Preparation

• 1). Measure the window opening and determine the right size and number of glass blocks required to fill the space. Calculate the amount of framing material needed as well. The framing material should be at least the width of the glass blocks, usually either 3 inches or 4 inches.
  
  
• 2). Purchase the glass blocks, glass block mortar and spacers from the glass-block manufacturer as required. The exact materials may differ, depending on the glass block manufacturer's specifications. The treated wood framing material, silicone sealer and screws can be found at any local hardware store.
  
  
• 3). Remove the existing window and as much of the frame as necessary to fit the glass blocks and framing material into the opening.
  
  
• 4). Install the treated wood frame into the opening and secure it in place with screws. Make sure the frame is level, and if not, use masonry cement or wood shims to level it. If cement is used, let it dry thoroughly before continuing with the glass-block installation.
  
  
• 5). Prepare the spacers according to the manufacturer's instructions. Use tin snips to clip off the tabs for the spacers used at each corner, known as L spacers, and against the frame, known as T spacers.
  
  

Installation

• 1). Prepare the glass-block mortar according to the instructions on the container. Glass block is nonabsorbent so the mortar needs to be rather thick to stick correctly. The mortar should not slide off when the glass block is turned so the mortar is on a vertical side.
  
  
• 2). Spread a 1/2-inch layer of mortar on the bottom of the frame. Hold a glass block up to the corner and place an L spacer in the corner and a T spacer with the flat side along the bottom at the other end of the glass block.
  
  
• 3). Place a strip of expansion foam in place against the side of the frame. Set the block in place on the spacers and press it firmly against the expansion foam. This foam allows the glass-block panel to expand and contract to relieve stress from changes in temperature. Do not spread mortar along the side of the block that touches the foam.
  
  
• 4). Spread a 3/8- to 1/2-inch thick strip of mortar along one side of another block and slip it into place with the mortar against the block that is already in place. Position a T spacer on the bottom of the seam before setting the block in place and an unmodified spacer at the top once the block is in place.
  
  
• 5). Repeat Step 4 until all the blocks are in place but the last. Repeat Step 3 to fit the corner block and expansion foam into place against the opposite side. This block will need mortar spread on the side opposite the frame to connect it to the glass-block row. The T spacers are used only against the frame, the L spacers in the corners and the unmodified spacers where four glass blocks join together.
  
  
• 6). Run the polyfoam brush along the seams to clean up excess mortar and fill any holes.
  
  
• 7). Spread a 3/8- to 1/2-inch thick line of mortar along the top of the row. Take care not to get mortar on top of the spacers, or the blocks will not fit correctly. Make sure the row is level both vertically and horizontally.
  
  
• 8). Repeat Steps 3 through 7 to complete the glass block panel, except for the foam, which is already in place. Do not spread mortar along the top of the top row of blocks. Check periodically to make sure everything is still level.
  
  
• 9). Place a piece of expansion foam along the top row of blocks.
  
  

Finishing

• 1). Leave the mortar to set for about an hour, then break the tabs off the spacers on both sides of the window.
  
  
• 2). Clean any stray mortar from the glass blocks with a damp sponge, rinsing the sponge often. Do not let the mortar dry before cleaning it as it is much harder to wipe off once it dries.
  
  
• 3). Run the striking tool along all the horizontal seams then all the vertical seams to produce a smooth, concave seam free of gaps.
  
  
• 4). Use the silicone sealer along all the seams between the glass block and the frame and between the frame and the basement wall.
  
  
• 5). Clean any remaining film from the cement with a soft, dry cloth once the mortar has set and dried fully. Do not use any abrasive agents to clean the glass block, or it will get scratched.