How to repair a window
Cracked or broken glass in windows or doors can be very dangerous, especially if you have small children or pets. You could be compromising the security of your home, and the glass won't be weatherproof any more. If you can't make a full repair straight away, try at least to make a temporary repair and ensure the area is safe.
If you need to replace glass in an upstairs window, work from a scaffold tower rather than a ladder and avoid working on a windy day. It's also best to carry the panes on edge to stop them bending and to wear protective gloves while you're doing the job. And remember that to handle large pieces of glass safely, you'll need someone to help you.
If security isn't a problem, you can use polythene sheeting to make your window temporarily weatherproof. Remove the broken glass, spread the polythene across the gap and secure it with thin wooden battens nailed to the edges of the frame.
If the glass is cracked rather than broken, you can seal it with waterproof glazing tape instead. But if it's an accessible exterior window that's been damaged, you'll definitely need a more secure repair.
Top tip - Weatherproof repair
If the weather is bad and you can't fully repair your window straight away, use silicone sealant to make your temporary repair weatherproof. Leave the broken glass in place and put silicone sealant around the edge of the pane. Cut a piece of board to fit, and press this into the silicone. Then run another bead of silicone around the gap between the board and the frame.
Put on some protective gloves and remove any loose pieces of glass.
Measure the space and cut a piece of thin hardboard or plywood to fit.
Fit the cut board into the frame and tap panel pins into the surrounding wood.
A glazier will be able to cut glass for you and advise on the best type for the window you're replacing. It's best to use safety glass if it's a large picture window, or a window that's within 800mm of the floor.
It's very important to dispose of broken glass safely. So wrap it in old newspaper, tape it up securely and label it clearly with the following: 'Danger - broken glass'.
Measuring pane size and thickness
It'll help to make sure you buy the right thickness if you take a piece of the broken glass with you, wrapped carefully in newspaper. If that isn't possible, measure the thickness of the pane to the nearest millimetre. You might not be able to find an exact match if the glass is old. If this is the case buy slightly thicker glass instead, as this will be safer. As a rough guide, you should use 3mm glass for very small panes, 4mm for windows up to 1 square metre, and 6mm for larger areas. Find the height and width of the area, measuring into the frame rebate on each side, and have your new glass cut to 3mm less than both the length and width measurements. You can check if the window is square by measuring the diagonals. If they differ by more than a couple of millimetres, make a cardboard template of the window pane and take it to the glazier to use as a guide.
Types of putty
You'll need about 500g of putty to fill a rebate about 4m in length. Use linseed oil, all-purpose or acrylic putty if you're glazing painted wooden frames. Brown putty works well in stained and varnished wooden frames. And for metal frames, use all-purpose, acrylic or butyl rubber-based putty.
Spread some newspaper on the floor around the window to make it easier for you to clear up afterwards, and put some sturdy footwear on. If your pane is only cracked, score it with a glass cutter about 25mm from the edge all the way round. Stick strips of adhesive tape across the cracks and scored lines, then tap each piece of glass free with a small hammer. The tape will hold the pieces safely together.
If the pane has smashed, remove the jagged pieces still stuck in the putty by gripping each one in turn and working it loose. Make sure you wear protective gloves and goggles when you're doing this. Work from the top down, and knock out the remaining glass by tapping it gently with a hammer.
Use a chisel or glazier's hacking knife and hammer to remove the old putty. Take out the panel pins as you go, using a pair of pincers.
Brush away any dust and seal the wood with primer paint.
Work from outside and clean any debris from the rebate in the frame with a brush or an old screwdriver. Rest the pane on a pad of newspaper away from where you're working - but don't stand it on a hard surface like concrete, as it could crack. Linseed oil putty can be messy to work with, so wet your hands to prevent excessive sticking. And if you need to, roll the putty on newspaper or card to remove some of the oil.
Knead the putty until it's soft and supple. Then take a palm-sized ball and squeeze a continuous band into the rebate, using your thumb to press it into place. It should be about 3mm thick all around the window.
Put some gloves on, sit the new pane of glass into the bottom edge of the frame and gently push it into place. Put gentle pressure around the edges of the glass - not in the middle, especially if you're working with a large pane, as it may break. Let the glass squeeze the putty until you've got about a 2mm bed of putty behind it.
Fix the glass in place by tapping in glazing panel pins at 200mm intervals with a small hammer. They should lie flat against the surface of the glass and stick out 5mm from the frame. Take away any extra putty from the other side of the glass with a putty knife.
Put more putty into the rebate around the window, using your thumb to push it well into the edge. Then take a putty knife and smooth the putty into a neat fillet running at an angle of 45 degrees. Make sure you cover the heads of the panel pins and line up with the putty on the inside of the window. Next, wet your putty knife to get a really smooth finish and a clean angle at the corners. It's wise to let the putty harden for about two weeks before you paint. And when you start painting the frame, overlap paint from the new putty onto the glass by about 3mm to stop water from getting through.
To mend a broken pane in a beaded casement window, you'll need to take out and replace the wooden beads. This is a bit complicated, but not too difficult.
As you remove the beads, lay them out carefully so you can put them back in the same positions.
Take out the broken glass (remember to wear protective gloves and goggles when you're doing this).
Once you've safely cleared the glass away, scrape out the old putty from the rebates with a hacking knife or old chisel. Brush away any dust and paint the rebate with wood primer or primer/undercoat. Then let it dry thoroughly.
Measure up the new pane. You can do this by taking the horizontal and vertical dimensions to the inside of the rebates, and reducing the measurements by 3mm to allow some tolerance when fitting.
Knead a palm-sized ball of putty until it's soft and supple. Press it into the rebate with your thumb (it should be about 3mm thick all round). Then put your new pane in - you should slot it into the bottom, rebate first. Press the glass gently around the edges (not in the middle) until you've got a 2mm bed of putty behind it.
Put another band of softened putty around the pane - making certain you press it well into the edges.
Then press the casement beads into the putty in the same positions as they were before. Fit the top bead first, followed by the bottom, then the sides. Next, tap panel pins into the existing holes.
Complete the job by cleaning away the excess putty on both sides of the glass with a putty knife, and repainting the woodwork.
There are lots of wood repair compounds on the market that'll help you make a good repair to a rotten window sill. Remember that if your sill is stained or varnished rather than painted, the repair will stay visible unless the filler is the same colour as the wood.
Start by removing all the rotten wood using an old chisel or narrow-bladed scraper. Dig into the frame until you reach firm, sound wood.
Knead the repair compound until it's mixed through. Make sure you follow the manufacturer's instructions and wear protective gloves.
Press the compound into the damaged area with a narrow bladed scraper, and smooth the surface to follow the sill's profile.
If there are gaps between the window frame and the wall, seal them with a waterproof frame sealant. Then finish the job by repainting or varnishing the window and frame.
Galvanised metal window frames are bound to get rusty sooner or later. And while most paints slow down the rate of corrosion, they can't stop it altogether. When you repaint the frame, use a good-quality primer and make sure it goes into any crevices and awkward areas. Pay special attention to the outer corners and edges.
Use a scraper to remove loose and flaking paint.
Then go over the metalwork with a wire brush until you've removed all loose paint or rust.
Smooth the whole surface with medium-grade abrasive paper, focusing on the rough edges. Brush the dust off.
Paint the frame with a rust remover and allow it to dry for the period advised on the tin. Next, paint the frame using a zinc-based metal primer.
Repaint the frame. Put an undercoat on first and then a top coat.