Ultraviolet sunlight discolors any type of wood you leave exposed to the weather, but that's not the only reason your fence turns gray. Salts in the air settle on the surface and add a whitish residue, and tannins from inside the wood leach to the surface and contribute dark gray streaks. Restoring the color is a two-step procedure that involves a thorough washing and a bleach treatment. Preventing the wood from turning gray again requires a protective finish that blocks UV sunlight. The best option is an oil-based semitransparent stain.
Clear away any foliage covering the fence and move lawn furniture a safe distance away. Clear the area of children and pets. Put on sturdy, close-toe shoes.
Connect a power washer to an outdoor water supply, and attach a tip with a spray pattern between 15 and 40 degrees Fahrenheit. Use a white 40-degree tip for superficial dirt, and a green 25-degree or yellow 15-degree tip for deeper cleaning. Avoid the red 0-degree tip -- it can gouge the wood.
Start the power washer and clean the wood by moving the tip along the grain. Keep the tip at least 6 inches from the wood to avoid splintering or gouging it.
Wash the fence with a solution of water and a commercial exterior wood bleach that contains oxalic acid. Wear gloves. The bleach removes dark tannin stains and iron oxide stains from nails without changing the natural color of the wood. Apply the bleach with a sponge or paintbrush and let it soak in, then wash it off with the power washer, using a white tip.
Let the wood dry for one or two days. Apply a semitransparent stain with a paintbrush. Make sure the stain contains a mildewcide to prevent blackening from mold, and use a stain that matches the natural wood color for best effect.
Tips & Warnings
- Keep the fence looking new by reapplying the stain every 3 to 5 years, depending on the amount of rain and sun it gets.
- If you don't want to hide the natural wood with a pigmented product, seal it with a clear, waterproofing sealer. It won't stop the fence from turning gray, but it will protect the wood from water and make it last longer.
- Power washers are dangerous because the high pressure can force water through skin. Keep your hands away from the spray, and never point one at anyone else. Wear protective shoes, just in case, but take care to not point the hose too close to your feet.
- Wear protective goggles before spraying the bleach off the surface so that your eyes are protected from the mist.
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