Looking for a How To on a Glass Block Window Installation?

So you need a glass block window installed at your home? There are two ways you can go about completing this project. Option one you can head to Google and search for things like “glass block installers near me”. Find a reputable installation company and have them install the glass block window for you. Or option two would be heading to Google and searching “how to install glass block”. Which is probably how you ended up on our page!

By following the steps below you can install you’re own glass block window!

The tools required for the mortar glass block window installation system are a margin trowel, mortar pan, polyfoam brush, sponge, tin snips, screwdriver or power drill, fine tooth saw or miter saw, caulking gun, utility knife, metal file, tape measure, 3/8″ to 1/2″ striking tool and 2′ level.

glass block window installlation

1. Prepare The Rough Opening for The Glass Block Window Installation

A. Make sure the opening is the correct size. To determine the correct size of the rough opening, add 1/4″ to the sum of the nominal block sizes for both the height and width.

Example: Panel (using 8″ x 8″ block) is four block wide (8 x 4 + 1/4″ = 32-1/4″) and five block high (8 x 5 + 1/4″ = 40-1/4″). Rough opening needs to be 32-1/4″ wide and 40-1/4″ high.

B. Use a level to make sure the opening is level and plumb.

C. Measure the opening diagonally from corner to corner in both directions, and compare the glass block dimensions to check for squareness. These dimensions should be equal to within 1/8″

2. Install Perimeter Channel

A. Cut the channel to fit the perimeter of the opening. The channel ends may be cut straight or mitered.

If cutting the ends straight:

  • Cut the top and bottom channels to the width of the opening.
  • Cut the side channels to the height of the opening minus 1-1/2″ so they will fit between the top and bottom channels.

If mitering the ends, make all cuts at a 45° angle.

B. Cut the top channel in half lengthwise with a utility knife. Score the center groove with the knife and break the channel in half. Apply glass block sealant to back of channel before installing

C. Install the bottom channel:

  • The channel may be installed in the center of the opening, or flush with the interior or exterior side of the opening.
  • Attach the channel to the opening by inserting #6 x 1″ flat head galvanized screws or equivalent through the predrilled holes in the channel. Insert two screws in each end of the channel.

D. Install the side channels in the same manner making sure they are plumb before attaching with screws

E. Install the half top channel:

  • Place the half channel in the top of the opening making sure it is aligned with the side channels.
  • Attach the channel to the opening by inserting #6 x 1″ flat head galvanized screws through the predrilled holes in the channel. Insert a screw at each end of the channel.
  • On exterior windows, the screwed in half channel should always be the exterior side.

F. Paint all of the screw heads white to reduce their visibility.

3. Preparation of Universal Mortar Spacers

A. Assemble the spacers for the series of block you are installing. The spacers come in two halves, snap the spacers together to fit the width of the block.

B. Modify the spacers using tin snips based on their location:

  • Where four block come together, spacers are used as assembled. These are called “REGULAR”.
  • Where block meet the side perimeter channel, clip off both sets of smooth legs. Twist-off tabs remain in place. File off any burrs so the spacer will lay flat. These are called “FLAT”.
  • For the top row of block, clip off one upper toothed leg and cut the twist off tab in half. These are called “H”.

This is a reference guide for where “REGULAR” and modified spacers are used.

4. Mortar Preparation

Mix mortar according to the instructions on the premix mortar bag. When mixed to the proper consistency, mortar should stick to the edge of the glass block when turned on edge.

Be sure to read and understand all precautions outlined by the mortar manufacturer. Freshly mixed mortar may cause skin irritation.

*Want to learn more about mortar? Check out our blog, What is Mortar?, to learn about what mortar is and why we use it!

Glass Block Installation Mortar Mix

5. Install The First Row

A. Place two glass blocks in the sill channel, sliding one block into the right jamb and one block into the left jamb. Make sure the blocks are seated in the channels.

B. Install the next glass block:

  • Apply 3/8″ to 1/2″ of mortar to the edge of the next block.
  • Place the block in the channel with the mortar facing a previously installed block.
  • As you install the block, insert a “REGULAR” spacer with the cross arm down where the two blocks meet.
  • Push the block firmly in place, forming a 1/4″ mortar joint. Make sure the joint is completely filled with mortar.

C. Install the remaining blocks in the first row in the same manner.

  • Apply 3/8″ to 1/2″ of mortar to both edges of the last block installed in the row.
  • Be sure to insert “REGULAR” spacers with the cross arm down, where two blocks meet.
  • Push the blocks firmly in place, forming 1/4″ mortar joints. Make sure the joints are completely filled with mortar

D. Remove excess mortar with a polyfoam brush, and fill any voids on both sides of the panel.

6. Install The Remaining Rows

A. Apply a 3/8″ to 1/2″ mortar bed on top of the first row.

B. Place a “FLAT” spacer on top of the first and last block of the previous row where they meet the side channels.

C. Set the first block and last block of the next row into the side channels on top of the “FLAT” spacers.

D. Install the remaining blocks in the row in the same manner as the first row.

  • Apply 3/8″ to 1/2″ of mortar to the edge of each block that meets a previous block. Apply mortar to both edges of the last block installed in the row.
  • Be sure to insert “REGULAR” spacers with the cross arm down, where two blocks meet.
  • Push the blocks firmly in place, forming 1/4″ mortar joints. Make sure the joints are completely filled with mortar.
  • Remove excess mortar with a polyfoam brush, and fill any voids on both sides of the panel.
  • Check periodically to ensure that the blocks are straight, level and plumb. Adjust as needed.

E. Repeat Steps 6A – 6D to install each row of block, except for the next to last row.

F. Install the next to last row of block using “H” spacers in place of “REGULAR” spacers. Insert “H” spacers and “FLAT” spacers as shown.

G. Lay a bed of mortar on top of the next to last row, installing “FLAT” spacers at each corner.

H. Install the last row of block starting with a block in each top corner, then work toward the middle. Be sure to apply mortar to both sides of the last block.

I. Press any mortar that has been forced out back into the joints using a polyfoam brush.

J. Remove all mortar from the glass block faces.

7. Finishing The Glass Block Window Installation

A. Twist off the spacer tabs on both sides of the panel.

B. With moderate pressure, run the striking tool over all the joints. It is best to strike all the horizontal joints first, then the vertical joints so the pattern is uniform. Fill any voids with mortar.

C. Use a damp sponge to remove the excess mortar from the glass block face, rinsing the sponge frequently. Do not be concerned about the dry film that remains on the blocks, it will be cleaned off later.

Glass Block Window Installation

D. Use a soft, dry cloth to remove the excess film. A common household plastic scouring pad can also be used.

E. Cut the expansion strip to a 1-1/2″ width and insert it between the top of the blocks and the frame.

F. Apply sealant to the back of the half-section of channel and install it between the expansion strip and frame. G. Apply glass block sealant around the perimeter to seal the glass block and channel. Also seal the top channel to the frame at the head.

Now that you have installed your very own glass block window, it’s time to enjoy all the joys glass block can bring!


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