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.

Use scarf or "weather cut" joints to join long lengths of trim
end-to-end. Leave the joint unglued so that the boards can expand and contract
without visually opening up.
Use scarf or "weather cut" joints to join long lengths of trim end-to-end. Leave the joint unglued so that the boards can expand and contract without visually opening up.


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.

Ripping PVC trim exposes the open interior cells. If left unsealed,
these can absorb moisture, allowing mildew and algae to develop, as shown in this photo.
Ripping PVC trim exposes the open interior cells. If left unsealed, these can absorb moisture, allowing mildew and algae to develop, as shown in this photo.

To learn more about Exterior Trim, visit the JLC Field Guide.