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Spacing between decking boards

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  1. #1
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    Default Spacing between decking boards

    Is 2mm enough spacing between 90mm decking boards? I started off with 2.8mm, but have reduced it down over a few coarses so I can fit a whole board in at the end rather than having to rip one.

    Have I made a mistake? I'm happy to pull them up and put them down again at the correct spacing if so...

  2. #2
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    2mm is a bit narrow, the boards will butt pretty hard when they expand

  3. #3
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    yep, too small I reckon. I space my 90mm merbau at 5mm because that's what the BCA required in bushfire prone areas (dunno if it still does). 5mm looks good. I reckon you'll end up with all sorts of crap building up between the boards too.

  4. #4
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    If its the usual merbau which is not fully seasoned you should be ok The gaps will only get wider.
    regards inter

  5. #5
    Old Chippy - 4K Club Member
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    Quote Originally Posted by intertd6 View Post
    If its the usual merbau which is not fully seasoned you should be ok The gaps will only get wider.
    regards inter
    Until they get saturated through a very wet season - shrinkages is the norm, but a wet season can see considerable swelling even in coated boards so 3mm is my minimum.

  6. #6
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    I suppose it may depend on the type of material you use.
    When I purchased my treated pine timber from a reputable pine place they told
    me a nail width in between and 6 months later no problems.

  7. #7
    Old Chippy - 4K Club Member
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    Quote Originally Posted by nww1969 View Post
    I suppose it may depend on the type of material you use.
    When I purchased my treated pine timber from a reputable pine place they told
    me a nail width in between and 6 months later no problems.
    So was he suggesting a 1mm, 1.5mm , 1.8mm, 2mm, 2.88mm or 3.2mm diameter nail? I have used a 75mm 3.2mm nail driven through small blocks as spacers when my bespoke spacers were not with me. All timber absorbs water and loses water - and expands and contracts accordingly. If the decking is tight or has too small a gap and the timber gets very wet and swells something has to give.

    I've seen decking so well attached to joists and bearers that the swelling after much rain combined with very very wet soil has lifted the posts out of the ground as the timber twists and turns to try to move. That's extreme and I've sen it only twice - but it is common to see twisted and lifted and cupped decking because too little space has been allowed between boards. Much less a concern in covered areas than on exposed decks. Often decks are laid in summer and then the problem arises with autumn/ winter rains. But highly variable even with the same species.

  8. #8
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    If the decking is Merbau its shrinkage is around 2% from green which is just about how it is sold, even if it was fully seasoned & gained back all it moisture to the cell walls it wouldn't expand over 2mm. Now if the decking is seasoned Australian HWD you could be in for trouble as most of it is around the 6% + shrinkage mark.
    regards inter

  9. #9
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    That's as may be, but I have seen merbau expand to fill and distort when only a 2mm gap . . .
    Advice from me on this forum is general and for guidance based on information given by the member posing the question. Not to be used in place of professional advice from people appropriately qualified in the relevant field. All structural work must be approved and constructed to the BCA or other relevant standards by suitably licensed persons. The person doing the work and reading my advice accepts responsibility for ensuring the work done accords with the applicable law.

  10. #10
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    Quote Originally Posted by Bloss View Post
    That's as may be, but I have seen merbau expand to fill and distort when only a 2mm gap . . .
    That could be definately possible for fully seasoned merbau, but the stuff they are selling now shrinks in width & sometimes length & on a couple of jobs have been specified with non mitred corners so the joints don't open up.
    regards inter

  11. #11
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    All the decks Ive done in the last 5 years - all with merbau, have all shrunk - a lot. I started using 4 mm as a spacer on my own decks and those gaps 7 years later are 6 mm +.( could be in trouble if the wife rips out the stilletto's) Now I use 2.8 mm nails and its all good.

  12. #12
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    2.8 nails through a block is what I have used for yonks. My point was not that merbau doesn't shrink, but that a 2mm gap if/when it then re-saturates after some lengthy wet weather (if exposed of course) is not a good safety margin IMO considering the damage that can occur if there is expansion - that 0.8 to 1mm difference can make all the difference. It's not a die in the ditch issue - just my single experience - and from non-drought times. In many parts of Oz various timber structures will see effects of moisture not before experienced if the spring continues as wet as it has been this year.
    Advice from me on this forum is general and for guidance based on information given by the member posing the question. Not to be used in place of professional advice from people appropriately qualified in the relevant field. All structural work must be approved and constructed to the BCA or other relevant standards by suitably licensed persons. The person doing the work and reading my advice accepts responsibility for ensuring the work done accords with the applicable law.

  13. #13
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    I reckon the 2.8's are the go. The only downside is waiting for them to shrink as its a real PITA to keep / get crap out of the gap. Much better when are about 4 mm after a few years.

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