Step 1
Close and lock the sash. Tape the heavy plastic over the inside of the window to prevent shards from spraying throughout the room. Clear the area around the outside of the window to ensure you have a clear space and solid footing. If you need to use a ladder, make sure it is solidly set.
Step 2
Put on your safety glasses. Chip the old putty out of the window frame all around the glass. Start at one spot on the frame and use the hammer and chisel to get under the putty in a parallel motion. The old putty should come out in chunks. Be sure to save the retention clips. Clean the small debris and dust out of the frame with the paintbrush.
Step 3
Spread a small bead of silicone sealer around the perimeter of the frame in such a way that the new glass will seat in the adhesive. Carefully press the glass into the silicone until it is flush against the inside of the metal frame. Some seepage is normal and may be cleaned up later. Install the retention clips in the frame. You should have at least one on each side.
Step 4
Prepare your glazing putty by emptying the contents of the container on a hard surface. Knead the mixture like dough until it reaches a uniform consistency. It should not be sticky. Take a ball of putty in the palm of your hand and push it into the channel surrounding the window. You want to fill the space completely. It is easier to push the putty in along the length of the side than it is to push it in at a right angle.
Step 5
Using your putty knife, form a triangle between the outer edge of the sash holding the glass and the inner edge of the sash that conceals the putty from the inside. This is the shape your finished putty should have. Move your knife at this angle smoothly from corner to corner. Catch the excess putty as it comes off the sash and use it to fill gaps. Make sure your corners are finished neatly and without gaps that will allow water to seep into the frame.
Step 6
Use the razor blade or paint scraper to gently clean the wet silicone from the inside of the window. Do not press too hard against the glass or you will ruin your work.