First layer keeps peeling at the corners on PLA — is it bed adhesion or warping?

Question

My first layer looks great in the middle but every corner of a 150 mm flat bracket lifts about 1 mm after ~20 layers.

Printer: Bambu Lab P1S, textured PEI plate
Material: PLA, 220 °C nozzle / 55 °C bed
Enclosure door open, room at 21 °C

I already washed the plate with dish soap and water. Is this classic warping or is my Z-offset too high? Photos show the corners lifting cleanly, no elephant foot.

Marcus Weber · Accepted Answer

Corners lifting cleanly = thermal contraction pulling the part off , not a Z offset problem. A few fixes in order of effectiveness: 1. Close the door and turn on the aux fan only after layer 5 — PLA with the door open in a 21 °C room cools too fast on large flat parts. 2. Add mouse ears 5 mm discs, 0.4 mm tall at the corners in your slicer, or a 3 mm brim with a 0.1 mm gap. 3. Drop the bed to 50 °C. Counter intuitive, but 55–60 °C on PLA softens the bottom layers and they let go easier. A 150 mm flat bracket is close to the size where PLA always fights you; if it's a production part consider PETG or PA CF.

Lukas Novak · Answer

Adding to Marcus: check the plate with IPA after the soap wash. Dish soap leaves a surfactant film on some textured PEI plates that reads as "clean" but kills adhesion at the edges where the bed is 3–5 °C cooler than the centre.

Hannah Lee · Answer

Closed the door, 50 °C bed, mouse ears — zero lift on the next print. Marking as accepted, thank you both

First layer keeps peeling at the corners on PLA — is it bed adhesion or warping?

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