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Inspection & Familiarization
Resin Kit Defects & Fixes

Pour Stubs

Most parts will have at least one "pour-stub" where the activated resin was poured into the mold, slightly over-filling it.

The stubs will need to be removed when you prep the parts.


Bubbles are probably the most-common casting artifact in resin kits.

Positive bubble

Most likely, when the mold was made, some air was trapped around the master, making small negative bubbles in the wall of the mold. When the casting is made, resin enters these voids in the mold and makes a positive bubble on the model part.

FIX: Use a hobby knife or file to remove them.

Negative bubble

If the resin has air in it, or is poured too quickly, air can become trapped in the piece. If it happens at the surface, you'll have a negative bubble.

FIX: Fill them with putty or gel-type superglue and sand or file smooth.

Internal bubble

Aka "resin sponge" - If the resin has lots of air in it from mixing, when the casting is poured that air will rise inside the mold. If it can't escape through a stub, it could simply become trapped inside the part. The part may appear solid from the outside, but when viewed back-lit the internally-trapped bubbles are obvious. This area will be quite weak because of the bubbles, prone to punctures or crushing.

FIX: Carefully puncture the bubble(s) and squeeze some gap-filling or gel-type superglue inside, or use a quick-setting epoxy.

If the part has a flat surface, as in the image, cap it with thin sheet styrene superglued to the piece.

Worst-case: cut away the spongey section and rebuild it with epoxy putty or request a replacement piece.

Casting Seams

If the mold halves don't fit together precisely - whether due to being poorly made to begin with or due to age -  there'll be a seam visible.

FIX: Sand and/or file the seam. It may be necessary to putty over the seam before filing.

Incomplete Molding

If resin doesn't make it all the way into part of the mold, and the maker has poor QC, you may find that you only have part of a part.

FIX: Build out the missing section with putty or spare parts, or request a replacement.

Mold Deformation

If the mold has too-thin a wall, it may sag under its own weight, deforming the part inside. Or perhaps someone bumped the mold or leaned something against it.

FIX: You may be able to heat and reshape the part if the deformation isn't too severe.

Surface Irregularities

For whatever reason, sometime a part just has an irregularity in the surface.

FIX: Either fill them or file them.




The Model Citizen's "Sprue U" pages are �2000-2004 Roger Sorensen
last updated 04 December, 2007