I want to mate two 2x6s pressure-treated boards (span = 8') so that I can use them as a beam for my ground-level floating deck.

  1. Should I use a construction adhesive? Anything special given that the boards are pressure treated?

  2. What should I use: screws, bolts?

  3. What is the recommended spacing between screws? how many screws at each mark?

  4. Screw / bolt length?


[Edit] For clarification, by mating I mean joining them together such that two 2x6s become a single 4x6.

  • Mate means what? Extend length wise? Sit side by side? Jul 18, 2018 at 19:09
  • @TheEvilGreebo side-by-side e.g. two 2x6 become 4x6. Jul 18, 2018 at 19:10
  • 1
    Ok the term generally used in my experience is "sistering" Jul 18, 2018 at 19:11
  • 1
    2x6s aren't suitable for a beam at any span over about 3 feet, btw. They aren't even used as common joists.
    – isherwood
    Jul 19, 2018 at 3:00

1 Answer 1


I usually nail them together. Construction adhesive won't be enough. You could use screws also.

For spacing I usually start by making sure the crown is going the same direction and at one end put 2 in within a few inches top and bottom, then at 6" away from those put another nail on the top an inch from edge another 6" one an inch from the bottom another 6" another at top and repeat until close to the end of the board 2 like the start.

If your lumber has different bow in each board this can be pulled to match as you nail make sure to check that they still match at the loose end after each nail and it is usually easy to keep them even.

  • What would be the nail / screw length in this case? Thank you, Ed! Jul 18, 2018 at 23:40
  • 1
    2-1/2" deck screws or 12d galvanized nails. You could use 16d nails if you angle them so they don't protrude.
    – isherwood
    Jul 19, 2018 at 3:03
  • Agree with both sizes if I use 16's I try to angle them in kind of a v pattern it makes it a bit tougher.
    – Ed Beal
    Jul 19, 2018 at 13:10

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