The best way to cover all horizontal walking areas (flooring and steps) of your back deck is to use an oil based semi-transparent stain or a clear sealer.
The problem with painting these horizontal areas of your deck is that the paint just “lays there” on top and will not be absorbed into the wood. As a result, those areas will hold water on top of the paint and prohibit any underlying wood moisture from evaporating into the air above the deck.

It’s a double edged sword that traps moisture into the wood. Over time, as your deck boards expand and contract with variations in weather conditions and temperature, the paint will begin to chip and peel, and the underlying back deck wood begin to soften and rot.

A quality stain, however, penetrates the wood grain to seal it, while also allowing moisture to escape from the wood. It won’t chip, peel or crack as the deck wood naturally swells and shrinks during changing weather conditions.  Advantages of using a semi-transparent stain on your deck include:

• Longer lasting, and more durable.
• Gives a more unified color.
• Hides defective and weathered wood.
• Does not tend to chip or peel.

It is recommended that a professional be hired to properly prepare and clean the deck to remove any remaining stain, sealant, dirt and grime. A properly prepared deck will yield the longest-lasting results. It is also very important that deck boards be completely dry before stain is applied. A wood moisture level of 15% or less is preferred.  Applied properly, a semi-transparent stain will also result in the most natural looking back deck.

While it is most important to stain deck flooring and walkable areas, it is acceptable to paint other non-walkable areas such as deck support posts, spindle, and handrails.  If you elect to go this route, it’s recommended to match the paint color as close as possible to the stain color.

Also, don’t paint unless you can cover all six sides of every piece of wood. In situations where pieces of wood are sandwiched together, and the joined surfaces can’t be painted, then the pieces should be joined as one by thoroughly caulking all connecting joints. If all sides can’t be reached, you’ll get the best protection with an oil or oil-stain finish — not with paint.

Never paint a wood surface that has previously been oiled. The paint won’t stick, and you’ll have a mess on your hands forever. After wood is oiled or oil stained, even the most minute spots of leftover paint show up like a headlight on Lover’s Lane. If you insist on painting an oiled surface (or on oiling a painted surface), you must first take the time to use a paint remover followed by thoroughly sanding the wood.