Any unprotected piece of wood left in the outdoors will show indicators of deterioration within a year or so. It’s in Nature’s character to bear down on materials that have turn out to be inanimate — and that includes pieces of lumber forming your deck or fence. In this case, sunlight and rain are her key tools. Wood exposed to sunlight out within the open turns weak and gray as the rays from the sun ruptures its internal fibers. A similar breakdown takes place when rain water soaks wood and makes it swell. The result is sponginess. Morning dew and afternoon sun then set a day-to-day wood swell-shrink cycle in motion, hastening the deterioration process. Grayed surface, deformation, splitting, and loosened nails are telltale indications of wood trouble for which the elements are responsible. I suggest you study research dealing with 1750 Psi Electric Pressure Washer.