When speaking to deck care professionals about watersealants, it is difficult to decide which one is best for your deck.  The information will range from products that last 5 years to products that will only hold up for 6 months.  Every deck is different so there is no way to precisely conclude how long a product will last.  There are some facts to keep in mind:

1)  If a deck gets gray after it has been professionally cleaned and sealed, it does not mean that the sealant did not hold up or is defective.  The graying is caused primarily by the sun and clear products are not designed to prevent this.

2)  Even though clear watersealants do not prevent the deck from getting gray, they are just as effective in preventing water damage and mildew growth as their pigmented counterparts.

3)  Watersealants that contain pigments are designed to slow the graying process.  Even though many products say they are "clear", that phrase in their title refers to "transparent".  Be sure to test a small area of the deck with any sealant that has pigment to verify that you like the color.

In deciding which product to put on your deck, you should decide what your primary objective is... to keep the deck looking new longer or simply to protect from water damage.  If you can not stand the old look a gray deck gives you, then by all means you should have a pigmented sealant or UV sealant applied.  The most common pigment used in many sealants you will find in home centers is a "cedar tone".   Cedar tone is a natural wood tone that enhances the natural color of the deck.  

If you decide to go with a UV sealant, you can expect it to last (not allow the deck to get gray) for approximately 2 years.  This time varies from deck to deck due primarily to tree cover around the deck.  The important point to note here is there is no sealant on the market that will last for more than two years with regard to color retention.  Clear sealants on the other hand allow the deck to start graying in as few as 3 months.  This does not mean that your deck will look like it did prior to being cleaned.  That old, nasty look will take a few years!

Deckshield strongly recommends that you select a UV Sealant as the deck will have a "finished" look that will last much longer!