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I am building a porch swing out of leftover lumber. It is intended to hang in a covered porchh. Some of the lumber is not pressure treated. Is that okay for outdoor under porch as long as I stain and seal with spar varnish

  • Pressure-treated wood is treated with preservative so that if necessary it can have nothing else done to it and it won't rot easily. So yes it's perfectly OK to make something like a porch swing from non-treated wood. This is the case even if you don't then varnish it. – Graphus Oct 22 '17 at 22:48
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    @Graphus Answers don't belong in comments :) – mmathis Oct 23 '17 at 14:15
  • @mmathis And yet do you know how many there are in Comments here? Easily over 100. – Graphus Oct 23 '17 at 20:52
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For lumber to rot you need (long term) moisture. So under your porch you normally don't even need to varnish it.

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I would be more concerned about using PT wood that comes in contact with skin or even clothes. Pressure treated means pressure treated with chemicals. CCA or chromated copper arsenate has been replaced by copper-based pesticides, but chemical it still is.

If you don't need it for it's water/bug decay properties, don't use PT wood. Under your porch, you can use framing lumber.

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    I don't like the idea of this myself (prefer to err on the side of caution) but concerns over direct skin contact with pressure-treated wood do seem largely unfounded. It's probably the case, as with so many things, that the exposure would have to be frequent and over long periods for there to be any issue. – Graphus Oct 23 '17 at 20:55
  • @Jim I have been told that newer PT lumber is much, much safer to use these days. Because I just built a bunch of garden beds over at the community garden and we used PT wood. At the time people were concerned that the vegetables would get the chemicals from the wood, making it unsafe to eat them. But, I do remember that 'back then' the wood that was PT was unsafe. But now these days, I thought it was very safe? Unless what they use is not safe. Also last thought, is covering a porch in varnish going to last? I don't think that would last in weather, in the long run. – Ljk2000 Oct 25 '17 at 13:50
  • "chemical it still is"? So are cellulose and lignin (very complicated chemicals). Most hardwood is at least mildly toxic too (if ingested when finely divided). I'd avoid PT wood where babies might chew on it, but otherwise it'll be fine. – Martin Bonner Aug 15 at 12:34
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I would go with untreated wood and then just apply a good quality wood stain, tinted to whatever shade you like. Hint: It is much easier to apply the stain on all sides and surfaces BEFORE building the deck!

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