Most of the clients I visit think that having a broken or fogged double glazing unit (glass), it is necessary to replace the entire frame. Unless the frame itself was damaged in theft or by accident, the glass can be replaced without installing a new frame.

Glazing system identification:

The first thing to do is identify whether 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 new windows are internally glazed.

Withdraw the accounts in the windows with internal accounts:

Insert a stiff putty knife into the joint 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 cord from the frame. Remove all the beads one at a time and the double glazing unit should be free to be removed and replaced.

Remove beads on windows with external flange:

There are a few different glazing systems on windows with external glazing. The most common is the internal gasket or the rear wedge system. The rubber gasket on the inside of the window must be removed in order to remove the outer beads. To do this, take a stiff putty knife and press it into the rubber on the inside of the window and pull it out. Then follow the instructions to remove the accounts above. Make a note of the 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 fabrication and then the double glazing unit is pressed, allowing the outer cords to lock into place. Use a Stanley knife / box cutter to cut the tape. Keep the knife flat against the glass to avoid cutting the frame. Cut the entire area with masking tape and you should be able to poke the putty knife in and slowly lift the glass unit. 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 one that does not have a 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. One caveat with this type of frame, and some of the others. Some external glazed frames have glass locks installed. Glass padlocks are right-angle pieces of metal that are inserted into special retaining clips attached to the frame. If you remove the beads and see these metal clips, call a glazier as these clips can be very difficult to remove without the proper tools.

Double glazing unit measurement:

After removing the double glazing unit, it is advisable to take it to your local glass merchant to have it measured and checked for any special coatings that the glass may have. If the double glazing unit was sitting on plastic packers when you removed it, take them with you and ask the glass merchant if they are the right packers for the job, if not, get the correct packers. This is very important as the cause of most double glazing unit failures (mist / condensation between the panes) is that they have not been placed in the correct packers. If your window is glazed with security tape, you will need to purchase new double-sided security tape.

Replacing a double glazed unit with internal glazing:

Make sure the unit is square to the frame and that you have it positioned on its two packers. First, attach the two shorter beads by tapping them with a nylon mallet. Then place the two longest beads in the same way. You may need to push one end of the bead into position and bend the bead to poke the other end.

Retrofit of a double glazed unit with external glazing:

Back Gasket System – Attach the glass and beads as described above and then push the rubber gasket into the frame on the inside of the window. If the rubbers have shrunk, you can gently stretch them, then stretch them and reattach them with a small bead of glue at each corner to prevent them from shrinking again.

Security Tape System – Attach the new tape to your window frame, being careful to keep it aligned with the edge of the frame. Remove the cover and spray the tape with glass cleaner. This will allow you to move and align the double glazing unit. The glass 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. Place the glass and beads as described above.

One word of caution: some externally glazed frames have glass locks installed. Glass padlocks are right-angle pieces of metal that are inserted into special retaining clips attached to the frame. If you remove the beads and see these metal clips, call a glazier as these clips can be very difficult to remove without the proper tools.

If you are not sure what system you have or are not secure enough to continue the work, call a glazier. In the long run, it will be cheaper to get someone who knows what they are doing than to destroy your windows.