a smoother result and extends the life of the paper.

Priming Before Repainting

Always prime the filled area — even a perfectly smooth fill looks different from the surrounding painted surface under paint without primer. Two thin coats of grey acrylic primer, allowed to dry fully, is sufficient. Sand lightly between coats for the best surface.