Paint Sags

Paint sags occur when too much paint is sprayed onto an upright panel and begins to sag, usually causing a smile shaped ridge which is a high point in the paint. Sags can be flat-and-polished out.

What it means

Paint sags are areas where fresh paint or clearcoat has been applied too wet or too heavily so it slowly creeps down the panel before it dries. Instead of forming a sharp drip like a classic paint run, the material slumps and gathers into softer, wavy ridges or bulges. You can usually see and feel a sag as a thicker, uneven section that distorts reflections compared with the surrounding paint.

Why it matters

• Ruins the flatness of the finish: Sags disturb the smooth, even surface that good paintwork needs for sharp reflections and a quality look.
• Needs rectification work: Properly correcting sags normally involves local wet sanding to level the excess and then machine polishing to restore gloss.
• Hints at application issues: Sags often point to problems such as too slow a thinner, too much material, the gun held too close or poor control on vertical panels and edges.

Where you’ll see it

You will see paint sags mentioned on bodyshop quality control sheets and rectification notes, usually alongside paint runs and other spray defects. Customers might describe them as waves, droops or thick patches in the paint. They are most common on doors, wings, bumpers and other vertical or curved panels where paint can naturally gather and sag.

Context

In refinishing language, paint sags are closely related to paint runs, but are usually broader and less defined. Both sit in the same family as orange peel, dry spray and dust nibs as defects that may need flat and polish work. Minor sags can often be carefully wet sanded and polished, while heavier sags, especially on edges and body lines, may require the area to be repainted if too much material would need to be removed to level them safely.

Common mistakes

• Treating broad sags as if they were simple swirl marks and trying to polish them out without first levelling the excess paint.
• Sanding aggressively over a sag on an edge or body line and breaking through to primer or basecoat while chasing the last trace of thickness.
• Repainting over existing sags without flattening them first, which just buries the defect under more material and can make the panel look even more uneven.
• Repeating the same gun setup and technique that caused the sag in the first place, leading to repeat defects on the same panel after repair.

Written by Danny Argent. Last updated 18/11/2025 19:16