Mahogany Exterior Deck Cupping

Discussion in 'Other Home Decorating & Remodeling Projects' started by Mike Antonetti, Dec 16, 2017.

  1. Mike Antonetti

    Mike Antonetti I Support TFP Senior Member

    I assume all the minimum standard apply for all wood, ventilation underneath,spacing,gaps between 5”? boards, which on this particular deck is probably not met. The conversation went like this- Nice Deck, what kind of wood? he says- Mahogany, “it still cupped”. (Said with disappointment)

    I’m guessing since the approx 20x40 free form deck the homeowner assumed by using top quality material that the deck wouldn’t cup. I’ve seen cupping in many decks, this particular one was holding melted snow in the concave planks on Long Island. So ‘if’ getting plastic deck would avoid this situation it beats the best hardwood available.
  2. kylenelson

    kylenelson You'll find me on the floor I Support TFP Senior Member

    It’s still wood....I lik concrete better. Stays cooler and low maintenance
    • Agree Agree x 1
  3. Jeff Short

    Jeff Short Veteran Flooring Retailer

    A friend of mine built a deck around his above ground pool several years ago. We were talking before he built it, and he said he was going to use wood. I told him he should look into Trex composite decking, which he wasn't familiar with. He looked into it, used it, and to this day occasionally says to me that it was some of the best advice he ever got.
    • Agree Agree x 2
  4. kwfloors

    kwfloors Fuzz on the brain Charter Member I Support TFP Senior Member

    Maybe there is a natural cup to the planks that should go down instead of up. We have lots of decks with it up here and I have never seen one cupped. Strange.
    • Informative Informative x 1
  5. Steve Olson

    Steve Olson Hardwood/Laminate Guru Charter Member Senior Member

    Bark side up on those deck planks?
    • Funny Funny x 2
  6. Dan Schultz

    Dan Schultz Certified Wood Floor Inspector Charter Member

    Could be. Wood shrinks more towards the outside of the log.

    Long Island, eh? Sounds like a very humid area. If this deck gets a lot of sunshine that could cause the top side of the boards to dry more.
    • Like Like x 1
  7. Mike Antonetti

    Mike Antonetti I Support TFP Senior Member

    Some family members do not get the requirements for exterior wood. I believe sun beating on one side will do that. So I’ve come to the realization that what’s on top needs to be what’s on bottom, a balance of moisture otherwise wood will move disproportionally one side verse the other.

    Something I don’t get is how coatings affect the movement of cupping and crowning. Sealers and urethanes usually go on top, minimizing absorption from one side. Bamboo may be coated top and bottom but I’ve seen multiple cupping issues with it.

    I looked at a basketball court a few years after install, it has forced ventilation underneath and still looks brand new, somehow they are properly maintaining it.
  8. Floored by Newman

    Floored by Newman Floored by Newman

    When I lived in Wyoming I played with this. I installed a deck at home.Moisture under 10. Plain # 2 common. Bark up and down. Bark up cupped as a arch. Bark down cupped as a valley. Water sealant did not help anything... Normally one should install bark up or down?Still confused...
    Last edited: Dec 30, 2017
  9. Floored by Newman

    Floored by Newman Floored by Newman

    Good thing I don't professionally install decks!
    • Like Like x 1

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