How to Mull Windows


Mulling two or more windows together is technically just fancy words for joining the windows together. This allows for a larger window view that is not obstructed by a wall or other structure between the windows. Some homeowners choose to have the mulling process completed at the factory when they purchase the windows. Another option is to purchase a mulling kit and mull the windows together yourself. Before beginning the mulling process, read the manufacturer recommended installation to achieve the best results.

Things You'll Need

  • Blanket
  • Pliers
  • Mulling kit
  • Rubber mallet
  • Screwdriver
  • Power drill
  • 3/16-inch drill bit
  • Sealant container
  • Caulking gun
  • Cover a clean, sturdy surface with a blanket. Lay the windows wood side down on the blanket. Match the sills and heads of the two windows together.

  • Snap the nail fins off the sides of the windows that you are joining together. Pull the nail fins forward and then backward with a pair of pliers until the nail fins snap off. Push the windows together so the sills and heads are flush to each other.

  • Insert the mull pin in the middle of the nailing fin channel and slide it down all the way. Use a rubber mallet to gently pound the mull pin into the nailing fin channel if needed. Place the mull plug between the two windows with the injection hole facing the exterior.

  • Loosen the two screws that are located on the bottom area underneath the mull pin. Place the bracket over the bottom two screws that you loosened. Tighten the two screws.

  • Use a power drill with a 3/16-inch drill bit and drill a hole in the windows. Use the hole at each end of the bracket as a guide to where to drill the holes. Install rivets in the two holes you just drilled with a rivet gun.

  • Install the mull cover over the gap between the two windows. Use a rubber mallet to gently pound the cover if needed. Flip the joined windows over carefully and install the mull cover on the other side.

  • Load a sealant container into a caulking gun. Place the nozzle inside the mull plug and inject the sealant. Stop injecting the sealant when it leaks out of the fin channel.

  • Start at the corner of the frame that is perpendicular from the mull and slide the nail fin until it is flush against the other, and cover the mull plug.

  • Apply the connector and structural brackets as stated in the manufacturer recommended installation.

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