Should you apply sealer to a wooden deck? The answer is that it depends on the type of wood. Redwood and cedar do not need it because they are so naturally rot-resistant. So applying sealer to them would be waste your money and time.
Outside of redwood or cedar though, other wood types can benefit from being sealed. Sealing decks will extend their lives and improve their looks. Sealers with UV protection specifically can help keep the wood looking natural, rather than turning dark or gray, depending on the amount of sunlight on the deck. Having the sealer also prevents it from wetting and drying during the different seasons, which keeps precipitation from going in and expanding or contracting the wood as well. In the long term, this means the wood will not degrade as much.
There are three different types of sealant you can use on a wood deck: clear, semi-transparent and solid color staining. Some clear finishes let the wood gray naturally while others can preserve its natural look. Semi-transparent offers protection against UV rays and adds color. Solid color provides the best protection against UV rays, but it does remove the natural beauty of the wood by changing the color. Be sure to clean the deck before applying the sealer, as dirt and grime can be sealed with the wood if you don’t prepare it ahead of time for whichever type of sealer you chose.
It’s always best to use a penetrating sealer to reduce the tendency to crack and splinter. Look for penetrating specifically on the can of sealer. These sealers do much better than cheaper sealers that just lay a thin film on the wood. It’s always best to do the sealing soon after the deck is constructed and then reapply the sealant every year to five years, depending on the climate you live in.