How do I Build Removable Wood Mullions & Muntins?

Mark Morris

Divided panes can add detail to an otherwise plain window. Mullions are the large horizontal dividing pieces at the top of the bottom sash frame and the bottom of the top sash that divide the window in half. Muntins are the small dividers that actually separate the individual panes of glass. Creating faux dividers is a project that most homeowners can tackle with a little bit of planning and some careful measurements. Mullions are typically already present. Creating removable muntins is the simple way to achieve the desired effect.

Imitating divided panes adds architectural detail to your windows.
  1. Measure the window you would like to add faux divisions to. Measure from inside to inside of the sash from side to side and top to bottom at the surface of the glass. Cut pieces from ¾-by-¼ inch door stop molding. This is used for window jambs and door jambs and can be purchased at any lumber retailer. Cut one piece the height of the sash inside to inside. Cut one piece the width of the window, minus ¾ inch. Cut this second piece in half. Use a miter saw for smooth cuts. Sand the pieces by hand with 150 grit sandpaper.

  2. Measure and cut ¾-by-¼ inch screen molding. Cut one piece to fit horizontally inside the sash frame. Fasten the two pieces of ¼-inch door stop molding to the back of the screen molding with a staple gun, flush at each end, leaving a ¾ inch gap in the center. Use a staple every six inches.

  3. Position the vertical door stop molding at a 90-degree angle to the horizontal divider assembly. Adjust the pieces until they cross in the center of the vertical piece. Staple them together with two staples in the center.

  4. Cut two pieces of screen molding the length of the ends of the vertical divider from the horizontal screen molding to the ends of the vertical door stop molding, plus 1/8 inch on each piece. Cut a miter at one end of each piece, with the molding standing on edge to create a chiseled tip.

  5. Align the mitered pieces so that the chiseled tips are against the edges of the horizontal screen molding to create a tight joint. Staple through the back of the vertical stop molding to attach them, with one staple every six inches. Cut the ends flush on the miter saw, if needed.

  6. Sand the entire assembly. Place it on a plastic drop cloth and apply two coats of semigloss paint in the same color as the window frame. Use a fine bristle brush and apply with long, straight strokes, spreading the paint as evenly as possible to prevent runs and drips. Allow the label-recommended drying time between coats.

  7. Apply a pea-size bead of silicone caulk at the end of each of the four cross members and one at the center. Fit the muntin assembly into the window sash and press in place firmly to adhere the silicone to the glass.