Detailed Instructions for removing Glass
It is very time consuming to remove existing glass intact to use it to secondary glaze another window. This is particularly true if it is 3 mm glass and if it has been well sealed. The following instructions will minimise the risk of glass breakage, but will not guarantee it. Generally, people take several hours to successfully remove the first pane of glass. They then try to take short cuts on later panes, until the start breaking the glass. They then take more care and are again successful.
It is important that gloves and safety glasses are worn at all times. The most critical thing to achieve success is a very thin blade to ease the glass from the window. A putty knife is the best that I have found. It has a thickness of around .1 mm. Caution should be used with this knife as the edges are very sharp and pushing against the edge will cause cuts. It is worth attaching a wooden handle to the blade.
Step 1. Removing the external beading
The window is normally held in place with a combination of wooden beading and hard sealant. The wooden beading can be removed using a sharpened screwdriver or chisel. This should be entered between the beading and the frame NOT between the beading and the glass. Gentle levering will generally get it to come off. It is recommended that you place a putty knife against the window frame to avoid damaging the frame. If you are careful, you may be able to reuse the beading later, but normally a new piece of 12 mm angled quad will be required.
Step 2. Removing the hard sealing
This is normally present at the base of the window and is harder to remove. Generally a hammer and chisel is required. Avoid having the chisel directly touching the glass. The best way is to gently tap the chisel between the cement and the frame and lever it out.
Step 3. Removing metal retainers
Often there are small diamond shaped bits of metal holding the window in place. They are approximately 3 mm in size and can be eased out with a chisel.
Step 4. Removing the silicon sealant on the outside
Most windows are held in place using silicone sealant. Firstly you should break the edge seal from the outside using a narrow bladed putty knife. This generally works well, provided the glass is not tight against the frame. If so, do not try to force the knife (photo).
Step 5. Add stops
Two wooden stops should be screwed in place so the window cannot fall out
Step 6. Removing the silicon sealant on the inside
This is the hardest part of the operation and most likely to cause cracking of the glass. Wear goggles and gloves and take your time. The most critical thing is not to rush it. Normally the seal at the top of the glass will be weakest and you can push the blade in several mm. Cracking normally occurs when the blade is pushed to the full depth, next to a place where the glass is still fully held. In general it is better to push the knife several mm in all along the side then return to do another couple of mm. It is good to use a knife that has been cut at 45 degrees on each side. This minimises the risk of cracking and is good for cleaning out the corners. You can use the shaped knife, pushing it in 5 mm all the way around then use the flat blade to push in 5 mm and even it all up.
Note: 3 mm glass is very difficult to remove and reuse - it will crack very easily. 4 mm glass is much easier to handle.
Step 7. Clean up the frame
It is important to remove all traces of the silicone. This can normally be done best by dragging a chisel or putty knife along the edge. Use a brush to remove all dust and debris. You can buy a scraper tool from Total Tools for around $60. This works extremely well.
Details on adding a double glazed unit
Details on adding secondary glazing