preservative for pressure treated lumber
Excerpts,
Quote:
Fences
Fences are fully exposed to the weather, and have at least some parts in contact with soil. Care must be exercised in selecting and applying a finish to obtain a reasonable service life.
Many fences are left to weather naturally. However, if a finish is desired, semi-transparent penetrating stains or water-repellent sealers/preservatives that contain a mildewcide (or otherwise are resistant to mildew) are preferred. These finishes are absorbed into the wood without forming a film; they do not crack or peel. Stains come in a variety of colors and show the wood grain.
Quote:
Decks & Porches
Decks and porches present a particularly severe exposure for both the wood and finishes. Most wood members are in a horizontal or flat position. These horizontal surfaces, especially in decks, are often exposed to the direct rays of the sun and tend to collect moisture, so the weathering process is greatly accelerated. As repeated cycles of wetting and drying occur, checks tend to enlarge rapidly into cracks and, along with the end-grain surfaces, begin to retain moisture. The conditions for decay and insect attack caused by the presence of moisture are thereby greatly improved.
Any film-forming finish is likewise subjected to excessive stress because of the continuous shrinking and swelling of the wood that results from changes in its moisture content. Furthermore, the finish is subjected to abrasive wear, particularly in high-traffic areas. By design, porches are somewhat protected, so the conditions are not normally as severe as those with decks; however, the same conditions — moisture, sun, and abrasive wear — are usually present at least periodically.
For fully exposed decks, a water-repellent sealer or a penetrating semi-transparent stain may provide the best finishing solution, even on wood that has been pressure treated with preservatives. Special formulations made specifically for decks are available. These penetrating deck finishes, at least the water-repellent sealers, may have a shorter service life than paint, but they are more easily renewed. For severe exposures, the finish should be renewed annually; spring is usually the best time. Light-colored penetrating stains will also last longer than dark ones on flat surfaces subjected to traffic, because light stains show the least contrast in grain color as wear occurs. The penetrating finishes need to be refinished every 1 to 2 years.
If it were me, I would let it weather for one season, then I would treat it with a transparent penetrating stain. Depending on local weather conditions, re-treat it as needed.