In the case of this surface problem, blisters occur on the surface because of trapped solvent. The occurrence of these bubbles can have various different causes.
1. The coats were applied to thick or heavy.
2. The use of unsuitable reducer (too fast).
3. Too short a flash off/drying time between the individual spray coats.
4. Too high an object temperature to accelerate the drying.
5. Too long an air drying time for two components paints before the object is placed in the oven.
6. The use of infra red lamps can cause too high a surface temperature if the lamps are close to the object.
PREVENTION To avoid the occurrence of bubbles the correct reducer for the corresponding spray temperature should be used, and the recommended film build should not be exceeded. Use slower reducers and hardeners when temperature is very hot. It may be necessary to reduce the viscosity when temperatures are extremely hot (i.e. add more reducer), observe the correct flash off times and the drying temperatures, and ensure that there is an adequate distance between the surface and the infra red lamp.
REPAIR Surface damage – solvent pops/bubbles must be sanded down to the level where they occur and affected areas should be repainted. Make sure all bubbles are removed when sanding to avoid having pin holes after repainting the area(s).