Seam sealer is the component that most restorations skip in the interest of time and that shows up as rust within five years. The factory applied seam sealer to every body joint that could trap moisture — the roof-to-quarter panel seam, the floor pan to rocker joint, the trunk floor seams.

The correct application: the seam sealer goes over the primer but before the topcoat. It should be worked into the seam with a tool, not simply wiped across it. The goal is to fill the joint completely, not to cover it cosmetically.

For under-body seams, the seam sealer should be top-coated with rubberized undercoating after it has fully cured. This provides a second layer of moisture protection and makes the result look correct.