Teak cleaners are incredibly useful for removing grayness, old oils or sealers, and stains on teak. Two-step or two-component teak cleaners have a first step (cleaning), and a second step (neutralizing the first step, and brightening). The key to a good teak cleaning job is to follow the steps carefully and not deviate from the recommended procedures. In addition to teak wood, teak cleaners will also perform well on other oily hardwoods, such as mahogany.
First, mask off the area properly. Some painted surfaces and aluminum substrates can be damaged by the chemicals, so mask or remove hardware, as needed. Completely wet down the surface to be cleaned, as well as any area that the cleaner may touch. Doing so will help prevent the cleaner from drying out the wood, increasing stains, or creating an inconsistent appearance. Always wear proper protective clothing and use safety equipment, as directed.
Only attempt to clean a few square feet of surface at a time. The first component is used for the cleaning step, and is generally referred to as Part A, or Part 1. Apply by pouring the material or by using a garden sprayer. Do not use any sprayer that may aerate the material. Use a soft nylon bristle brush or abrasive pad (such as Scotch-Brite™), and scrub lightly across the grain. Scrubbing with the grain can raise the grain excessively or push contaminants back into the grain. You'll notice that the liquid will darken and contaminants will start to come out of the wood. After a couple minutes of scrubbing, rinse the entire area thoroughly with fresh water, removing all of the cleaner. Lightly scrubbing while rinsing may help remove the contaminants and the cleaner. Clean the brush or abrasive pad by rinsing thoroughly with clean water. Complete the cleaning process on the whole piece before moving on and using the second component.
Once the first component has been rinsed away completely, and while the surface is still wet, apply the second component (brightener, Part B, or Part 2) in a fashion similar to the first component. Scrub lightly across the grain with a brush or abrasive pad. As the chemical starts to work at neutralizing the first component, the wood will turn from a dark brown tone to a warm red tone. After scrubbing, rinse thoroughly with fresh water. Be sure to remove all of the second component. Rinse off the entire area. Use the second component to remove any stains on fiberglass or paint, then, after a few seconds, rinse it away with lots of fresh water.
Allow the teak to dry completely. If any stains are still present, it's recommended that you repeat the cleaning process. Most teak cleaners direct you to wait 24 hours before applying any sealers or oils to the wood. Before applying sealer or varnish, a light sanding (in the direction of the grain) with 220-320 grit sandpaper will go a long way to remove the raised grains while retaining as much of the wood as possible. For varnish applications, before sanding and applying the first coat of varnish, it may be prudent to wait 3-5 days, allowing any moisture in the grain to evaporate.