Hi Bruce: I redecked my trailer using 2x6 treated lumber & covered it with a Benjamin Moore Paint product called Wolman F&P Finish & Preservative. This is a stain. It worked great. The B Moore salesman told me to apply a second coat while the first coat was still wet. Sounds unusual but it works. As soon as the deck was finished I stained it. Both applications were liberally applied. Good Luck.
PT wood leaches the preservative for quite a while so it might be a good idea to let it sit for a few months [some say as much as a year] before staining. Then, depending on the amount and intensity of exposure to the elements, you may want to put a quick recoat on it about every 2 years --- on the decking and other parts directly exposed to the sun, not everything.
Best amount of time is 1 Season.
That is about 2-4 months, dependant on the weather. If you are having a very damp rainy season (Like alot of people are having right now)..give it at least 4 months. As you know, PT shrinks as it ages and dries. The average amount of decking shrinkage is approximately 3/8" between boards. You can use that as a rough estimate to approximate drying time.
The correct answer will depend upon the climate, the current moisture content of the treated lumber and the type of sealant or stain one plans to use.
In arid dry climates, sealing immediately could yield the best results. By sealing in moisture one will prevent cracking, splitting and warping of the wood by allow the moisture to acclimatize to its surroundings more slowly.
Even in wet climates, sealing can be done immediately is one uses kiln-dried-after-treatment which comes ready to use at a 15% or less moisture content just like framing lumber.
Type of sealant can determine when to apply. Some formulas are made to applied when the lumber is fully wet. Others need lumber to naturally air dry to a moisture content of about 15-19% before applying. Such moisture content in lumber can be difficult to achieve in wet warm climates.
I'm a fan of Flood's "Clear Wood Finish". Some of Flood'd products like their Dock sealants are intended to be applied when the wood is fully wet.
Wolman's "Wood Preservative" mentioned above is also a good treatment.
In my region (Mid-Atlantic) I routinely seal treated lumber immediately upon or prior to installation for best results.
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