Most of the clients I visit think that when they have a cracked or fogged up double glazing (glass) unit, the entire frame needs to be replaced. Unless the frame was damaged in a theft or by accident, the glass can be replaced without installing a new frame.
Identification of the glazing system:
The first thing you need to do is identify if the framework has accounts externally or internally. This is done by looking at the beads where they meet the inside edge of the window frame and identifying if there is a seam there. Most of the new windows are internally glazed.
Removing trim from windows with inner trim:
Insert a stiff putty knife into the seam between the bead and the frame in the middle of the longest bead. You may need to push or tap the putty knife to separate the bead from the frame. Remove all the beads one by one and the double glazing unit should be free to remove and replace.
Removing trim on windows with external trim:
There are a few different glazing systems on externally glazed windows. The most common is the internal joint or back wedge system. It is necessary to remove the rubber gasket from the inside of the window in order to remove the external beads. To do this, take a stiff putty knife and press it against the rubber on the inside of the window and pull it out. Then follow the instructions to remove the accounts above. Take note of which way the board comes out.
The next most common external glazing system is double-sided security tape. The tape is placed on the window frame during manufacture and then the double glazing unit is pressed, allowing the external beads to be snapped into place. Use a Stanley Knife/Box Cutter to cut the tape. Hold the knife against the glass to avoid cutting into the frame. Cut around the taped area and you should be able to insert the putty knife and slowly lift the glass unit up. Once the glass has been removed, you can get a scraper and remove all the old tape from the window frame, being careful not to damage the frame. Then follow the instructions to remove the accounts above.
The third and least common type of glazing system is the type that has no gasket or tape on the inside of the window. The beads of this type of frame can be removed from the outside with a putty knife. A word of caution with this type of framework, and some of the others. Some frames with external glass have glass locks placed on them. Glass padlocks are right-angled pieces of metal that snap into special support clips attached to the frame. If you remove the beads and see these metal clips, please call a glazier, as these clips can be very difficult to remove without the proper tools.
Double Glazed Unit Measurement:
After removing the double glazing unit it is advisable to take it to your local glass dealer to have it measured and to check if there are any special coatings the glass may have. If the double-glazed unit was on plastic gaskets when you removed it, take these with you and ask your glass dealer if they are the correct gaskets for the job; if not, get the right packaging. This is very important as the cause of most double glazing unit failures (fog/condensation between the panes) is that they have not been fitted with the correct shutters. If your window is glazed with security tape, you will need to purchase new double-sided security tape.
Refitting a double glazed unit with internal glazing:
Make sure the unit is square in the frame and you have it on its two packers. Attach the two shortest beads first by tapping lightly with a nylon mallet. Then attach the two longer beads in the same way. You may need to push one end of the bead into position and bend the bead to insert the other end.
Refitting a double glazed unit with external glazing:
Back Gasket System – Fit the glass and trim as described above then push the rubber gasket back into the frame on the inside of the window. If the rubber bands have shrunk, you can gently stretch and reattach them with a small bead of super glue in each corner to prevent further shrinkage.
Security Tape System – Attach the new tape to your window frame, taking care to keep it flush with the edge of the frame. Remove the cover and spray the tape with window cleaner. This will allow you to move and align the double glazed unit. The window cleaner will evaporate in a couple of hours, leaving you with a double-glazed unit that can only be removed by cutting it from the inside. Lay out the glass and beads as described above.
A word of caution: some frames with external glass have glass locks placed on them. Glass padlocks are right-angled pieces of metal that snap into special support clips attached to the frame. If you remove the beads and see these metal clips, please call a glazier, as these clips can be very difficult to remove without the proper tools.
If you are not sure which system you have or are not confident enough to continue with the job, call a glazier. It will be cheaper in the long run to get someone who knows what he is doing than to destroy your windows.