Always wear thick gloves and goggles when reglazing. Break out a broken window pane, using a hammer and pliers, and carefully catch and dispose of the glass, wrapping it in several layers of newspaper. Levering out pieces around the edge will also break out putty, but remaining putty should be removed with a woodworking and spread to the edges of the rebate.
Press in the glass, by working with the fingers around the edges. Do not press at the centre of the glass. Remember that the point where it is bedded down on the putty will be visible, so try to get an even thickness behind it. Tap in sprigs in the case of a wooden frame or fit wire clips if the frame is metal. The sprigs do not have to go in very far and may be tapped in by sliding the edge of a chisel or a light hammer across some card over the glass.
More putty can be added from the outside with the fingers, but it will have to be pressed in and smoothed with a putty knife. One with a diagonal cut across its end is suitable. Press the putty down so it bonds with that already in the rebate and draw the knife along so the surface is bevelled to come just below the rebate seen through the other side. Use the straight edge of the knife to make neat mitres at the corners. Surplus putty can be cut away with the knife from both sides of the glass.
Wipe around the putty lightly with a damp brush and leave the putty to harden for about a week. Clean the glass and paint the putty and the frame. Carrying the paint line a very short distance on to the glass may prevent water getting behind the putty and loosening it.
Wood expands and contracts according to its moisture content and this depends on the weather for outside woodwork. Wooden window frames set in brick may develop gaps where water has entered and this causes rot. Do not fill these cracks
with concrete, mortar or putty, as these set hard and do not allow for movement.
Buy a mastic sealer from a builders’ merchant. This may come in a tube, so that you squeeze the sealer through its nozzle, or it may be in a gun with a lever action. Squeeze this into the gaps. If necessary, press in further with a putty knife, which should be kept wet to prevent sticking. The mastic will set sufficiently hard to take paint, but it remains elastic so that gaps will not form.