PVC trim expands and contracts with temperature changes, so joints should be assembled to compensate for this. Miter joints are acceptable with this material but need to be held together with fasteners and PVC adhesive.
Apply the adhesive to only one surface and then hold or clamp the pieces together for the recommended setting time. Using glue on both surfaces prevents the cells from fusing in a molecular bond.
Sealing Exposed Edges
Though PVC is considered impervious to moisture, this is not always true. Cut edges can expose open cells that will hold moisture and lead to mildew and algae growth. To avoid this, seal all cut edges by sanding them with 320-grit sandpaper, then wiping the edges with acetone.