How to Build a Window Using Glass Blocks

Windows with Stone or Masonry Framing

• 1

  Measure the width and height of the window opening before removing the old window from the structure. Purchase glass blocks in the size and quantity needed to fit the window opening, and allow for 1/4-inch mortar joints between blocks.

• 2

  Remove the existing window, its frame and all the nails with a pry bar. Take off any stray mortar left behind from removing the existing windows. Knock off any high spots with a hammer and chisel, and try to create as level of a surface as possible on the masonry window frame.

• 3

  Apply a bed of mortar to the basement window opening. Level the mortar bed with a trowel.

• 4

  Put mortar on the side of the window frame that will receive the first glass block. The mortar application is often referred to as buttering. Apply mortar to one vertical surface of the glass block as well.

• 5

  Set the glass block into the mortar on the bottom and up the side of the masonry window frame. Orient the block so the unmortared vertical side is against the edge of the window and the mortared vertical side is facing the spot where the next block will be installed. Insert plastic spacers at the top corner between the block and the window frame and between the first and second blocks.

• 6

  Continue buttering one vertical side of the glass blocks as you set them in the window frame, putting plastic spacers between them, until you reach the end of the first row.

• 7

  Put down another bed of mortar, this time on top of the first row of blocks. Ensure the mortar is 1/4 inch thick; use plastic spacers if desired, to achieve an even line of mortar.

• 8

  Continue laying blocks one by one, with plastic spacers, until each row is complete, then lay down a bed of mortar on top of that row for the following row to set on. Carefully insert a bed of mortar on the top of the final row of glass blocks, using a small putty knife to ensure the mortar completely seals off the window opening.

• 9

  Allow the mortar to set up for about two hours, then use a mortar striking tool to go over the mortar joints. This will give a clean and more professional look to the window.

• 10

  Clean spilled or slopped mortar off the glass blocks with a damp, soft cloth.

Windows with Wood-Frame Opening

• 11

  Measure the width and height of the window opening before removing the old window from the structure. Purchase glass blocks in the size and quantity needed to fit the window opening, and allow for 1/4-inch mortar joints between blocks.

• 12

  Add a coat of wood preservative to the wood frame rough-in for the window before installing the glass blocks.

• 13

  Position a glass block in the lower corner of the window frame. Tuck an L-shaped spacer at the top corner, where the block joins the wall. Apply mortar to the vertical side of the block that faces away from the window frame. Do not apply mortar directly to the wood of wood-frame window openings; apply mortar only between the glass blocks. The area between the wood-frame window opening and the glass blocks will be sealed with silicone caulk and wood trim later.

• 14

  Apply mortar to the vertical side of a second glass block and place it against the first block, with the unmortared side butting up against the first block. Ensure that the mortar joint is about 1/4 inch wide by using a plastic spacer between the two blocks. Continue laying blocks to complete the first row.

• 15

  Put down a bed of mortar on top of the first row of blocks. Continue setting the blocks one by one, the same way you did in the first row. Repeat for the remaining rows until the window is complete.

• 16

  Use a striking tool on the mortar after it has hardened for approximately two hours. Run the tool over the mortar joints; it will clean up the appearance and create a more professional looking job. Wipe off excess mortar on the glass using a soft cloth.

• 17

  Frame the window opening with framing trim so it overlaps the window glass by at least 1/2 inch. Put the trim on both inside and outside of the window.

• 18

  Put a bead of silicone caulk around the edge of the window, wherever the glass meets the wood trim, both indoors and outdoors.