Visible horizontal cracks appear in the print, or the part splits cleanly along layer lines when bent or loaded. Sometimes it separates during printing itself; sometimes only when you try to use the part. See the Layer Adhesion guide for weak-but-not-separated layers — this guide covers visible cracking and complete layer splits.
Distinguish From Layer Adhesion Failure
Layer separation = visible gap or crack between layers you can see or feel. Layer adhesion failure = layers are bonded but the bond is weak and breaks under stress.
Both usually trace to temperature, but layer separation is more severe and often has a different triggering cause.
ABS Is the Most Common Victim
ABS delaminates. It’s not a settings problem — it’s physics. The large thermal coefficient of expansion means layers contract significantly as they cool, and if the thermal gradient is steep enough (cold ambient, aggressive fan, tall print), the internal stress overcomes the inter-layer bond. The crack appears on the layer that cooled fastest relative to the one below it.
If you’re printing ABS without an enclosure and seeing layer separation, the enclosure isn’t optional. A 40°C chamber temperature reduces the thermal stress by more than any temperature or fan setting change.
Fix Sequence
1. Raise nozzle temperature 10–15°C. More heat means more remelting of the layer below, stronger bond. For ABS at 240°C, try 250°C. For PLA (less common but possible with aggressive fan), try 215°C. Don’t exceed material limits, but most published maximums are conservative.
2. Reduce fan speed drastically. ABS and ASA: fan off entirely, or 15% maximum. Even PLA can delaminate at 100% fan in tall, thin prints where each layer is very small and cools before the next layer arrives. For tall, thin PLA prints that are splitting, try 50% fan.
3. Add an enclosure. Even a cardboard box around an open-frame printer reduces the ambient drop enough to help. A full enclosure holding 40–50°C chamber temperature virtually eliminates ABS delamination.
4. Reduce print speed. Slower means more time at print temperature per layer, less thermal gradient. At 80mm/s vs 40mm/s, the time between successive layers on a small cross-section part can halve. Slower = more heat retained.
5. Check for wet filament. Moisture creates steam bubbles at the layer interface that mechanically prevent bonding. Signs: audible popping during printing, rough surface texture. Dry the filament (PLA 45°C/4h, PETG 65°C/6h, ABS 80°C/4h) and test immediately on a fresh spool.
When the Separation Is Mechanical, Not Thermal
If you see separation only in one location on every print — same height, same side — check for a draft. An air vent, open window, or fan blowing directly at the printer can cause localized delamination on the windward side. Block the draft and the problem disappears.