Also known as: Curtains, Drips, Tears.
What it looks like
Drips, curtains or teardrop shapes on vertical and inclined surfaces, usually with a thick lower edge. Above the sag, the film is often thinner than specified.
Common causes
- Applying too much paint in one pass
- Paint thinned too much, or used outside its temperature range
- Spray gun held too close or moved too slowly
- Low temperatures slowing the drying, so the film stays mobile longer
Why it matters
Runs are not just cosmetic. The thick areas may not cure properly and can crack, while the area above may be below the minimum film thickness. Both shorten the coating’s life.
Prevention
- Check wet film thickness regularly during application
- Keep to the data sheet’s thinning and temperature limits
- Apply several correct coats rather than one heavy one
- Train applicators in gun distance, speed and overlap
Repair
Before cure, runs can sometimes be brushed out. Once cured, the sag should be abraded smooth and the area recoated, with film thickness checked afterwards.
Inspector’s note
Runs often come with excessive total film thickness nearby. A dry film thickness survey of the surrounding area is worth doing.