It's exposure to the UV light from the Sun that causes wood to turn grey
It's absorbtion of rain water and snow melt that causes wood lumber to
split at the ends of each board.
If it wuz me, I would simply use a deck sealer on your wood, and apply
it with a paint roller sleeve using a paint roller frame and a 5 foot
My experience reading and answering posts in these DIY forums is that
most people prefer Cabot or Olympic deck stains. I've not heard much
praise of Thompson's Water Seal. I think deck sealers would not only
prevent absorbtion of water into the wood, they'd also probably have
some UV blockers in them to protect the wood from UV light as well.
And, considering that lumber absorbs liquids through the end grain 15
times as fast as across the grain, I'd also use a brush to paint the
exposed end grain of any boards in your deck as well.