Coatings Cafe
Sags
Defect Description
Sags happen when the paint flows unevenly downward on vertical surface.
Paint applied to vertical surfaces undergoes strong downward flow due to gravity. The effect is very strong as the film build increases beyond the sag tolerance film build for the paint. The defect can be seen for example as small drips, heavy curtain sags or small runs below key holes in the part.
Also known as: sagging, drips, runs, curtains
Possible Causes of Defect
1. Film build is too high, especially clearcoat
2. Paint Viscosity is too low
3. Target Distance is too close
4. Booth balance for temperature and air flow
5. Check booth temperature and %humdity for waterborne coatings
Tips to Avoid Defect
-
1. Apply proper thickness -lower film thickness will sag less
2. Run with target paint viscosity at application temperature
3. Maintain proper gun distance
4. Maintain paint booth application process criteria
How to Repair the Defect?
- Consult your specific paint shop procedures.
- Finesse Deck: Sand plus 2-step Polish
- Spot Repair: Sand plus Repaint