Hiding Mitered Corner Cuts
The picture-frame look is what most homeowners want — and the hardest to keep tight. Here's how to hide the miter instead of chasing an impossible seam.
A picture-frame deck with mitered corners is the look most homeowners want, and the hardest to keep tight. Even a flawless miter is only flawless for one season — as the boards move, the seam opens. Rather than chasing a seam you can't win, the reliable approach is to cover the miter with a cap made for that exact angle.
Why the perfect miter doesn't stay perfect
A mitered corner joins two boards at an angle to create that clean, continuous picture-frame edge. The problem is that both boards are moving: as they expand and contract with the seasons, the two halves of the miter shift relative to each other and the joint opens. The cut isn't the failure — the movement is. That's why sanding, gluing, or re-cutting a miter tighter only buys you until the next temperature swing.
Cover the cut instead of chasing it
The finish that actually holds is a cap sized to the corner. It sits over the miter so the joint is hidden, while the boards underneath stay free to move. Instead of a seam that looks sharp in summer and split in winter, you get one clean detail that reads the same all year.
Match the cap to how your boards meet
GAPCAP comes in three angles so the cap matches the corner exactly:
- 0° — for straight runs where two boards meet in a line.
- 45° — for angled corners, the classic mitered picture-frame corner.
- 90° — for square corners.
And there are two pieces working together, each offered in all three angles: TopCap covers the top surface of the corner, while FasciaCap covers the fascia-facing edge. Use them together and the entire mitered corner — top and side — reads as one intentional, finished detail, in Black, Gray, or Brown to match the deck.
Frequently asked questions
Even a perfect miter is only tight for the season it was cut in. As boards expand and contract, the two halves of the miter pull apart and the seam opens. It's the movement, not the cut, that opens the corner.
GAPCAP™ comes in three angles: 0° for straight runs, 45° for angled corners, and 90° for square corners. Every angle is available in both TopCap and FasciaCap — match the cap angle to how your boards meet.
TopCap covers the top surface of the corner, while FasciaCap covers the fascia-facing edge. Used together they hide the whole mitered corner as one clean detail.
