How to Install Glass Block Windows

Homeowners who learn how to install glass block windows can save money and add beauty and privacy to any room. Glass block windows come in a number of sizes and styles, making it easy to customize the look to match your home's design.

How To Install Glass Block Windows The Easy Way

Although you can install glass blocks individually like traditional masonry blocks, when it comes to windows, pre-fabricated glass block window units are far simpler to install. Most large home centers can custom order pre-fab glass block windows or you can order them from a local glass fabricator. Getting started is easy:

  • Accuracy is crucial. Carefully measure the window opening from the rough frame. Measure at three different places to determine the width (top, middle and bottom and height (left, middle and right). Take the smallest measurement from each to determine your window size. Also, make a sketch of the window to carry with you when you order your glass block window. And remember to leave a ½" border around the window for cement.
  • A solid foundation. Glass blocks are heavier than standard windows. If you are replacing a window in a wood frame wall, you may need to reinforce the rough bottom sill by adding cripple studs below the window opening. A glass fabricator can tell you if you'll need such reinforcement based on the size of the window.
  • Out with the old. To begin installing your glass block window, you'll need to remove the existing window and finished frame. You'll want your window opening to be bare down to the rough frame, removing any old hardware, adhesives or bits of wood. Clear away any dust or other debris left behind.
  • Prepare the sill. Place cedar shims in two or three spots along the bottom of the window opening to create a ½" gap. Dampen the shims and the bottom of the window opening with a spray bottle of water. Apply a layer of cement mortar along the bottom of the window opening, flush with the tops of the shims. Be sure to use cement (Portland cement, sand and water) and not bricklaying mortar-cement is stronger and will support the weight of the window.
  • Placing the new window. Carefully lift the glass block window into place and set it on the shims and the layer of cement. Glass block windows are heavy, so be sure to enlist the help of several friends. Place a few shims into the top gap until they are just tight. Position the glass block window so it is plumb and square, parallel to the wall and sticking out equally on both sides of the opening.
  • Add cement. Using rubber gloves and a small trowel, pack the sides from top to bottom with cement. Do not put cement into the top opening, but make sure the sides and bottom are filled, leaving no gaps. After a half hour or so, tool the cement along the sides and bottom with and old spoon or your finger-create a smooth surface. After two hours, gently remove the bottom shims and fill the gaps with cement, making sure to smooth the surface afterward. Excess cement can be removed from the glass blocks with a damp sponge.
  • Finishing up. After the cement has dried for 24 hours, you can fill the top gap with silicone caulk. Place foam backing rods in the gap, ½" deeper than the wall surface and then fill the remaining gap with caulk. Excess caulk can be removed from the glass blocks with denatured alcohol. Apply trim around the window if desired.
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