The commonest problems with windows are the sticking of moving parts, damage caused by rot and cracked or broken glass. Where hinged casements or sliding sashes stick, the trouble may be caused by the accumulation of paint on the meeting surfaces, and it can often be cured by stripping back to bare wood and repainting. If more clearance is needed, the sticking edge can be planed to remove a little more wood. Another cause of sticking with both types of window is sagging — where the joints in the casement or sash open up and allow it to sag out of square. You may be able to correct the sagging in situ by recessing L-shaped metal repair brackets into the surface at each corner of the sash or casement, covering them with wood filler and painting them; alternatively, you will have to remove it from the frame, square it up on your workbench and drive small glued hardwood wedges into the mortises at each joint to tighten it up. Take care not to overdo this, or you may crack the glass. Before replacing the sash or casement, check that the top and bottom edges are well painted; they are often left bare, and water can then penetrate, leading to rot.
Repairing rot damage
If rot damage is not extensive, you may be able to patch the damaged areas with wood filler after cutting away rotten wood. Where the casements or sashes show signs of extensive rot damage, you can replace rails or glazing beads with new mouldings, which are available from most timber merchants. This will involve careful cutting away of the old wood, and you may have to strip down the sash or casement completely. The alternative is to buy a complete replacement casement or sash if your window is a standard size, or otherwise to have one made for you. Rotten sills can be patched with new wood, jointed to the old with glue and wooden dowels to reinforce the repair. The window frames themselves can be patched on a small scale, and gaps between the wood and the masonry should be filled with non-setting mastic.
Replacing sash cords
One of the trickiest repairs is replacing the sash cords on sliding sash windows. When one breaks, you should always replace both cords at the same time; if you do not, the one you did not replace is sure to break in the near future.
Start by removing the staff beads with a chisel, and open up the pocket piece at each side of the window. Retrieve the weight from the side where the cord is broken, and wedge the inner sash up so you can pull the weight from the other side out through its pocket and cut it off its cord. Now you can lower the inner sash and lift it out of the frame. The sash cord will be tacked into a groove in the side of the sash; prise out the tacks to release it.
The procedure is repeated to remove the outer sash. Wedge it up, remove the weights and prise off the parting bead. Then you can lift the sash out and remove the cords.
Rehang the outer sash first. Holding the sash cord in a hank, tie a length of string to one end and attach a bent nail or a small lead weight to the other end of the string. Pass this over the outer pulley and let it drop inside the weight compartment. You can then retrieve it and use it to pull the sash cord through, ready to be tied to the weight. Now haul up the weight until it hangs just below its pulley, and pin the cord temporarily in place alongside the parting bead groove. Let it hang down towards the pocket, and cut the cord about 50mm (2in) above the top of the pocket piece. Repeat the process at the other side. Hold the outer sash in the frame, resting on the sill, and attach the cords to the sides of the sash with tacks. You should then be able to push the sash up to its closed position, checking that the weights drop almost to the bottom of the weight compartment as you do so.
Now replace the parting bead, and repeat the recording procedure for the inner sash; here, of course, the weights will be in the up position when the sash is closed, and drop as it is opened. Finally, replace the pocket pieces and the staff beads, and make good any damage to the beads with filler.
When carrying out this job, it is a good opportunity to repaint the sashes, since their sides cannot normally be reached for redecoration. If several coats of paint have already been applied, check that the sash is not sticking before adding another coat; it may be necessary to strip the old paint first if there is a severe build-up of paint.
Replacing a cracked or broken pane of glass is a relatively straightforward job, requiring more care and patience than skill. The most important point is to measure the rebate accurately before ordering the glass, and to
make sure that you have enough putty for the job — linseed oil putty for wooden-framed windows, metal casement putty for metal ones. You will also need small nails called glazing sprigs to hold the glass in place in a wooden window, and special clips for metal windows.
Wear stout gloves to remove the pieces of broken glass from the frame, hack out the old putty with a chisel or a glazier’s hacking knife, pull out glazing sprigs or clips with pliers and clean the rebate. Prime any bare wood or metal.
Measure the rebate both vertically and horizontally; if the frame is not a perfect rectangle, take the measurements of the shorter sides in each case, and subtract 3mm (1/2in) from each measurement to give you the ordering size. If you are using patterned glass, be sure to tell your glass merchant which way the pattern should run.
Apply bedding putty evenly round the rebate, locate the pane of glass along the bottom of the rebate and press it into position with gentle but firm hand pressure applied to the edge, NOT the centre, of the pane. Fix the glazing sprigs or clips to the rebate to hold the pane in place, and trim away the excess putty on the inside of the pane.
Next, apply the facing putty all round the rebate, and use your putty knife to finish it off at an angle of about 45° to the glass. Mitre the corners neatly, cut away any surplus putty and seal the putty to glass and frame by brushing over it gently with an old paintbrush or using a moistened finger. Leave the putty to harden for about 14 days, and then undercoat and topcoat it to protect it from the weather, taking the paint line on to the face of the glass by about 2mm to form a watertight seal.
If you decide to cut the glass yourself, lay the sheet on a flat table covered with an old blanket. Mark the cutting line 3mm outside the measured dimension of the rebate to allow for the thickness of the cutter. Lay a straight-edge between the marks and make a single firm but smooth stroke of the cutter across the glass against the straight-edge. Lay the score line over one edge of the straight-edge and press evenly for a clean break.