Foundry

Gilsonite and Common Casting Defects

May 21, 2026 · 1 min read · Sun Gilsonite Technical Team

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Carbon additives affect several casting defects. Getting the level right is key.

Defects reduced by gilsonite

Burn-on / burn-in – rough sand adhering to the surface
Metal penetration
Scabs and rat-tails – related to sand expansion; carbon additives help cushion expansion
Poor shake-out

Monitor LOI, volatile content and casting quality. Adjust gilsonite additions in small steps.

Defect	Possible additive-related cause	Action
Burn-on	Too little carbon	Increase additions
Blowholes	Too much gas	Reduce additions, check moisture
Lustrous carbon folds	Excess volatiles	Reduce additions on thin sections
Scabs	Sand expansion	Maintain carbon level, check clay
Rough surface	Low carbon or coarse sand	Adjust carbon and fineness

Many defects have several causes. Change one variable at a time and record the results.

Data sheet

Data sheet – Foundry Grade Gilsonite
Property	Typical value	Test method
Appearance	Black powder	Visual
Particle size	100 – 300 mesh	Sieve
Volatile matter	55 – 75 %	ASTM D3175
Ash content, max	5 %	ASTM D3174
Moisture, max	1 %	ASTM D95
Softening point (R&B)	150 – 200 °C	ASTM D36
Typical dosage	0.3 – 1.0 % (iron)
Packing	25 kg bags palletized; 1 MT jumbo bags for blending plants.

Typical values. The final specification is confirmed in the COA of each shipment.