If you have a pressure treated deck and you thought that it would be low maintenance then think again. Although it will last about 15 years and that is much longer than untreated wood, you can expect to be staining and treating it every other or every 3 years as long as you have it. Now if you have a roofed off porch or a gazebo the area that is protected will last much longer between treatments and the vertical surfaces meaning the rails and posts will last a couple years longer between treatments.
When you first build with pressure treated lumber you will probably be amazed at the amount of moisture in the wood. When I picked my lumber out at the store the decking actually bowed a good foot or more when I was lifting it off the stack.
This is because this type of lumber goes through the normal drying process before it is placed in a sealed tank and treated with wood preservative that is sucked into the fibers of the wood. After it is treated it is shipped off to the stores for sale to you and hopefully its not so wet that it is leaking off of the truck as it goes down the highway. No actually its not that bad but it is extremely moist and has a higher water content than it was still a tree.
This is the reason that treating your freshly built deck or other outdoor item that is made of this type of wood.
Any product whether it is a spray on sealant or a stain or paint will not adhere properly to the surface and it will not penetrate into the pores of the wood to give it good holding and lasting strength.
Most manufacturers suggest that you wait a minimum of at least 6 months to stain or treat pressure treated wood and this is really your best bet. I would suggest that you let the surface go through a winter before you treat it.
Once the surface has leached out any excess product and stabilized you should then pressure treat the surface and allow the wood to dry for a few days. You really need a few good hot days in the 80’s before you treat the wood and no chances of condensation or dew overnight. You should also pick a time where you have a few days of good weather after the stain or sealer is applied so that it cures and won’t be damaged by rain. Rain will make the surface splotchy at best and may make the whole job look really bad. However it won’t normally cause the waterproofing to fail.
Although it is possible to pressure wash and then let your pressure treated wood dry for about a week and then treat it with a sealer or stain it is really not the optimal situation. Contractors might do this because of time constraints and normally because stain and sealer are designed to be used on this type of wood in an outdoor exposed condition the treatment won’t immediately fail.
On the other hand if you were to have a series of problems such as treating the deck as soon as its built and doing it in the late fall when temperatures are under 60F or drop below 40F over night and then you are hit with rain within 24 hours…. all of this will have an effect on the quality of treatment you will get. It just means a product that was rated to last a few years may need a freshening the next summer.
However waiting if an option is probably a good idea. The only thing I would suggest is if when you are building your deck if the joists and beams are not easily accessible that you treat them prior to putting on your decking. Its an added protection that will extend the life of the framing. In those situations I often wonder if asphalt sealer might do a good job on under deck structures but thats probably really not a great idea..
Good luck and get use to it because you can expect to be doing this every couple years from now on.