Common Casting Defects and How to Fix Them
Most casting defects look mysterious the first time you see them and completely obvious once you know what to check. Here's a field guide to the ones we hear about most.
Porosity (small voids inside the metal)
Almost always trapped gas that had nowhere to escape during casting. Check your sprue and vent placement first — dense areas of a piece need their own escape route, not just a single sprue feeding the whole model. If porosity shows up consistently in the same spot across multiple casts, that spot needs a vent, not a different alloy.
Incomplete fill (thin areas or fine detail didn't cast)
This is a temperature and pressure problem nearly every time — either the metal was too cool when it hit the mold, the mold wasn't hot enough to keep it flowing into fine detail before it froze, or the casting machine didn't generate enough force to push metal into tight geometry. Fine filigree is the first thing to show incomplete fill because it's the first place flowing metal cools and stalls.
Surface pitting or a rough, sandy texture
This is the defect most directly traceable back to burnout. Incomplete burnout leaves carbon residue in the mold cavity, and metal casting against that residue picks up a pitted, contaminated surface. If pitting shows up regardless of which resin or alloy you're using, it's worth re-checking your burnout hold times before changing anything else.
Cracking in the investment (visible before you even pour)
Almost always a burnout ramp that went too fast — see our burnout schedule guide for the specifics. A cracked mold doesn't always ruin the casting, but it does let metal flash into places it shouldn't, meaning more cleanup and a higher chance of a failed cast.
The habit that fixes most of this
Change one variable at a time. It's tempting to adjust burnout, resin, and casting temperature all at once after a bad batch — but that makes it nearly impossible to know which change actually fixed the problem, which means you're likely to see the same defect again in a few months without knowing why.
