This is old coating material lifting, sweating, or swelling when new coating is applied. It sometimes occurs around the edges of primers, body fillers, or stopper spots. It may appear during painting or the drying time.

Causes

The possible causes of these swelling edges are:

1. Recoating of solvent-sensitive layers (NC/TPA) with wrong repair materials or excessive thickness.

2. Coats used as a sealer are not thick enough.

3. The filler was sprayed too thick and not allowed to dry sufficiently.

4. The old substrate is weak or not cured.

Prevention

Check the old substrate to ensure it is sound and apply correct film thickness when using products. When using a sealer, it is better to cover the entire panel with correct film thickness to form a barrier between the old and new surfaces. Also, observe adequate flash-off time.

Repair

The affected areas must be sanded down and refinished (filler and top-coat).