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I have just built my very first picnic table (really, my very first anything). I used pressure treated lumber and galvanized hardware.

I would like to seal the table before I put it outside, but I'm told that you need to wait ~ 6 months before sealing pressure treated lumber. This stuff says that you don't need to wait, even on pressure treated lumber (though I can't find it anywhere).

Question: What's best thing to do here? Can I seal it now so it doesn't get discolored?

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Note that you can't use plain galvanized hardware on PT lumber. You need to go with hot-dipped hardware (or hardware explicitly labeled for ACQ use). As for 'that stuff' if it says you don't have to wait, I guess you don't. The reason to wait is typically that PT lumber is sopping wet and needs plenty of time to fully dry out. –  DA01 Apr 9 '13 at 18:43
    
A pressure treated picnic table? I'll have my hot dog with a side of arsenic. –  Tester101 Apr 9 '13 at 19:11
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@Tester101 while I probably wouldn't use PT myself for a table, most PT (at least in the US) is now ACQ rather than Arsenic based. –  DA01 Apr 9 '13 at 19:17
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I'd still at least make the eating surface out of Cedar. –  Chris Cudmore Apr 9 '13 at 19:17
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In my opinion, products like Thompson's or any of the clear water seals are a complete waste of time and money. Opt for a good grade house siding stain with a fungicide. They come in transparent to solid color. Wait a month or two or until you can see and feel the PT to be fairly dry and the grain starts to slightly open a bit. It is not going to open like a crack, but you will see the grain more distinctly when dry. –  shirlock homes Apr 9 '13 at 20:47
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2 Answers

up vote 1 down vote accepted

I used PT lumber for my basement outer walls. I emailed PT lumber association (yes they have a website) and and asked how long I should wait before I slapped up the drywall. I was told that unless the lumber is in a very humid environment it will lose most of its moisture in 2-3 weeks. I waited a month to be safe. If the lumber is outside in warm weather shorter than 2-3 weeks. They actually said I would be within code within a few days but the 2-3 weeks was just a safety precaution. I just didn't want moisture hitting the drywall.

There is no arsenic in PT lumber now. But if it is a picnic table a "sealer" that is good then it will be full of chemicals. I would almost go with an oil based paint.

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There's probably no code for what you can make a picnic table out of, but PT lumber doesn't sound like a good choice to me. PT is probably still not allowed in houses in most places. It's got to have something bad in it, even if they changed it. I would use regular lumber and finish it with some sort of finishing oil.

As to the comment about making the top out of cedar, I think there are just too many splinters in most types of cedar, and that would get worse as it weathers.

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Where isn't PT lumber allowed in houses? Years ago they quit putting arsenic in PT lumber. It is no longer in there. In almost all counties PT is required for wet situations (basement floors). –  DMoore Apr 12 '13 at 4:28
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