Decking expansion gaps

Discussion in 'Carpenters' Talk' started by masonst0rm, Aug 3, 2006.

  1. Mr. Handyandy

    Mr. Handyandy Screwfix Select

    You're never gonna get that. Why would water run off the edges? Most of the time there'll be a slight cup(the wood previously drying and shrinking on top first/fastest), and with no grooves, that water will stay there underfoot until it dries out or runs away/soaks in.

    Fact is(with a 7mm groove) you can have 3.5mm of rain and NONE of it will lie on the raised part. And if you have that much, it will be pouring off the ends all the time, keeping it below the raised parts.

    Heaven opening doesn't count in any case.

    Pretty grooved design is not designed to be hidden underneath.

    Mr. HandyAndy - Really
     
  2. chippie244

    chippie244 Super Member

    The cupping depends on the timber rings.
    If the rain isn't going to run off the sides how does it run into the grooves.
    You just aren't getting the fact that there is no extra fall in the grooves.
     
  3. wuddy

    wuddy Member

    Sorry I dont fit the diy grade stuff with grooves in
    New boards will only shrink not swell unless they are kilned
    Try this link
    http://inspectapedia.com/BestPractices/Deck_Board_Spacing.htm
     
  4. Mr. Handyandy

    Mr. Handyandy Screwfix Select

    No. The cupping does not depend on the rings. The cupping depends on which dries faster. 99 times out of 100 there will be a concave cup rather than a hump, because the underside of the board will always be wetter. That's why they cup.
    Take a cupped board out, turn it over and very soon it will be lying flat again. Don't diss it, try it.

    As I said before, just how much water can build up on any raised parts before it falls off into a groove? Not a lot.

    While you are at it, chuck a bucket of water on grooved decking. How much is sitting on top of the raised parts? Possibly none. It's all in the grooves.


    Mr. HandyAndy - Really
     
  5. chippie244

    chippie244 Super Member

    Utter, utter ****.
    I worked in a sawmill for 3 years, I know how wood cups and shrinks.
    If the water can fall into a groove on its slow journey down its 4M journey why wont it fall off the edge of the board without a groove?
    What is happening to the water in the groove, it's growing moss.
     
  6. Mr. Handyandy

    Mr. Handyandy Screwfix Select


    Look, it's not my problem if you haven't fitted the darn decking properly to allow the water to run away. The grooves should not stay wet for long after the rain has stopped. If yours does, it's fitted wrong.

    Go turn a bit of cupped decking over and WATCH IT straighten out. Then tell me it's the direction of the rings!

    I told ya. Don't diss it til you tried it. I HAVE tried it. I've seen it, done it.

    I have my own decking(this one been down 8 years). I have NEVER had moss grow in the grooves. That is a fact.

    Mr. HandyAndy - Really
     
  7. chippie244

    chippie244 Super Member

    I will let you have that cupping can be dependant on growth rings and moisture but with the grooves to the bottom the boards will cup centre up when wet and throw the rain off to the sides.
    I don't have decking!
     
  8. Mr. Handyandy

    Mr. Handyandy Screwfix Select


    I already told you that if you take a cupped board(grooves up, cupped up at edges) and turn it over flat side up, it will flatten out, so that is not cupping centre up.

    Mr. HandyAndy - Really
     
  9. chippie244

    chippie244 Super Member

    If it is moisture that is making the wood cup the wet side will expand and that is the top side so it will cup centre up and it will shed water to the side.
    Reread your post. Why would the underside be wetter especially if you had laid the decking the right way round with the drip on the bottom?
     
  10. chippie244

    chippie244 Super Member

    You are prooving my point here.
     
  11. Mr. Handyandy

    Mr. Handyandy Screwfix Select

    No I'm not. You say flat board cups up in centre.
    I say if grooved cupped board(edges up) is turned over(that gives flat board cupped up in centre), it will flatten, not to be cupped up.

    And the bottom will almost always be wetter that top for drying out purposes. More air and sun will always dry the top first, making it shrink at the top first, making it cup up at the edges.

    Mr. HandyAndy - Really
     
  12. chippie244

    chippie244 Super Member

    When it is wet it is wet and will cup centre up and shed the water, if it was dry it wouldn't matter.
    A dry board will cup according to the growth ring, a wet board will cup wet side up.
    What gets wetter, the top of an umbrella or the underneath?
     
  13. Markyboy34

    Markyboy34 New Member

    When timber dries out the growth rings straighten, that's why when choosing timber for a decent job, the rings should be short, between the top of the timber and the bottom, but if they are width ways, and sag like a piece of string hung from left to right, and nearly touch the bottom, when this dries out or seasons properly, the rings will straighten and the timber will cup down when the rings have straightened, the only way to straighten this when cupped, is to turn it upside down , put a four inch screw in each side and watch a split emerge down the middle, short rings and straight rings in an end grain means better quality, as the timber should nt move as much if at all . .
     
  14. Mr. Handyandy

    Mr. Handyandy Screwfix Select

    If the umbrella wasn't waterproof, and the bottom had less air, light and direct sunshine, then the underneath would be wetter for longer. But an umbrella doesn't have those properties, does it ?

    Mr. HandyAndy - Really
     
  15. chippie244

    chippie244 Super Member

    What way does wood cup when it is wet?
     
  16. Mr. Handyandy

    Mr. Handyandy Screwfix Select

    Wet boards generally have no right to cup at all. It is the drying out that makes them cup.

    And as I said many times, turn a board over, and it will cup the other way, and straighten.
    That makes a complete mockery of ring theories.
    Wet expands, dry contracts. That's why it cups.
    The bottom(whatever flat or grooved) will dry out slowest.

    Mr. HandyAndy - Really
     
    Markyboy34 likes this.
  17. chippie244

    chippie244 Super Member

    A wet board will cup centre up and shed water, what it does when it is dry doesn't matter because it is dry.
    The grooves underneath are the drip, you know what a drip is don't you.
    The bottom will not get wet till the water has soaked through from the wetter, top, side.
    The ring thing isn't a theory, it's how wood works.
     
  18. Mr. Handyandy

    Mr. Handyandy Screwfix Select

    But when the bottom is wet, it'll stay wet a lot longer, and the top will dry out very quickly, and will cup up at the edges. Boards that cup up in the centre should have screws in that line, just like most decking boards will have 2 screws one near each edge(to help stop it cupping up at the edges)common sense really!

    How many decking manufacturers recommend laying decking grooves down?

    Mr. HandyAndy - Really
     
  19. chippie244

    chippie244 Super Member

    What are you talking about man, a grooved bottom will stay wet longer, despite not getting wet because the water will fall off at the first drip?
    A board that cups centre up when wet is good because it will shed water.
    You're just arguing for the sake of it
     
  20. Mr. Handyandy

    Mr. Handyandy Screwfix Select


    Take a board up man. Look under it. Then come back and tell me it's drier than the top when the top has started to dry out.

    Until then, you can't comment.

    Mr. HandyAndy - Really
     

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