My husband is installing a new deck with pressure-treated lumber at our home in Tennessee.
How long does he need to wait to paint, or should he stain the deck now?
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I am a painter and I build also and I personally will not warranty the work unless it's after 6 months. Pressure treated (PT) lumber takes months to shrink and re-contract on and off so the paint will crack and not adhere correctly. Also, the PT you buy at Lowe's or Home Depot gets moved around a lot so you may have a load of wood with boards that are weeks apart from drying. Personally, and unfortunately, I would wait longer than a month. I live in Vermont and we're known for tearing our decks to hell due to the non-stop rain and snow, but that's what I've heard a lot: 6 months.
I think I answered a question similar to this before but I actually contacted Universal Forest Products last fall about using pressure treated lumber in a basement. Tons of great stuff they sent me.
Some good points:
In a dry basement wait 2-3 weeks before installing drywall over (they want you to use PT for everything in the basement and they make good points)
outside you should wait 2-3 weeks before painting or staining in moderate temps with no to little rain. This is a little tricky because you want to install PT lumber right away since it will warp quick. You can't let it dry out before installing unless you can apply a serious amount of pressure on all sides of the wood.
For your question it depends on the climate/weather. If you have two weeks of dry 100F weather you will be fine. If it rains on the lumber a few times it gets tricky. Water isn't just soaking in the wood but it dramatically hinders the drying out process.
When you're shopping for PT lumber, look for the lighter, dryer pieces when sifting thru stock, but be sure to pick the pieces that are uniform and straight. This will help you get a jump start on the drying process. I do a lot of stain work and I would wait three to four weeks if possible to stain after purchase. Keep in a dry, weather proof area if possible - a garage, shed or workshop. If you have to keep the lumber outside, elevate it on some 4 x 4 runners and expose it on clear days. Keep tarped during wet days.
Here in Norway the local 'wisdom' is to install the pressure treated timber one season and stain it the next.
As a builder I agree with some of the above comments that the timber can take a considerable time to dry out. However, a few weeks of good weather should get it dry enough to take a finish, but I'd use a moisture metre and check the (finish) products specs to be sure. I've just waited 6 weeks for some balustrade tops and I'll chance a coat tomorrow weather permitting.
A one month minimum dry time is recommended. That said, I'd wait as long as the painting season permits. If you have three months before it will get cold down there, then wait until then. It's important to have three good, consecutive dry days before applying the stain when ultimately decide to do it. And two-coat everything with a quality stain. Ask the paint store person about doing it and which product to use. Some stains are meant for walls and some for walking on.