deck warping

Discussion in 'Carpentry and Woodworking' started by skip widney, Jul 17, 2009.

  1. Jul 17, 2009 #1

    skip widney

    skip widney

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    GC installed a pressure treated deck 3 weeks ago. Today it is warping and dipping and looks horrible. The corners of the railings are 1/2 inch apart already, and when it was installed, it looked perfect. He assured me that within 6 months, it would

    "settle down and be straight like it looked when he installed it". Doesn't sound right, what do you think???
     
  2. Jul 18, 2009 #2

    Nestor_Kelebay

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    Has it rained a lot since the deck was built.

    I would educate myself about wood shrinkage and warping.

    Go to the Roofing and Siding forum and read the tread entitled "Flat Roof Exposed Beams...". That will get you up to speed on why you have gaps in the railings.

    And, the warping boards are addressed in the University of Massachusettes publication entitled "Decks: Nail boards bark side up or bark side down" (or something similar to that).
     
    Last edited: Jul 18, 2009
  3. Jul 19, 2009 #3

    Nestor_Kelebay

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    Skip:

    Here's a link to that paper discussing wood warping during drying:

    UMass Amherst: Building Materials and Wood Technology ยป Do I Lay Decking Bark-Side Up or Down?

    Basically, if a living tree had a round trunk and all the growth rings were concentric, then no matter where you cut a board out of that tree trunk, the growth rings would tend to straighten out as the wood in that board dried out.

    So, if you cut a board horizontally from the top half of the tree trunk, as that wet wood dried, the board would cup upward (concave up) so as to hold water on it's surface as it dries out.

    Similarily, if the board was straight when it was dry, then wetting it will cause it to warp such that the growth rings form a smaller circle.

    Theoretically, lumber isn't supposed to be cut to size until after it's kiln dried, and "kiln dried" means a moisture content of 19 percent. But, you need wood to be truly dry before you can pressure treat it well, so maybe your pressure treated lumber was straight when it was installed, but warped when it got wet. Typically, tho, once wood is nailed into place, it doesn't warp. Mechanical fasteners like nails and screws are plenty strong enough to keep the wood from twisting or bending, and once it's dried in place, it'll retain that same shape.
     
    Last edited: Jul 19, 2009
  4. Sep 29, 2009 #4

    DeckPro

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    pressure treated lumber is great for the flooring and if you slam it together tight when first installed. It will shrink a 1/4" to 3/8" in just a few weeks, but generally should NOT be used for the railing because of the shrinkage and warping.. cedar or redwood are a couple good choices for the railings especially on the top cap, if you have one...
     
  5. Sep 29, 2009 #5

    kok328

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    Should have went with a composite decking material like Veranda - no warping, cupping or cracking and is technically termite and maintenance free.
     
  6. Nov 14, 2009 #6

    Just Do It

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    We do wood restoration work, it's 99% of our business. All wood will go through a shift, it will dry, it will crack, it will warp and cup and so forth over time. Most uneducated builders will tell you to let the deck age for a period of time before cleaning and sealing it. This is simply bad advice. The USDA Forest labs will tell you, that ideally you should clean and seal the PT deck within two weeks of building it. Now having said that, will your deck be ruined if you don't? No. But care and maintenance begin when you build, not a year down the road. What kind of fasteners did the GC use to attach the boards? Nails or screws? If the floor was nailed, you might consider adding screws now to help stave off additional warping. I hate seeing people pay good money for a deck only to have a builder use nails. Cheap, cheap, cheap.....

    Beth
     
  7. Dec 3, 2009 #7

    Launchpad

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    I've always put deck boards down with what would be the "Bark side" down. Reasoning was as the board dried it would be unable to curl or wrap, especially if it was screwed down.

    I have no idea if that is actually true, I just remember my dad always getting real upset and a sharp pain in my butt everytime I put them down the other way. I'm gonna go back and read the links Nestor posted. I'm hoping Pa was wrong so I can drive 300 miles south and push him off that blasted porch....

    Oh the memories :(
     
  8. Dec 3, 2009 #8

    Launchpad

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    Thanks Nestor! I now have a scientific study to prove the old man was wrong!

    Great link.
     

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