Repair an imported mesh

Fix a model that imports “not watertight” so it can be sliced and used in booleans.

A watertight model is one whose surface is completely closed, with no gaps — the only kind a slicer can fill and the only kind that can take part in a boolean. Downloaded and scanned models are very often not watertight, and the commonest cause is invisible: the file stores each surface twice with the last decimal place disagreeing, leaving hairline cracks along the seams. **Repair** welds those cracks shut, closes real holes, removes zero-area and duplicated faces, and turns around any face pointing the wrong way. It is one undoable step, so Ctrl+Z puts the original back. It will never make a model worse — if repairing would fuse two parts that merely touch, the repair is discarded and the model is left alone. Where it cannot help is an edge shared by three or more faces, which has no single right answer; if the repair says the model is still not watertight, that is usually why. **Rebuild as solid** is the fallback, offered on that message. It re-wraps the model in a brand-new closed surface, which always works — including for models that overlap themselves — but it replaces every triangle, so sharp edges soften and fine detail is lost. It also takes seconds to minutes, and asks before it starts. Try Repair first; reach for Rebuild only when Repair has already told you it fell short.

1. Import the file. If it is not watertight, the import notification says so and offers Repair.
2. Missed the notification? Select the mesh and press “Repair mesh” in the properties panel.
3. For a whole model, run Print check — it lists every broken mesh with one button to repair them all.
4. If the repair reports it is still not watertight, take the “Rebuild as solid” offer on that message.