How to Install Glass Block Windows

Glass block window

Glass block windows are a smart alternative to traditional windows, especially for bathrooms and basements. Glass blocks are available in a number of sizes, shapes, patterns and colors, providing homeowners with the opportunity to create a unique window. Glass block windows enhance curb appeal, and because they are far less breakable than typical glass windows, they offer far greater home security. When properly installed, glass block windows are energy efficient, easy to maintain and leakproof. And not only do they offer more privacy – without sacrificing the beauty of natural light – but glass block windows are also relatively simple to install.

Before You Begin a Glass Block Window Installation Project

  • Take preliminary measurements, noting the width and height of the opening to determine the size and number of glass blocks you need.
  • You may want to sketch a design or diagram on paper, allowing approximately 1/4 inch of space between each block, the frame and the wall. (This leaves room for spacers.) If you cannot come up with a uniform block configuration to fit the space, you may need to get creative, using smaller blocks and/or other material to fill extra space.
  • Assemble tools and materials. A detailed list of items you’ll need is included at the end of the following step-by-step instructions for installing glass block windows.

Step-by-Step Instructions: How to Install Glass Block Windows

  1. Completely remove the existing window, including the frame.
  2. Use a tape measure to measure the opening from the outside.
  • Measure each dimension carefully, including depth. Check to make sure the opening is plumb and square.
  1. Cover the opening with plastic until the new window is ready to install.
  2. Build a new frame to match the dimensions you measured. You’ll use this frame to mortar your glass blocks inside before you install the entire unit as one piece.
  3. Attach glass block channels (plastic tracking) to the frame:
  • Cut three lengths of plastic tracking to fit the bottom and both sides. Install these by adding a bead of silicone on the backside of the channels before screwing them to the frame.
  • Next, cut a piece of channel for the top of the frame.
  • For the top channel, measure one inch from the inside edge and cut the channel straight down its entire length, to create a small L-shaped piece and a larger L-shaped piece. Set the small piece aside for now. You’ll use it later to sandwich your top row of blocks.
  • Screw the larger piece into the backside of the top of the frame. Again, for best results, use silicone before installing.
  1. Install blocks using either silicone (100 percent pure clear silicone) or glass mortar. Either method will require a set time of at least 24 hours.

To use silicone:

  • Place a silicone bead along the bottom of the channel.
  • Place the first glass window block in the bottom left corner, followed by a spacer placed vertically on the right side of the block. (Trim the spacer if necessary.) 
  • Place the next block in, fitting it snuggly next to the spacer and within the channel. Again, follow with a vertically placed spacer. Continue this process until the bottom row is complete.
  • Place two parallel beads of silicone on the bottom of a horizontal spacer, and place the spacer evenly on top of the bottom row. Run two more parallel beads of silicone on top of the spacer; then place the second row of blocks on top, again with vertical spacers between. Repeat this to build each row.
  • Once you have installed the top row, apply silicone to the inner edge of the remaining half of your top channel/tracking, and push it into place on the top of the frame.
  • Seal the blocks by applying silicone sealer. Apply this to the horizontal seams first. Next, apply it to the vertical seams. Avoid applying too much, especially in the horizontal spaces that have already been filled in.
  • Repeat the silicone sealer process on the other side of the window.
  • Use a plastic putty knife to smooth the sealer, and wipe excess silicone away using a damp cloth.

To use glass mortar:

  • Mix the glass mortar, following the manufacturer’s instructions – it should be not thin and runny but also not too pasty.
  • Apply a thin layer of mortar to the left side of the bottom channel, and place a glass window block in the left corner, followed by a spacer on the right vertical edge.
  • Apply a thin layer of mortar to the right side of the block and spacer, and then add the next block and spacer. Follow this process until the bottom row is filled in.
  • Place a horizontal spacer on top of the bottom row, adding a thin layer of mortar on top, followed by glass blocks. Lay the next row as you did the first.
  • Continue until all blocks have been installed. Once the top row is complete, apply a small bead of silicone to the remaining half of your top channel/tracking that you set aside earlier, and push it into place on the top of the frame.
  • Apply silicone sealer to the joints, starting horizontally, then vertically. Use a plastic putty knife to smooth the sealer and a damp cloth to wipe off excess.
  • After the window has set for 24 hours, it is ready to be installed and trimmed.

Items You’ll Need to Install Glass Block Windows

These tools and materials are the essential supplies you need for following the above process.


  • Tape measure
  • Hand saw or circular saw (for building window frame)
  • Caulk gun
  • Cold chisel
  • Trowel
  • Drill and/or screwdriver
  • Wood screws
  • Level
  • Wrecking bar
  • Utility knife
  • Plastic putty knife


  • Glass blocks
  • Latex caulk
  • Silicone sealant (100 percent pure silicone highly recommended)
  • Glass block channels (plastic tracking)
  • Spacers
  • Anchors (if needed for screws)
  • Wood trim
  • Mortar

Other suggested items

  • Gloves
  • Bucket
  • Safety glasses
  • Spray bottle with water
  • Damp cloth(s)

Update Your Home’s Windows with Help from Glass Doctor

From mixing mortar to building a frame, installing glass block windows is no simple task. Feeling overwhelmed by this project? You can avoid the hassle and frustration without giving up the beauty and security of glass block windows. Call Glass Doctor at (833) 365-2927 for a window installation quote today. Alternatively, you can contact your local Glass Doctor or schedule an appointment online to learn more about your glass block window options.

From windows to bathroom ventilation, keeping chilly air out, warm air in, and water right where it belongs is a big job. Learn the signs that it’s time to recaulk your bathroom in this blog from Mr. Handyman: When Is It Time to Recaulk Your Bathroom? Like Glass Doctor, Mr. Handyman is part of the Neighborly family of trusted home service professionals.