Fix a putty window

 In Glass, Renovating, Repairs

Fixing broken glass in your own widows is so easy it amazes me that more people don’t do it themselves. There are a couple of rules you need to follow with any window and as long as you follow these simple rules it’s easy as pie, and given the price some companies charge to fix a broken window it makes a lot of financial sense too, at the end of this post you will know how to fix a putty window.

The golden rules of glazing

The first rule applies to a lot of DIY projects – measure twice cut once. This is especially important with glass as unfortunately you can’t easily cut a few millimetres off glass and it doesn’t like to bend, whether your cutting it yourself or ordering it from a glass shop, always check it twice.

The next golden rule of glazing is don’t let glass touch metal, if you’re repairing a timber window then the glass can be placed straight on the wood, but there should always be something between the glass and any metal on the frame, you could use rubber gasket, silicone, double sided tape, putty or plastic bead.

Another important thing is to make sure you are putting the right glass in the window, this varies from country to country, if you live in Australia check out my choosing the right glass page, if not check your local building standards.

OK so you have a broken timber window (I’ll explain other types of windows in future posts) the first thing you want to do is put on your safety gear, check out my handling glass safely page, then you want to clear away any broken shards from the area. When removing broken glass from a window always start from the top, being very careful not to accidentally touch any sharp bits, stay calm and focused while doing this, it’s a moment of panic that will cut you. If you have a glass cutter it’s helpful to make cuts in the broken glass, making small triangles and removing one piece at a time. For stubborn pieces lightly tap them with a hammer whilst holding the piece that you want to remove in your gloves. Never force a piece free, that’s a sure fire way to get cut.

Once you have removed all the broken glass, unless you’re very lucky, there will be a lot of putty still left in the rebate, professional glaziers use a special tool to remove this called a hacking knife, for the DIY-er an old chisel will do the job. Lightly tap the chisel with your hammer being careful to only remove the putty and not gauging into the wood. There will also be small diamond shaped metal glazing sprigs or small nails in the side rebate, these hold the glass in place, remove them completely as well.

So you should now have a clean rebate. If you haven’t already, measure the size for your glass and either cut it or order it. Make sure you check three points when you measure, for both the height and the width, some windows will be bowed or made out of square (in other words crooked!), make sure your glass is going to fit.

There are two ways you can go from here to complete the job, you can use back putty or silicone. If you want a nice, clean paint line then back putty is the way to go, but if you just want the quick and easy way then use silicone.

  1. Using Back Putty – You should use a linseed oil putty for windows, it’s designed for this purpose and is easier to work with. Knead your putty for a few minutes before starting, it will soften it up and make it easier to work with, roll the putty into long worms about the thickness of a pencil and push it firmly into the rebate, keep going until the whole rebate is filled.
  2. Using Silicone – Before you open the tube of glazing silicone, make sure the surface is as dust free as possible, then open the and lay a fine bead of silicone around the whole rebate making sure there are no gaps.

Once you’ve done this step, push the glass into the rebate (and onto the silicone or putty). If you’re using putty, carefully push until you have about 2mm of putty between the glass and frame the excess should ooze out to be cut off later.

Glaziers will use a sprig gun now to secure the glass but I’m guessing you may not have one, so what you’ll need are some small nails, carefully nail them into the side of the rebate – they should be hard up to the glass, you can use your chisel to tap them right in, hold the face of the chisel on the glass and tap one side with your hammer and the other side on the nail, this is the one time that metal can touch glass, you should put a nail every 200mm.

Now you’re ready to “putty up”. This is a bit of a practiced art for those in the professional glazing game, I’ve seen some guys from England that could putty a window in one minute flat, blind folded whilst humming God Save the Queen, standing on one leg! Now that’s great if you’re making a living doing it, but all you want is a window that doesn’t fall out and looks the same as all your other windows – right?

So – knead your putty for a few minutes before starting and then push the putty into the rebate so you can “face it off” with your putty knife (I’ll get to this in a second).  You can roll it into a snake or hold it with one hand and push it in with your other, you just need to make sure the whole rebate is filled, next grab your putty knife – if you want to, hold it by the side of the blade – start at one corner, press your putty knife into the putty, cutting the putty about 1mm in from the inside rebate and on the outside edge of the rebate and you want to drag the face of the knife down the putty.

The corner of the blade will cut the putty on the glass and the face of your putty knife will smooth the putty, remove any excess putty. Continue doing this until all sides are smooth, don’t worry too much about the corners they can be neatened up at the end, by starting in the corner and blending back into the finished section.

When you have “faced off” the whole front you can cut away all your back putty excess, if you used it.

There you go – you’re done, it’s not easy to get a perfect edge on putty but you should be able to get a neat enough job, I have seen some professional glaziers that are very messy with putty. The secret is to know when to stop playing with it. I hope this has been helpful and I’m happy to answer any questions you may have just add a comment below and I’ll get back to you.

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