TIP: How to Avoid Runs and Sags
You should never have runs or sags drying in your finish whether you’re brushing or spraying. The way to achieve this level of perfection is to watch the surface you’re brushing or spraying in a reflected light. You may need to arrange some lights or move your body and your head often to see what’s happening.
With a reflection you can see easily when a finish begins sagging or running. Then it’s a simple matter of using your brush (even if you’re spraying) to remove the problem. Lift the excess finish off the surface with the brush and spread it to another part or drag it over the lip of a jar or can.