DIY Network

How to Add Custom Window Mullions

Add instant interest and traditional appeal to a plain window with custom mullions.

More in Home Improvement

  • Time

    Under Half Day

  • Price Range

    $100 - $250

  • Difficulty

    Easy to Moderate


Step 1: Prepare Windows

Thoroughly clean the inside surface of the windows where mullions will be attached.

Step 2: Measure and Cut

Measure the inside area of the window frame and cut the pine parting bead into two vertical pieces and one horizontal piece to fit the space. The finished mullion will look like an “H” with the horizontal piece extending beyond each vertical.

Step 3: Assemble and Paint

Notch the strips where they cross and attach together with a small tack nail. Paint both sides of mullions with paint in a color to match existing window trim.

Step 4: Install in Windows

Attach the mullions to the inside of the window with small pieces of clear double-sided tape. For a more permanent hold, drive small tack nails through the mullion corners into the inside edges of the window frame.

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