How to Trim Aluminum Windows

Adding trim molding around aluminum windows is generally the same process as trimming any other window, except that you can’t nail the trim to the window casing, as aluminum doesn’t hold nails. This can make it tricky to solidly attach the trim, since it has to cover the edge of the aluminum window casing, but you can nail it only to the surrounding wall. Using wide trim (4 inches or more) will help make the project go easier.

Things You'll Need

  • Pencil
  • Tape measure
  • Trim molding (wide)
  • Miter saw
  • Nail gun with trim nails
  • Caulk

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Take a measurement of the top horizontal side of the window, from corner to corner, right along the edge of the aluminum casing of the window with your measuring tape.

Mark two lines on the bottom edge of your trim molding. Leave a few inches of space on the far side of each mark.

Lay the molding on the miter saw with the face up and the bottom edge pressed against the back rail. Line up one of the marks with the blade. Swivel the blade to 45 degrees away from the piece. Cut it.

Slide the molding so the second mark is under the saw. Swivel the blade to 45 degrees in the opposite direction. Cut it.

Hold the molding over the top span of the window, with the bottom edge of the molding lined up with the aluminum edge of the casing, covering it completely. The upper portion of the trim should cover the wall for a few inches.

Secure the piece of molding by shooting nails along the to edge of the piece, every 12 inches or so. Shoot a second nail just below each of the first ones, as far down on the trim as you can go while still being in front of the wall (not the aluminum casing that’s behind the bottom edge of the trim).

Repeat for each side of the window, butting the mitered ends of the molding together at the corners. Caulk the lines where the trim meets the aluminum casing, and where it meets the wall.


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