Outdoor elements can reign havoc on the wooden parts of outdoor structures such as a canopy gazebo, a canvas gazebo, or a wooden park bench. Moisture can attack outdoor wood in a way that has nothing to do with rot. Wood swells when it is wet, and shrinks when it is dry. It is important to have a good gazebo cover on your gazebo. Most often a canopy gazebo will be placed on top of a wooden foundation. This foundation needs to be weather proofed against the rain and other elements.
This natural cycle is heightened even more by freeze-thaw cycles. When structures, such as a canopy gazebo, have to withstand these conditions, it can really take a toll on boards, especially at all the points where boards are fastened. Following a good rain, the underside of a decking board will retain moisture, while the sun-drenched surface will quickly dry. The difference in moisture will create stresses that can eventually lead to cupping, cracking, and splitting.
Pressure treatment and other chemical preservatives are not designed to provide defense against this kind of moisture damage. Moisture will move in and out of a treated board just as readily as if the board had not been treated. Either way, the board will have the same tendency to crack, split, and warp whether it is on the canopy gazebo or other garden structure.
In general, the heavier woods, southern pine, the most pressure treated wood, will suffer more from moisture movement than will lighter woods. Heavier woods, such as redwood and cedar, a common wood used for decking under canopy gazebos , are more sponge-like, meaning that water can more easily pass through them with less effect.
*If you are looking to waterproof your gazebo canvas or canopy top, there are some great products on the market for that too.
The only way to reduce water is to use a water repellent. An excellent water repellent is a good coat of paint. I have found this alternative to work for me. My flooring has been painted and has helped my canopy gazebo withstand the elements. The alternative to painting will be purchasing a clear repellent often marketed as a sealer. The most common clear repellents on the market are no more than paraffin wax dissolved in mineral spirits.
When you apply the repellent, the solvent evaporates, leaving the wax in the pores of the wood. The wax impedes the flow of water vapor in and out of the wood, and this decreases the rate of expansion and contraction. As a result, the wood is less likely to cup. You can buy water repellents that also contain fungicide. Some clear penetrating finishes are formulated with linseed oil, tung oil, or alkyds, like many paints or varnishes, but instead of acting as a film-forming agent, the resin will act as a sealer.