What is seam sealer primarily used to do?

• A. Fill deep scratches
• B. Improve adhesion of primer
• C. Seal joints and prevent moisture intrusion
• D. Remove corrosion

Answer: (C)

Seam sealer is a flexible sealant applied to vehicle body seams and joints to block moisture and air from seeping into the panels. Its main job is to seal gaps between welded or joined panels, around frame and windshield areas, so water can’t penetrate and cause rust under the finish. It also helps the paint system by keeping moisture out and accommodating the slight movement of metal from temperature changes and vibration, keeping seals watertight over time. It isn’t used to fill deep scratches, which is what body filler does. It isn’t intended to improve primer adhesion, which comes from proper surface prep and compatible primers. And it doesn’t remove corrosion—that’s done by rust removal and treatment before sealing.