Protect wood surfaces from overexposure to the elements. Keep wood painted if it's painted; stained and varnished if it's stained and varnished; water-sealed if it's water-sealed.
Exposing untreated wood to direct sunlight will dry it out and can not only bleach it out, but also set it up to be infested with dry rot. If the wood you want to restore is already dry, suspect dry rot and treat accordingly.
Check for crumbling soft spots. These must be removed and the wood either replaced or filled.
But first, you must treat to restore some moisture to the wood and kill the rot before painting or finishing. Once protected, you should occasionally use a humidifier near your inside furniture if the air in your house is hot and dry.
Doing so prevents drying and warping. Also, avoid placing wood furniture near forced-air heater vents.
Clean Wood Surface
If wood is very dry and has peeling paint, shellac, wax or other coating, clean the wood with a soft cloth dampened with soap and water. Use the appropriate chemical to remove old finishes.
Apply a mixture of 1 part turpentine to 3 parts boiled linseed oil to older finishes. Gently scrape off old paint or varnish and wash the surface again.
Dip a cloth in the turpentine and linseed oil mixture and rub into the wood a small area at a time. Clean narrow spaces or grooves with a toothbrush you've dipped in the mixture.
Treat and Protect
If you find rotted wood, dig it out and fill the cavity with an epoxy wood filler. However, before you fill the wood, treat for wood-rot spores.
Borate mixtures prevent wood rot in new wood and kill rot causing organisms in infested wood. Ethylene glycol mixtures are toxic to all sorts of wood-destroying fungui and insects.
Both are water-soluble and penetrate dry wood, especially glycol compounds. Rub the solution into the wood, allow to sit until absorbed and then wipe the surface.
Finish with your choice of paint, varnish, oil or water sealant.
Homemade borate treatment is 60 percent borax and 40 percent boric acid. Boric acid is often sold as a roach poison.
Borax can be obtained online or from cleaning supply stores. The chemicals are mixed with water according to label directions and combined over low heat till the crystals completely disappear.
Use the mixture at temperatures above 40 degrees.
A glycol treatment for dry rot is 50 percent glycol antifreeze, 28 percent borax and 22 percent boric acid. Mix crystals with water according to label directions, mix in proportions indicated and heat slowly till boiling gently.
Use a candy thermometer. When the mixture reaches 260 degrees, most of the crystals are completely dissolved.
Cool before applying to bare wood. Use above 40 degrees.