Nozzle Buildup, Blobs, and Brown Spots

PETG tends to collect on the outside of the nozzle. The buildup can darken and later drop onto the print as a blob or brown spot.

Fixes

• Clean the nozzle with a brass brush while it's hot.
• Slow down and lower accelerations. High accelerations can make the nozzle scrape material from the previous layer, which balls up on the nozzle.
• Check the first layer. A first layer that's too close to the bed pushes extra material up around the nozzle.
• Dry the filament. Steam from wet filament causes over-extrusion that builds up on the nozzle.
• Use a nozzle sock if your printer has one available. PETG sticks to it less than to bare metal.