How To Install Interior Vinyl Window Casing. Away from the jamb at both ends and along the base of the window casing. Get the Spacing Right.
With a hammer or mallet lightly tap against the whole length of the casing until it is flush against the wall. Nail the thick part of the trim to the framing with 2-in. 100 lead-free durable virgin PVC.
With the arch clamped in place draw a line between the inside and outside marks for the miter cut on one side.
Place the top piece and hold the trim 316 in. Step 1 Clean up the area where the jamb extender will be installed and prep out the space. This creates a thin shadow line surrounding the window frame that delineates the window frame from the wall. For linear trim cut the side casings straight across so that they can be installed right between the head casing and sill.