Building Glass Block Windows

Popularized during the 1950s by architect Frank Lloyd Wright, glass block windows primarily take the place of traditional casement or double-hung windows in bathrooms or saunas where privacy is important but natural lighting is also a requirement. For those wanting glass block windows without a lot of work, custom sizes are available, already assembled from glass masons. You may also order prefabricated windows for easy installation. For the handy do-it-yourselfer, a few guidelines will put you on the path to building your own glass block window to suit your own style.

Glass blocks
Glass mortar
Reinforcement wire
Spacers
Masonry trowel
Silicone caulking
Rubber mallet
Carpenter’s level
Redwood or cedar window frame

Instructions

- 1
  Ensure that you have the correct wood for the window frame. Since mortar will come into contact with the wooden frame along the edge, it is imperative to choose a wood that withstands moisture, such as redwood or cedar. Treated wood is unsuitable for the frame since it has a tendency to move and warp.
- 2
  Determine the window size by adding the size of blocks to the width of the mortar joints. Glass blocks come in various sizes but 8 inch by 8 inch is standard. Allow ¼ inch between each block for a mortar joint. Measure both horizontally and vertically. For instance, if you want to lay five blocks horizontally and five blocks vertically, you would add the block sizes and the mortar spaces and come up with 42 ½ inches (5 blocks plus 6 mortar joints).
- 3
  Prepare the mortar as directed by the manufacturer and apply an even layer to the bottom frame of the window, spreading it a little more than ¼-inch thick. Since you will push the blocks slightly into the mortar, you need a little more than ¼ inch. (See Resources below).
- 4
  
  Place the glass blocks, starting from one edge and put a little bit of mortar on one side. Put the first block with the mortar side against the window frame and push it into place. You need enough mortar on the block to make a ¼-inch joint.
- 5
  Put a block spacer on the top and the bottom open edge of the glass block and place another block in the same manner you did the first. This time, the mortar side will fit alongside the block you just placed. Press and slide the block into place. The spacers will keep the two blocks 1/4-inch apart and the mortar will fill the space in-between. Repeat this process for all the blocks in the bottom row. Work quickly but accurately.
- 6
  Level the first row using a carpenter’s level along the top of the glass blocks. Wipe excess mortar from the front and the back of the glass blocks. It’s handy to have an assistant standing on the outside for this step. Be careful when wiping off the excess mortar—it will scratch the glass if you press too hard.
- 7
  
  Lay reinforcement mesh, cut ½ inch narrower than the width of your blocks, on top of the first row. Cover the mesh with a layer of mortar and begin laying the next row just as you did the first. Repeat for all the rows, using spacers between the sides and tops of the blocks to maintain even joints.
- 8
  Remove the spacers when the mortar is set. They will slip right out. Fill in the gaps with a bit more mortar and smooth it out. Apply an even line of silicone caulking around all edges of the window, in the crease between the frame and the glass blocks.

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Windows