Installing Glass Block Windows

Installing glass block windows provides privacy and tons of natural light. Available in a wide range of colors and sizes, glass block windows offers better security and higher energy efficiency than traditional windows.

Types of Glass Block Windows

  • Pre-fab - Local glass fabricators can create custom, pre-made glass block windows to fit any opening. These windows are sized to the whole inch and come wrapped in a metal band. Pre-fab windows are heavy, but easy to install.
  • Glass block - Built in pieces like a brick wall, traditional glass block windows are constructed with grout and individual blocks.
  • Acrylic - Made from clear plastic, acrylic blocks are lighter and cheaper than glass.

Preparing For Glass Block Windows

Although installing glass block is similar to masonry projects, there are important differences. Glass block must be supported by a solid frame and can't be used to create a load-bearing wall. Also, glass block can't be cut to size-the opening must conform to the number of bricks to be installed. As you plan your glass block window project, keep these tips in mind:

  • Accuracy first. Carefully measure the window opening. Measure at three different places (left, middle right) to determine the width and height. Take the smallest measurement from each to determine your window size.
  • A solid foundation. Glass blocks are heavier than standard windows. If you are replacing a window in a wood frame wall, you'll need to double the rough bottom sill and add extra cripple studs below the window opening.

Working With Glass Block

  • Cut the channel. Glass block is held in place with a metal or plastic perimeter channel. Measure the four sides of the window opening and miter cut at a 45-degree angle channel pieces to fit. The top channel piece will need to have a notch cut into it that is one inch wider than you block width and half the depth of the channel material. Carefully cut this notch and save the extra piece.
  • Install the channel. Drill pilot holes in the channel pieces about every foot and install them using one-inch galvanized screws. Make sure the notched piece is installed at the top with the notch facing the interior of the room.
  • Place blocks. Place the first block flush against the channel in one corner to start the first course. Take another block and butter one side with glass block mortar. Place a ¼" tile spacer against the first tile and place the second block into the channel and against the first block, using the spacer to guide your placement. Continue placing blocks until you reach the end of the course. Don't use grout between the blocks and channel.
  • Check the course. Make sure the blocks are plumb and level, using a rubber mallet to gently tap them in place as needed. As you progress, check the mortar of the courses below. When the mortar can resist light finger pressure, remove the spacers and fill the gaps with mortar.
  • Build the window. Continue laying each course of blocks until placed all but the last block. Continue to check each course for level as you progress.
  • The final block. Butter the final block and carefully slide it into place. Apply construction adhesive to the cut section of channel and use it to fill the notch above the last block.
  • Clean up. Tool all of the grout joints with a jointing tool and remove any excess mortar with a damp rag or sponge. Clean the glass thoroughly to remove any haze. Place a thin bead of silicone caulk around the outside edges where the glass meets the perimeter channel.

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