In case you’ve got wooden-framed French doors which have seen better days but still work good, it would be a pity to replace them. This is a common issue for doors which are exposed to the elements. The end deteriorates, the wood expands, contracts and pores open in the timber. Moisture penetrates into the pores and causes rot. This usually happens around the outside of the door and doesn’t actually influence the integrity of the doorway. If yours has rot but still functions fine, don’t replace it. Repair it with leaf adhesive that penetrates and dissolves tough as glass.
Remove the doors in the hinges; use a drill/driver to remove the screws holding the hinges to the jambs. Place the doors across sawhorses. You don’t have to remove the seams or hardware.
Scrub the rotten area gently with a wire brush to remove loose particles and wood fibers. Brush out the rest of the particles using a paintbrush.
Mix the powdered leaf adhesive with water based on the manufacturer’s directions. Dip the paintbrush to the glue. Apply the glue to the rotten location. Use the close of the brush to work it right down into the rot if necessary. Completely saturate the rotten area using the glue. The glue will penetrate into open pores and harden. Allow it to soak in for five minutes, then scrape the glue off the doorway with a flat rod. Wait overnight for the glue to dry. Turn the doorway above, and perform the other side if necessary.
Sand the door extensively with an orbital sander using 100-grit sandpaper. Sand off all the previous finish on the side of the doorway which you’ve been working on. It should come off easily. Sand the door again by hand using 100-grit sandpaper. It is possible to do both sides if required, or leave 1 side as-is if there’s no rot on that side.
Apply a heavy coat of Danish-oil stain to the doorway on the side or sides which you sanded. Use a sponge to apply the stain. Allow it to dry for 15 minutes, and rub it away with a cloth. Wait overnight. Apply another coat of Danish-oil, and rub it away immediately. Rehang the doorway on the jambs.
Apply additional coats of Danish-oil stain each six months to safeguard the door. For a little more shine, apply paste wax to the doorway, or use your pick of polyurethane, varnish or shellac.