Wash the teak piece with mild detergent and water. This will remove any dirt and mold build-up on the surface. If you have severely weathered teak with cracks in the wood, you may need to wash several times in order to remove all the dirt. Allow the wood to dry overnight.
Sand the wood with fine grain sandpaper (320-grit is recommended). Continue sanding until you notice the original golden-hue return. Make sure to sand lightly to avoid scratching and follow the direction of the grain while sanding. Wipe away any residue from the wood with a dry cloth.
Apply a layer of high quality teak oil using a soft bristle brush. Wipe off the excess using a dry rag cloth. Allow one hour to pass between coats so the oil can be fully absorbed by the wood. You will notice the teak begin to turn a rich amber color, with a honey glow. On a more aged piece you may need to apply as many as five coats to restore its original luster. Once all coats have been applied, allow the chair to dry completely, followed by a final buff to complete the restoration.
Preserve the look of your teak by using waterproof outdoor furniture covers when not in use. This will help shield it from the sun's damaging rays, and protect it from other outdoor elements.