Glass block windows can be perfect for a number of installations. They let a lot of light into a space while being almost impossible to see through. This makes them perfect for bathroom or basement windows.
Step 1 - Design
Plan out your glass block window before you get started. Measure the opening that you have, and see how many blocks you can place into the window. Glass blocks come in several different sizes.
Step 2 - Base Framing
Most windows will have to be framed in. It is best to use a cement based board to do the outer rim of the window. This can be attached to wood framed openings using screws, or to block surfaces with a good grade of industrial cement. Industrial cements are available at any home store in caulking tubes, and are easily applied. If you do use screws, do not use drywall screws. Use decking grade screws.
The framing is necessary to keep any gap in between the block and the outside opening The gap should never exceed more than 1/4 of an inch on any side. A little bit of "wiggle room" is necessary though.
Make a box that will encompass the glass block out of 1x4 inch treated wood. This box frame should be 1/4 of an inch smaller than the framed in window opening on each side.
Attach the two sides and the bottom to each other using wood screws. Do not attach the top part of the frame at this time.
Set this onto a clear and clean layer of plastic on a flat floor.
Glass Block Installation
Using a small trowel, spread on a thin layer of mastic adhesive onto the bottom of the window frame. Place the first course of glass block into the frame. Each block should have mastic on the sides so that they will be glued together. Now add on another layer of mastic on top of the this layer.
Repeat this process for every course.
After installing the top course, screw the top part of the window frame into place. The frame must be left aside to dry for at least 24 hours.
Finishing the frame
Use a white caulk to edge around each glass block, including the edges next to the wood. Wipe the excess off with a good sponge or clean white cloth. This also needs to dry prior to installation. Any dried residue can be scraped off with a single edged razor blade.
Installing the glass block and frame
Apply a heavy bead of adhesive onto the window sill. Place the glass block frame into the opening. If you do not have a helper to keep the window from tilting outwards, you will have to place a board on the outside. Let the adhesive cure for 30 minutes.
Spray in the Window and Door foam sealant around the perimeter of the frame, from the inside. This will need to set up overnight
Trim off the excess foam that has expanded through the outside joints. The edges of the window frame can now be trimmed out using whatever type of wood trim you prefer. Caulk all of the joints, and then paint to match your wall color.