Restore traditional single-pane windows

While the traditional single-glazed sash is becoming rare, there are still a lot of wood windows out there worth repairing. Single-glazed windows are popular in heritage homes, sheds, garages and cottages. Window panes need reglazing when there is obvious cracking, chipping, gapping or other deterioration of the putty, allowing water to migrate into the sash. If tapping on the glass produces a rattle, the pane is due for reglazing. Thankfully, the skills are not difficult to master.

It's best to work with the window in an upright, vertical position, just as it is installed in the jamb. Often you can reglaze a window in place or rig up a glazing easel. This set-up can be as simple as an appropriately sized sheet of plywood held upright at an angle by some triangular brackets. Screw a scrap of wood for a ledge to rest the sash on and clamp, or screw the easel to a sturdy work table.

Deglaze, before reglazing

Removing old putty is the most time-consuming and difficult part of the job, but there are a few tools and techniques to help. The best way to get glazing compound out of the rabbet is with a chisel at least 1" wide, and you have to keep it sharp.

Begin by holding the chisel perpendicularly to the glass and in line with the edge of the rabbet. With one hand, hold the tip of the chisel between your thumb and forefinger, with the bevel up, resting your hand against the sash, and apply pressure while pivoting the tip in a circular paring motion. Work along the rabbet, chipping out the putty, aiming for the seam between the putty and the glazing rabbet. Stop to resharpen the chisel when it stops cutting effectively.

Glazing points can be removed with a putty knife or chisel, by wiggling them out gently. Tiny brads often secure leaded panels and can be removed with needle-nose pliers.

After removing the glass, clean up the rabbet by scraping out any extra putty. Painting a prime coat of boiled linseed oil on the bare wood of the rabbet can help the putty adhere well without drying out. A coat of oil-based exterior primer also does the trick.

 

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.

 

 

Final finishing

Apply the layer of putty that seals out the weather. Use the same smearing technique, but this time, hold the putty in one hand and use a putty knife to squish it into the rabbet. You should have a sausage-shaped lump of putty going. Hold the end of the sausage up to the rabbet and use the tip of the knife to push a chunk into it. It doesn't have to be neat looking. What you're aiming for is good contact between the putty and the sash and glass. Don't be afraid to use lots of putty-you'll clean up the extra. Work along until you have the rabbet filled. Then, draw the knife along with one hand with the knife tilted at an angle, from the outside edge of the rabbet to the inside edge (on the other side of the glass), and apply pressure to the tip of the blade with the other hand. Excess putty will be pushed over the outside edge of the rabbet and onto the glass, leaving a nicely formed fillet-or at least it will after a few practice runs. The tricky part is making a nice, compound bevelled corner where the two lines of putty meet. There's no magic though. You simply give your knife a twist and shape the soft putty into the correct shape. It's forgiving stuff. You can go over it again to smooth it out if you've made an error.

Let the putty dry thoroughly before painting, waiting until it has cured hard, and ensure that the paint overlaps the putty bevel and goes onto the glass by 1„16" to seal the putty.