Runs and Sags


Paint material drips or sags down the side of a vertical panel. Also called hangars or curtains.

There are several reasons why runs and sags can occur. They are:

  • Improper choice in reducer or too much reducer: It is important to choose the appropriate reducer for the type of material being sprayed and the shop conditions in which they will be sprayed. Reducer that evaporates too slow and excessive use of reducer are the primary causes of runs and sags.
  • Excessive film thickness: Piling on too much material in full wet coats is a common cause of runs.
  • Insufficient flash time: Not allowing enough time for solvent to flash off of first coat before applying next coat can also cause runs.
  • Insufficient air pressure: Failing to maintain adequate enough air pressure at the tip of the gun can cause paint to run or sag. Also important is use of the correct fluid tip and air cap, and even type of gun for the specific material.
  • Poor technique: Any number of factors including the position of the gun tip, the speed of the pass, the degree of overlap between passes, the distance of the gun from the panel, etc. can cause runs and sags.

If the paint is still wet, remove with solvent, clean the area and reapply coating. If the paint has already dried, sand out any runs, sags or other imperfections and reapply coating.


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