How do I build removable wood mullions & muntins?

Written by mark morris
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How do I build removable wood mullions & muntins?
Imitating divided panes adds architectural detail to your windows. (Colonial Window Panes with brick building reflected image by Jorge Moro from

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.

Skill level:

Things you need

  • Tape measure
  • Door stop moulding, 3/4 by 1/4 inch
  • Screen moulding, 3/4 by 1/4 inch
  • Mitre saw
  • Staple gun
  • Sandpaper
  • Latex semigloss paint
  • Fine bristle paintbrush
  • Silicone caulk

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  1. 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 moulding. 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 mitre saw for smooth cuts. Sand the pieces by hand with 150 grit sandpaper.

  2. 2

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

  3. 3

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

  4. 4

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

  5. 5

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

  6. 6

    Sand the entire assembly. Place it on a plastic dust sheet and apply two coats of semigloss paint in the same colour 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. 7

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

Tips and warnings

  • Cut through each piece until it hangs by a narrow splinter. Break this off and trim with a utility knife. This will prevent splintering; small pieces frequently fly when cut through completely.

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