How To Install Window Trim & Aprons | Clean Lines, Tight Miters

Watch finish carpenter Patrick Farrington install a 4-1/2" window casing, stool and apron. This video is all about precision—and this install shows how to get it right without slowing down the job. We’re using Kuiken Brothers Federal moulding profiles, KB104 which is milled from Appalachian poplar in 16' lengths. That means fewer seams, less waste, and cleaner runs across every opening. Everything comes factory primed on all four sides, so there’s no back-priming on site and you can move straight from install to finish. The key here is alignment. Tight miters start with consistent material, but the real difference is how the head casing lands on the legs—and how it lines up with the apron below. When those relationships are dialed in, the entire opening feels balanced and intentional. This is what efficient trim work looks like: better material, cleaner installs, and details that hold up under real jobsite conditions.