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To determine kit size, measure window and add about 2" on each side; for example, a 44" kit fits a standard 40" window. Styrene cornices can be trimmed easily using a saw blade or serrated kitchen knife. If a different design is preferred, the boards can be cut using a saw blade or a serrated knife. In this case, the crew didn't want such a wide cornice, so they simply trimmed away some of the styrene shape.
Attach the front cornice piece to the two side "returns." Most products suggest using low-temp hot glue. Some kits come with polystyrene glue, which will need to dry before continuing.
When cutting, allow about 1" extra on all sides. Typically, a solid or non-directional fabric can be used across the fabric width -- getting two boards out of about 1-3/4 yards of fabric. Iron material to remove wrinkles. Measure and cut fabric to cover the inside of the cornice, if desired.
Lay cornice board face-up and place fabric on top, centering it over the cornice. Use the cornice kit tool or a plastic putty knife to tuck the fabric in along the styrene seams. Adjust the fabric if necessary. When the fabric is secure on the front, continue along the sides. When the outside is done, pull the fabric around to the back of the styrene pieces and secure. You can also pin or use low-temp hot glue to secure, if necessary. Trim fabric as necessary to miter corners.
Add any desired trim: braiding, cording, fringe, etc. If these go along the styrene seams, they can be tucked in place, like the fabric. Or use pins or low-temp hot glue to secure. Cover the inside of the cornice in the same manner if desired using fabric adhesive, spray glue or low-temp hot glue to secure.