Answers

Decks are a very tricky item to finish properly.  There are so many variables that have to be considered prior to applying any kind of stain.  If I were staining your deck, I would start by asking a series of questions:

1.) Where are you located? What type of climate is the deck going to be subjected to?

2.) What type of wood is the deck made of?  This will limit what kind of products you can use or would be best suited for the type of material used.  Some woods will only allow you to use an oil based product, while others you can stain with newer waterborne products.

3.) How is the deck built? Is it close to the ground (1'-2' or high up 5'-12').

If the deck is close to the ground, using a one coat system with an oil based product is best.  Although the solid color stains hold up well on decks closer to the ground as well.  

The biggest enemy to any deck surface is moisture, so having good ventillation is a key factor.

4.) What type of finish would you like to apply? Do you want a solid color stain (looks like a paint) or do you want a translucent/transparent or semi-transparent stain (allows you to see the natural grain of the wood)?

We recommend an oil based finish for translucent and semi-transparent stains and we recommend a waterborne product for solid color stains.

5.) When was the deck built?

The wood doesn't necessarily have to weather prior to staining, it just has to be DRY (typically less than 15% moisture content).  Once a tree is cut down, the wood starts to decay as it is no longer connected to a living water source.  The sooner you can protect the wood from the elements of sun and water, the better off your deck will be.  When you let a deck "weather" you allow it to suck up moisture and then have it dried out by the sun (repeatedly).  The more this happens, the faster the wood of your deck will decay.  This is why unprotected wood turns gray; the gray is the dead wood fibers.  If you left your deck to weather, you will want to clean it and remove all the dead wood fiber.  If you use a powerwasher, don't get too close!  The power washer is only meant as a way to help rinse off the deck surfaces.  The tip of the powerwasher should not get any closer than 10-12" from any wood surface, otherwise you can damage the wood.  Use a deck scrub brush and a solution to help remove the dead wood fiber.  Benjamin Moore has some great how to videos on their website: www.benjaminmoore.com.

As soon as the deck is dry (if new), it has to be sanded with about 80 grit sand paper to remove mill glaze.  This "glaze" is what happens when the wood is cut in the saw mill.  The mill glaze will prevent a stain from penetrating the wood properly and cause premature failure of the finished surface.

If you had to powerwash and remove dead wood fiber from the surface, you will want to sand the wood surfaces to remove any "furring" which happens during the process of removing the dead wood fiber and cleaning the deck surfaces.  Once again, use about 80-100 grit sand paper. 

6.) Let's set expectations...

Deck surfaces are subjected to all kinds of elements, foot traffic and furniture.  A typical finish will last for about 24-36 months before showing signs of wear.  Some higher traffic areas may see signs of wear sooner than that.  Be aware that if you live in a climate that gets snow, be careful if you shovel off the deck and try not to throw salt on the deck surface.  This will definitely shorten the life of the stained surface.  

Gently clean your deck once or twice a season to keep debris and dirt from the deck surface.  Doing so can extend the life of the product applied.

7.)  There are more variables and conditions to think about, but this should cover some of the major areas.  The best advice, if it is possible, go to a paint store (Benjamin Moore retailer or Sherwin Williams, or similar) and provide them information about some of the questions above.  They will be able to ask a few more questions and recommend the best product for your situation.  If you don't want to do the project yourself, they can usually recommend a trusted professional.  Try to stay out of a big box store as they typically don't have the best knowledge or training.  

Pictured is a deck during the cleaning process, removing dead wood fiber. The lower portion of the photo has been cleaned and the upper section still has the dead wood fiber.

The second picture is during the staining process.  The deck was sanded after cleaning and allowing to dry.  Stain one board at a time and keep a wet edge to avoid lap marks. Staining in pairs with a helper if possible is best.

Hope that helps and good luck with your project!

Mike