Wash the teak furniture to remove all traces of dirt and body oils. Mix trisodium phosphate (TSP) with plain water in a clean plastic bucket, as directed on the TSP container.
Sponge the TSP solution over the teak wood, rubbing lightly with a sponge before rinsing the furniture off with a water hose. Let the furniture dry completely.
Sand off the top layer of gray teak wood with a fine, 320-grit, foam sanding pad.
Use short, back-and-forth sanding motions in the same direction as the wood grain. As you sand you will begin to see the natural teak color appear.
Continue sanding until the entire piece of furniture looks fresh and new and no gray weathering remains.