Repairing a broken door glass pane isn't a difficult do-it-yourself job if you follow some simple steps carefully and have all the equipment you need on hand before you start. It can easily be done by one person.
Before you begin, check with your local home improvement center about the restrictions in your area about glass in the front and rear doors of your home. Many areas have safety glass requirements for this. Have the replacement glass cut according to these requirements.
If the glass you are replacing is broken and pieces are missing, put on your gloves and safety goggles and simply remove and discard the glass. If it is cracked, you need to use the masking tape to tape in a 'criss-cross' manner across the cracked pane. This will help to keep the glass from flying everyplace when you crack it. Using the hammer, tap the glass until it breaks, then remove all the broken pieces and discard. Keep the area swept up of glass chards and splinters. It's also important to keep kids and pets out of the area when working with broken glass.
Using the putty knife, scrape away all glazing putty, old glaziers points, and excess paint or varnish. If there is a wooden frame surrounding the glass pane, you will need to remove all the wood strips, called mullions, on one side of the pane. You will find it easier to remove the long sides of the wood frame first, then the shorter ones. You may need to use a bit of pressure to do this if the frame has a lot of paint or varnish on it, but be careful not to break them. Use the putty knife to scrape old stain, varnish, or paint off to create a smooth surface.
Take a very small amount of the window putty and work it in your hands until it becomes soft and easily pliable, just like working with modeling clay. Put a thin amount all around the flat side of the remaining frame and smooth a bit with your fingers or putty knife. This will act as a bit of adhesive to hold the glass in place during the next step.
Insert the new glass pane into the opening and put flush against the wooden strips and use the glazier's points to hold it in place. Push the points in securely with the putty knife, using at least two per side. They must be completely flush with the inside of the frame.
Reinstall the wooden strips that you removed and tap into place. If you need to use new nails, use very small brad nails.
The above techniques are for replacing one or more panes in a multi-pane door or window. If you are replacing one large glass piece, remove the door and place it on a flat surface as it will be much easier to work within that position.