If you find that one of your windows is sticking, the problem is almost certainly due to one of three things — a build up of paint, the frame swelling because of damp, or loose joints. Here is exactly how to fix a stuck window.
To get rid of a buildup of paint, simply strip the window back to bare wood in the problem area — by sanding, scraping, or using paint stripper. Once there is adequate clearance —about 1.5mm — between the window and the frame, prime and repaint.
First strip the paint back to the wood. The damp will have prob ably loosened the paint in any case, but if not, you can use a blow-lamp or paint stripper and steel wool. If you use a blowlamp, be careful not to damage the glass or burn the wooden frame or putty.
Dry the wood thoroughly — it is best if the wood can be allowed to dry naturally, but if this is not possible, a hair dryer or fan heater will do the job.
Rub down the area that is sticking with glasspaper or trim it with a plane.
Once the window opens and shuts smoothly, you can repaint.
If your window joints have worked loose, strengthen the joints with steel brackets.
Close the window and drive wedges between the window and the frame to force it straight and close up any gaps in the joints.
Hold the brackets in place to mark the positions of the holes, then drill the frame and screw them in position.
For a neater repair, you can conceal the brackets. Mark the outline on the frame and cut a recess with a chisel and mallet.
Then screw the corner piece firmly in place.
Cover this with finesurface or wood filler to give a smooth finish. Prime and paint the repair to match the rest of the window once the filler has dried.
Any gaps in the joints of the frame will close once you have wedged the window. Always put the bracket on the outside so it is not visible inside the room
For an even neater and more professional finish, if the mortise and tenon joints in your window are loose, but otherwise in good condition, you can take them apart, clean and reglue them. Then fit wooden dowels across each joint to strengthen it.
Make sure that you drill straight through the centre of the tenons.
Insert adhesivecoated dowels and allow to dry, then trim the ends and smooth flat.