How Does One Fasten Outside Finish Trim?

The choice between nailing or screwing exterior trim depends on the material used. Nails are better suited for thinner materials like vinyl and aluminum, which are flexible and conformable. For large trim pieces, 15-gauge nails are suitable for attaching wide or heavy exterior trim, such as fascia boards or window casings. For exterior doors, these nails are suitable.

To secure the sill in place, use finishing nails or screws, countersinking each nail or screw so it sits flush with the wood’s surface. Apply another bead of caulk along both sides. To install the top piece of trim, use a rafter square to make two pencil marks around each corner of the jamb, which should follow the right angle of the jamb and be 3/16 of an inch.

Use PVC cement adhesive to secure joints and prevent separation or visible gaps between the boards. The best practice is to use a PVC cement adhesive to keep joints tight and boards secure. Katz provides comprehensive guidance on choosing, installing, and repairing siding and exterior trim.

For thicker, heavier trim pieces, finishing nails provide the necessary holding power to keep the trim securely in place. Brads are better suited for thicker trim pieces. Fasten exterior trim with framing nailer, finish nailer, and staples at different times. Engineered wood must be installed with a 3/16-in. gap between details and then caulked, and fiber cement must be caulked to seal out water.

Exterior coating systems include a Preservative Primer, Flexible Undercoat, and Sealer. Home builders often use wood for exterior trim moldings, but a premium gloss acrylic or oil paint may be more suitable.