Plexiglas costs more to buy than glass. One of the biggest advantages of this thermoplastic is that, unlike glass, it doesn't shatter. It can crack, break and be scratched. But when a Plexiglas window pane is hit, it won't shatter. Working with Plexiglas is easy, especially when you replace a window with it.
Put on the safety goggles and the heavy gloves. If you can easily remove the window sash, carefully do so. Windows can be difficult to remove. Removing the sash isn't mandatory. You can replace a broken window pane while it's in the frame.
Remove the broken glass carefully. Move the shards back and forth to free them from the glazing compound.
Use a flathead screwdriver to carefully remove the glazing compound and the glazing points. Don't gouge or otherwise damage the sash frame. You may need to use the screwdriver like a chisel to remove rock-hard compound.
Paint any bare wood on the sash with a waterproof sealer. Read and follow the manufacturer's instructions to achieve the best results. Allow the sealer to dry thoroughly before you proceed to the next step.
Measure the pane to determine how large the Plexiglas needs to be. Measure from the edges of the grooves. Then, deduct 1/8th inch from the length and the width. Order the piece from a local hardware or home improvement store.
Use a putty knife to apply a thin coat of glazing compound in the grooves, all the way around the window pane. Then, remove the protective plastic from both sides of the Plexiglas. Lay the piece in the grooves and carefully press it down into the compound to make a good seal.
Install glazing points into place on all four sides of the pane. The points help hold the Plexiglas in place. Lay a glazing point flat on the Plexiglas near where you want to install it. With the point facing the wood, push it into place with a putty knife. Repeat this process until all four corners have points in them. Then, install more glazing points about 8-inches apart around the diameter.
Apply more glazing compound into the grooves all the way around the pane. Use the putty knife to smooth the compound out.