I'm tempted to ask how come it has chunks of wood missing? You've not been biting it, have you? How big are the holes in it? You could fill them with wood filler if they're not too big, then sand it down when it's set and paint. If they're very big, they may need to have a piece of wood cut to size and set in with either nails, screws or wood glue. Fill the gaps round the edges of the fill with filler or mastic then sand and paint. If the holes are irregular in shape, they may need cutting square or to a more even shape with a chisel before you can cut wood to fit them. Difficult to say exactly without seeing the frame, but hope this has helped a little. Obviously, you may need to call in a carpenter if all this is beyond you. Best of luck, anyway.
Denis Langley, August 2005
