METHODS OF FITTING.
There have been three methods of fitting windows used in the cathedral.
1. Stone set windows.
This is a traditional extensively used method of fitting leaded or stained glass into masonry from the inside. There is a glazing groove in the reveal about 1 inch (25mm) square on the left hand side and a groove about ½ inch (12mm) square on the right hand side. The window is introduced into the left hand groove, the right hand side of the window just clears the reveal, after which the panel is straightened and shifted half an inch (12mm) to the right which is its final position. The window is then held in position by mortaring the inside of the grooves while the outside of the window is pressed firmly against the weather-sealing stone rebate. This method of fitting has been used extensively in the cathedral, including all the clerestory windows, all the upper aisle windows, and the “West” windows.
The mortar used should be a lime mortar. This mortar should be able to be raked out of the grooves with a kitchen fork.
We repeatedly tried the strength of this mortar with a hammer and stone chisel. (See window 28 photo 91). At every site the mortar which had been used was far too stiff and appeared to be the consistency of “brickies mortar”.
This poses a substantial problem for the removal of the windows. We anticipate that it would be futile and dusty trying to chip our way back through that mortar to the original groove. We anticipate that the external sacrificial border of the windows – incorporated into the design of the windows for such a contingency – would have to be broken and the windows removed by cutting the remaining leads. The borders would then have to be re-established using new matching materials in the sacrificial borders during the releading process.
Once the windows were removed the original masonry grooving would have to be re-established. This is usually done by using an angle grinder supported by a guide which would be needed to cut back the hard mortar to the original glazing groove. This is a slow, expensive and dusty undertaking.
There are many hundreds of lineal metres of stone grooving in the Cathedral that needs to be recut in this fashion. It would not need to be done if correct fitting conventions had been employed.
2. Ramped mortar setting.
The more complex shaped windows such as the octofoils (see window 17 photo 151) are set in ramped mortar. This is a traditional method of fitting windows with complex outlines. The window is constructed so that its outside dimensions are exactly the same