Whatever you do…Please Do Not use a Pressure washer on your redwood. I have seen hundreds of decks , siding and other wood ruined by these high pressure termites. Not only do they inject water into places it was never meant to be ,it literally tears wood fibers to bits and basically turns wood to mush.
I would first Scrub the deck with a bleach water solution and allow to dry. Then I would get in touch with a high quality paint company and have a salesmen design a "System" for the rejuvenation and coating of my deck that will be tailored to my location.
Do not confuse Home Depot or Lowes with a High Quality paint company.I am talking about Glidden or Sherwin Williams etc. People who have been selling Paint and Coatings for 100 years plus and salesmen who have been selling coatings and Solving coating challenges for years. Not like the Box Stores where the employees were selling shoes last month and now Pushing paint. Good luck

The first part of the process is to clean the old stain off the decks. You will also want to spot treat anything like oil or paint spots. You can spot clean them with deck stain remover or deck cleaner in its concentrated form.

Once the spot treatment is done you will want to get the deck wet with a garden hose to let the surface become porous and more receptive to the cleaner. You can use just about any deck cleaner mixed with dish soap or mild detergent. Pour a good amount of cleaner onto the deck and sweep it vigorously with a stiff brush to clean away the top layer of deteriorated wood.

Be sure to wash away the cleaner frequently. It’s better to apply the deck cleaner in small areas so you can scrub it, clean it, and then wash away the cleaner. Once the deck has been cleaned, try to keep the dirt and dust off it until you stain it. You should let the deck dry completely before applying the stain. This will usually take about three days.

There are a lot of people that hear about deck stains and deck sealants and they get confused between the two. Most of the quality deck stains available are both stain and sealant in one, so you don’t need to worry about which one to use. I prefer a deck stain from Sherwin Williams called “DeckScapes”. It is about the best quality I have seen, but it costs a little more than some of the others. I also like Cabot, but I won’t use Behr.

You will want to apply the deck stain in the morning when the sun isn’t hot. The deck needs to be cool and the temperature needs to stay above fifty degrees until the stain completely dries to make a good seal. Apply a generous amount of stain because it is two-fold in purpose. It is making the deck look nice and it is protecting it from the weather. I mention this because I have received letters from homeowners that apply only enough stain to their decks to look nice, but they have to apply it every year.

You most likely won’t be able to stain the underside of the deck, but it doesn’t matter. If you can’t see it, the sun probably can’t get to it either. When the deck is wet from the stain, it will be very susceptible to dust and footprints so try to keep the kids off of it for at least two days if this is possible.

I used to use power washers on my Redwood decks, but I was young and dumb back then. Now, I just use the cleaner and a stiff deck brush or broom. Some power washers can damage and splinter softwoods like Redwood, Cedar, Pine, and Fir. If you’re in a super hurry then go ahead and use a power washer, but if you love your decks like I do, then be gentle and give them the TLC they need.

If you want to experiment with different shades of stain, then you’ll have many options to choose from. The most important part of the stain is to slow down the deterioration process of the wood, so regardless of color, be sure that is a good sealant stain.

That’s all there is to maintaining your Redwood decks. Remember, an ounce of prevention is worth a ton of new decking materials. I hope you enjoy your decks as much as I do.

I agree with the others about not using a pressure washer, but if you must, make sure you know what you’re doing. Using the right degree tip and lowering the pressure can make it easier on you without ripping up the fibers and impregnating the wood with water. But if your a novice to pressure washers, you WILL destroy the wood. You will need to sand the surface either way, preferably "with the grain" with a belt sander. It will really pretty up the wood again.

Redwood is a plentiful and renewable resource, but some environmentalist extremists convinced the federal government that harvesting was hurting the Spotted Owls habitat. If you can find some, it will cost you as much as a liver transplant.