Things my father taught me

 I can remember so many things my dad taught me, from how to hold a pencil, to fixing a petrol lawnmower, and even how to listen to classical music. The most dramatic of these "lessons" was when I was in my early teens and I had hit a cricket ball through one of the large windows (I was absolutely hopeless at cricket and most other ball games, so this was an accident waiting to happen!) My dad insisted that I should replace the glass, so he set up a deckchair outside and proceeded to instruct me.

The first step was to remove all the broken glass. My dad was excellent at thinking beyond the task at hand, and suggested I use some old painting drop-cloths on both the inside of the room and the flowerbed directly outside to catch the glass splinters and chips of paint and putty. This is definitely a job for leather gloves - the tiny splinters of glass can pierce through even quite thick gardening gloves. This gave me an early appreciation for why construction workers prefer to work without protective gear, as it is hot and uncomfortable, and in the case of the bulky gloves, destroyed all dexterity.

Removing the old glass was quite a mission as the putty had hardened over the years, so took quite a bit of effort with a scraper to clean the steel frame. Once this was done, I needed to measure the window frame. Even though all the windows in our house were "standard steel frame" with millimetre-accurate dimensions in the catalogue, the manufacturing is not always 100% accurate because the jigs to hold the horizontal and vertical members are supposed to be checked at regular intervals throughout the day, but the factories do not always stick to this regime. The first step was to check if all the internal corners were square, using my dad's adjustable set-square which I still own and use. Fortunately, they were pretty good, even though the opening was half a metre wide and one-and-a-half metres high, nearly as tall as myself. 

Clearing out all the old glass taught me exactly where to measure, and my dad advised me to subtract 3mm to the horizontal and vertical dimensions. This is to allow the glass to expand and contract, as this happens at a different rate to the expansion of the steel frame. If it is an exact fit, the glass could crack or even be forced to pop out of the frame, a scary thought given that this was a window to my own bedroom! 

We then set off to the hardware store to get the new glass and putty. The store owner was very helpful in advising on how much putty to get: any leftover putty will harden over a couple of months, and is quite a mission to work back to full plasticity, using smelly linseed oil and much manipulation. The putty from the store was still quite soft, but still needed a bit of work to be able to roll it into long sausages.

With steel frames, it is important to put in "back putty" so that the glass does not sit hard up against the steel. This needs quite a thin roll of putty all the way round the sides and top of the frame, and a slightly thicker roll at the bottom that you need to press into an L shape so that the glass can sit on putty and not directly on the frame. All this putty work can be done with bare hands, although some very thin surgical gloves are better, as the putty is made of lead. Whatever you do, though, be sure to wash your hands thoroughly with soap as soon as you are finished to avoid lead poisoning.

Then comes the scary part with such a tall pane - setting the glass in place. This was definitely a job for the leather gloves, as the glass needed to be picked up by the sides and gently lowered into place on the bottom roll of putty. The precise measurements earlier on in the job really pay off here - the glass should fit comfortably all the way round, but without any gaps. Once the glass has been lifted into place, I then needed to press it into place, working top to bottom and side to side evenly around the edge to make sure the back putty was an even thickness of about 2mm. Some of this back putty will bulge upwards as you apply pressure, but this can be trimmed later and is a good sign that you have done that step well. 

The front putty is what will be the most noticeable, and is often the giveaway of an inept DIY job if it is not done properly. The most efficient way to do this is to make a roll of putty about 3cm in diameter (the exact size will depend on the thickness of the frame and the depth of the back putty, so the first few pieces may be a bit of trial and error). First, push a piece of putty into the junction of glass and frame on all four sides to hold the glass in place. Then taking the roll, start to put this in place working along the top, and then alternating sides from top to bottom. Because the back putty is still very elastic, you don't want to put too much pressure on one side, as the glass could pop out. 

Once I had putty all the way round it was time for the test of my skill and patience. For all that I was getting entirely "deck chair instruction", my dad could be quite the perfectionist, after years as an architect of "snagging" builders' work. The only way to achieve a professional finish is to use the correct tool - a putty knife - as this has exactly the right balance of flexibility and rigidity. Holding the putty knife at 45° to the glass, I had to try to push the putty into place to meet the edge of the steel frame. In some places, I had too much putty, so I had to use the knife to cut some away. Where my roll of putty was too thin, it was much more of a mission to add more, and would not have been so robust, so my dad made me remove that section and re-work the putty into a thicker roll. Where horizontal meets vertical is the real challenge of patience, as one wants a neat mitre joint of the putty, and this took me several attempts.

Then was the time to trim off the excess back putty on the other side, a very easy task in comparison with the front. By this point, the glass was covered in fingerprints and putty smears, so I was instructed to wash the glass very gently, so that I did not wreck all the careful work. My dad advised me to leave the putty for about a week to set a bit, before painting.

Re-glazing is one of the many construction jobs that looks so easy when done by an artisan, but the skill is to achieve absolute millimetre consistency. This affects not just the look of the final product, but also the integrity of the work, saving many hours and money to replace cracked putty during the life of the building.