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I have a 2x6 deck board (treated lumber) that is 14 feet long and it's lying across 6 joists and a ledger on the east end and a frame board on the west end. Right now it's not screwed in anywhere. If I stand on the east end of the board the west end lifts up on the north side, and if I stand on the west end of the board the east end lifts up on the south side.

This board is expensive and so I want to straighten it out so it's flat all the way across the deck.

Any suggestions? The only power tools I have to work with are a Sawzall, a circular saw, a jigsaw, a Dremel and of course my impact driver. I've thought of putting a clamp on the west end to hold it down but I'm looking for the best professional solution.

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  • If you place on the 1.5” edge, are there any joist gaps? Sep 10 '20 at 4:45
  • Yes, there are two gaps on the 1.5 edge; one on joist 3 and one on joist 4. There are 6 joists and I’m numbering east to west. Sep 10 '20 at 23:29
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Very little pressure treated lumber is straight, most of it is twisted, crooked, cupped, bowed, etc. If you have just one bad board you got much better wood than most.

Just start at one end and try to straighten it in the process of fastening it down. If you're using screws, it's pretty easy - the screws will pull the deck board into the joist.

Nails will too, but it's harder nailing when the board won't lay flat. If you nail down the side that's in contact with the joist first, then use a clamp from the bottom of the joist to the top edge of the decking, that will pull it down so you can nail it easily without it bouncing all over.

If it's so bad you can't make it work, scrap it or maybe try to return it.

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  • 3
    If you can clamp it down, you can screw it down. If you can't get it to clamp down, return it for a replacement. As such, I'd suggest clamping both ends down so you haven't drilled any holes in it before you return it, if you need to return it. Otherwise all you can practically do is use it somewhere in short sections where the twist is less of an issue due to less distance over which to be twisted.
    – Ecnerwal
    Sep 10 '20 at 11:29
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    It helps to pre-drill the holes so the screw threads won't bite in the decking, or to use special decking screws with a reverse thread on the portion near the head. With normal screws, no pre-drilling, and 2x lumber, there's a limit to how much the screw will pull the decking and joist together, since as the screw turns the threads will pull the joist and the decking up.
    – Phil Frost
    Sep 10 '20 at 13:58
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    PT lumber is actually quite straight when it arrives at the store or on location. It's only after the units are opened and it starts to dry out that it gets ugly. When it first arrives it's so wet that nothing has warped yet. Look for fresh, wet boards when you buy, and install them right away.
    – isherwood
    Sep 10 '20 at 14:56
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    @isherwood then they shrink up on you once they're installed on the deck causing other issues like squeaking decks. Basically there is no good way to use a natural product outdoors without some sort of issue... :(
    – FreeMan
    Sep 10 '20 at 14:59
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Quick 'n Easy

If you find that screwing it down without clamps won't resolve the issue (decking should never be nailed down), make half-depth crosscuts from underneath, centered over joists, at several locations (say every other joist). This will weaken the twisting/bending tendency of the board without unduly compromising its strength as a decking component or affecting appearance.

  • Lay the board in place and mark the joist locations where you'll cut (or use your screw holes as references)
  • Set your circular saw to depth by resting it on the deck board and adjusting the table position so the blade reaches roughly halfway through the board
  • Flip the board, transfer and square the location marks to the underside, and make the cuts

An added benefit to this approach is that further warpage won't result in waviness or bulging in the board. Sometimes when you try to bend nature to your will it fights back, resulting in humps and ski jumps down the line.

When you run screws in at those locations use caution to not run them too deep. They're more likely to pull through the upper portion of the board.

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  • How long should the cuts be? Should there be just one cut in the middle of the board over every other joist, say a foot long and centered with 6 inches on either side of the joist? Sep 10 '20 at 17:03
  • Crosscuts. Not rip cuts.
    – isherwood
    Sep 10 '20 at 17:05
  • Oops, I missed that explanation in your first paragraph. This sounds like a good strategy. Maybe I can make the crosscuts just to the left or right of the screws but still keep the crosscuts over the joists. Sep 10 '20 at 18:39
  • Yes, you could, but you'd want at least 1/2" bearing for each deck board segment. I wouldn't mess with that risk. Just cut at the center.
    – isherwood
    Sep 10 '20 at 18:43
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Start at one end and use screws. It's much easier if you have someone to assist you. Also check out the BoWrench tool. I have used this on multiple projects and it's well worth the cost especially if you are working solo.

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  • Hello, and welcome to Home Improvement. Thanks for the answer; keep 'em coming. And, you should probably take our tour so you'll know the details of contributing here. Sep 10 '20 at 15:06
  • For completeness - cepcotool.com/bowrench.html I'd never heard of it.
    – Criggie
    Sep 10 '20 at 21:46
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Having done this recently I know it's a pain. I bought straight boards but by the time I installed them after waiting for a few weeks for them to dry out, they were warping.

You need to get a few C clamps or something similar. Start at one end and screw the board to the end joist, then clamp the other end and tighten to see if maybe the board is flat on the second joist from the end you just screwed down. If it is, screw it down there. Continue this until the entire board is screwed down. Let it take a few days to do it, the board didn't warp over night so don't expect to straighten out over night. Hopefully you're using stainless steel screws .

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