How to Install a Glass Block Window in New Construction

Glass block windows allow light in without sacrificing privacy.

Adding a glass block window to an exterior wall allows light to enter the space without privacy leaving it. Perfect for bathroom and bedroom applications, a glass block window offers an almost unlimited range of sizes and shape options with either square or rectangular available. By following the basic method for proper installation, the finished window will provide increased sunlight and an attractive detail to any room.

Note that glass block panels are restricted to nonload-bearing use, and the structural framing of the opening must adhere to code requirements for the planned opening. It is recommended that you consult your local building department to insure compliance with governing regulations.

Things You'll Need

• Tape measure
• Builders level
• Framing square
• Hammer
• 8d sinker or box nails
• 3/4-by-2-inch boards
• Utility knife
• Staple gun
• 15 pounds black builders paper
• Glass blocks
• Glass block spacer clips
• Glass block reinforcing bars or "ladders"
• Glass block mortar
• Masonry trowel
• Metal panel anchor straps
• Sponge
• Small bucket
• Caulking gun
• Tube of silicon caulk
• Clean cotton rags

Instructions

1. Do a preliminary inspection of the rough opening for the new glass block window. Check each corner with a framing square and use a builder's level to determine that the sill is level.

2. Install a continuous 3/4-by-2-inch wood frame for the opening, positioning the pieces flat against the perimeter framing and centered between the inside and outside faces of the wall. The glass block units will straddle this frame and be raised to create the first mortar gap against the window frame. This wood frame also provides a lateral security for the window.

3. Wrap the perimeter of the window opening with 15 pounds of builder's paper and attach with a staple gun. The paper should fit tightly against the framing and follow the contour of the frame installed in Step 2. This protects the wood framing from moisture.

4. Mix the glass block mortar in a small bucket, following the manufacturer's instruction. Use a masonry trowel to spread a layer of mortar across the full length of the sill of the opening. The mortar should be sufficient to set the glass block units and squeeze out evenly on both sides of the block.

5. Set the first row, or "course," of glass block by applying a layer of mortar to the frame side of the first block, placing in the lower corner and pushing it against the vertical frame on that side. Position a plastic, glass-block spacer clip at each block, then apply a layer of mortar on the side of the next block as it is pressed into place next to the previous block. When the first course is complete, ensure the glass blocks are straight, centered in the opening and level across the course. Spacing between each block and between the blocks and the perimeter frame should be even and consistent.

6. Use the trowel to collect the excess mortar that squeezed out and return to mix bucket. Use a wet sponge or dry cotton rag to wipe any spattered mortar from the glass block faces.

7. Bend a length of panel anchor into an "L" shape, with the short length about 3 inches. Nail the anchor to the side frame, keeping the short length parallel to the bottom of the window and extended onto the top of the first glass block in the course. Repeat on the opposite side of the opening.

8. Lay a length of glass-block reinforcing bars, or "ladders," across the top of the first course of installed glass block. Ladders should be horizontally continuous across the opening and should lap about 2 inches when multiple pieces are used. Repeat this step at every third course of glass block.

9. Spread a layer of mortar on top of the first course of glass blocks and the reinforcing ladders. Repeat Steps 5 through 8 to install the remaining courses of glass block.

10. Final cleanup of mortar and the glass blocks should be done when all the glass block units have been installed and checked for plumb and level. Check all mortar joints for evenness and consistency. Joints can be smoothed using a damp sponge. Allow mortar to cure for 24 to 48 hours before applying any wall finish or trim to the window assembly.

Tips & Warnings

• The light haze left on the glass block faces by the wet mortar can be cleaned with a dry cotton rag after mortar has cured.

• Run a solid bead of silicon caulking around the perimeter of the window panel prior to installing the wall finish or trim to the window frame.

References

• YouTube: How To Install Glass Block