Restore traditional single-pane windows

Practise your puttying

The secret to working with glazing compound is to keep it warm and flexible. It needs kneading to soften up and remain workable. In warm summer weather, keeping a ball moving in your hand should keep it flexible. Where leaded glass panels are being set, or where the sash is going to get a dark paint colour, you can colour the putty with universal colourants from a paint store, so that a telltale white line of putty won’t be visible from the inside of the window. You can use a regular 1″ flexible putty knife, but a glazier’s supply shop will have stiffer, square-edged knives to choose from.

You need to first bed the glass in a thin layer of putty that you apply to the rabbet. I find that the often-recommended practice of rolling up a thin snake of putty to place in the rabbet is too difficult and time-consuming. A better technique to learn is how to smear small dollops of putty into the rabbet with your thumb, while you hold a wad of putty in one hand. Move along, all around the rabbet, until you’ve made a consistently thin layer to bed the glass in. It won’t be smooth. It should look more like you’ve pinched the decorative edge of a pie crust. Press the glass into place firmly, smooshing out the extra putty, until the glass is evenly set in the rabbet. A quick scoring pass with a putty knife will clean things up.

Now you need to set some glazing points to hold the glass in place. The points will be on the outside face, where the next layer of putty has to go, so ensure they are seated well-they should not interfere when you shape the compound.