After spraying, do the paint surfaces show streaky "tear marks"? Sagging not only ruins the appearance but also creates hidden risks to coating performance. As a professional manufacturer, we provide an in-depth analysis of the three major causes of sagging: low viscosity, excessive film thickness, and incorrect spray technique, along with practical on-site correction tips.
In coating construction, nothing is more awkward than the occurrence of "sagging" during film drying. Such tear-like marks usually appear on vertical surfaces or at the edges of complex components.
As an industrial paint manufacturer, we break down the three core variables behind sagging for you, helping you achieve a perfect coating with "no dripping paint":
1. Viscosity Control: More Thinner Is Not Always Better
- Question: In pursuit of smooth spraying, many applicators add excessive thinner. The paint becomes too thin, causing the paint film to rapidly sag under the influence of gravity.
- Countermeasure: Use Zahn Cup #4 to measure viscosity. Different types of industrial paint have their optimal spray viscosity (usually between 18-25 seconds). Only with proper viscosity can the paint film "stand" on the substrate.
2. Spray Gun Gesture: The Art of Distance and Angle
- Problem: The spray gun is too close to the substrate, or it stays at one point for too long, causing the local paint amount to exceed the limit instantly.
- Problem: The spray gun tilt angle is too large, causing uneven paint mist distribution.
- Countermeasure: Keep the spray gun perpendicular to the substrate, with the distance maintained at 20-30 cm. The movement speed should be steady, following the principle of "edges and corners first, then flat surfaces", and the overlap of each pass should be controlled at 50%.
3. Applying the coating too thickly in one pass: More haste, less speed
- Question: Attempting to achieve the design thickness in a single spray pass (especially when the wet film thickness exceeds 150 microns) will inevitably cause the entire coating to sag due to gravity.
- Countermeasure: Adopt **"thin spraying in multiple passes"**. Spray a thin "mist coat" as the grip layer for the first pass, then spray the second coat after flash-off.
4. On-site First Aid Plan
- Wet film condition: If sagging signs are found right after spraying, gently smooth it with a clean brush and immediately re-spray.
- Dry film condition: The paint film must be completely dry, then sand the sagging area smooth with sandpaper and re-spray the entire surface.
Conclusion: Sagging is the touchstone of technical maturity. Through precise viscosity ratios and standardized spraying techniques, every applicator can achieve an industrial protective coating as flat as a mirror surface.