Gaps in the top surface appear as visible holes, thin spots, or incomplete coverage on the uppermost layers of a print. This leaves an unfinished appearance and reduces the structural integrity of the part.
Common Causes
- Under-extrusion on top layers — Insufficient material is deposited to fully cover the surface
- Too few top layers — Not enough solid layers to bridge over the infill structure below
- Insufficient infill density — Large gaps between infill lines make top layer bridging unreliable
- Nozzle partially clogged — Reduced flow creates thin extrusion paths that don’t overlap properly
- Flow rate calibration off — E-steps or flow multiplier not set correctly for the material
Recommended Fixes
- Increase top layer count to 5-7 layers or at least 1.2mm total top thickness
- Increase infill to 25% or higher to provide a stable foundation for top layers
- Increase flow rate by 2-5% if consistent gaps appear across the surface
- Calibrate E-steps and flow multiplier with a single-wall cube test
- Use monotonic top surface fill pattern for even, gap-free coverage
- Slow down top layer speed to 15-20mm/s to allow better material flow
- Check nozzle for partial clogs — perform a cold pull if flow seems inconsistent