Glass Block Installation Technique

Updated April 17, 2017

Glass blocks provide a point of interest and a way to improve light indoors while maintaining privacy. Techniques developed by glass block manufacturers make installation fairly straightforward, using plastic spacers for proper alignment rather than relying solely on mortar. Glass blocks cannot be cut to size, so it is important to fit the project to one of the block sizes available.

Obtain the sizing requirements for the glass blocks from the manufacturer and use a measuring tape to calculate the number required to complete the project.

Frame the space for the glass blocks along the bottom and sides. One board should be attached to the floor and the other boards at 90-degree angles on either end of the floor strip. Cut the boards to size with a saw, drill pilot holes for the screws and use a screwdriver to fasten the frame to the floor, wall and one another. Use a level to make sure the frame is square.

Install joint tape or expansion foam to the inside of the frame as advised by the manufacturer. This is used to cushion the glass blocks if there is any expansion or contraction.

Cut the glass block channel to fit inside the wood frame, using a metal saw. Attach the channel strips along the inside of the wood frame, using the screws provided.

Mix the glass block mortar with water in the mortar pan, as instructed on the packaging, until it is thick and sticks to the glass block without dripping.

Fit the first glass block into the channel strips in one bottom corner of the wood frame and a second into the opposite bottom corner.

Spread 1/2- to 3/8-inch thick mortar on the side of the first glass block that will come into contact with the next block. Do not spread the mortar on top of the glass block or the sides that fit into the channel.

Set the spacer strips in place on the glass block as instructed by the manufacturer. The type depends on the glass block being used as they are specific to each manufacturer. The spacers are usually set where four glass blocks come together. Use tin snips and a file to modify the spacers so they fit.

Continue to spread mortar, and place the glass blocks and spacers to finish the first row.

Spread mortar between the spacers along the top of the first row, taking care not to get mortar on the spacers. Smooth and fill any holes the mortar between the glass blocks using a foam brush.

Continue laying the glass blocks in rows, using the mortar and spacers as instructed until the panel is complete. Check each layer to make sure it is level.

Attach the channel and top board to the frame on the last layer of glass blocks. If the top of the frame is already in place--such as in a window--the top channel can be cut in half and slid into place from either side.

Use a damp cloth to wipe off excess mortar from the glass blocks. Let the mortar set for an hour, then break off the outer tabs from the spacers as instructed by the manufacturer.

Run the striking tool along all the mortar seams to create a smooth, concave seam, making sure to fill in any holes.

Apply glass block sealant with a caulking gun along the space between the channel and the glass block.

Attach decorative moulding to the wooden frame if desired.


Apply the sealant between the frame and glass blocks if the panel is being installed in a moist environment, such as a bathroom. Exterior glass block walls and block panels with curves may require a different technique for installation.


Panels larger than 25 square feet require steel rods between each vertical and horizontal layer for strength. Do not use glass blocks in a load-bearing wall.

Things You'll Need

  • Measuring tape
  • Wood framing material
  • Wood saw
  • Drill
  • Screwdriver
  • Screws
  • Level
  • Joint tape or expansion foam
  • Fine-tooth metal saw
  • Glass block channel
  • Glass block mortar
  • Water
  • Mortar pan
  • Trowel
  • Spacers
  • Tin snips
  • File
  • Polyfoam brush
  • Sponge
  • 3/8- to 1/2-inch striking tool
  • Glass block sealant, optional
  • Caulking gun
  • Decorative moulding, optional
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About the Author

Heather Lindsay is a stained glass artist who holds a master's degree in library science, a bachelor's degree in anthropology with a minor in art, and has enjoyed working in special libraries with photograph collections.