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Thread: Douglas Fir Posts - Movement/Cracking

  1. #1
    Join Date
    Sep 2016
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    Shenzhen, Guangdong
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    Douglas Fir Posts - Movement/Cracking

    i am building a climbing frame for a school and will be using 6x 300mm diameter, 4m long Douglas Fir posts for the load bearing legs.

    The lumber yard I am buying from is a long way from where I will be installing the climbing frame and there is a massive humidity swing between the 2 locations. Currently they are finished/turned and stored inside in a 30% humidity environment. My shop is 90% humidity (I know - terrible, but its a 15,000sqft shop and at the moment I can't afford to climate control the whole thing).

    Can I fight it? I will have the logs in my shop for 1 month for construction/assembly but I am worried that this will be enough time for cracking to appear before I can get the installation erected on site. Cracks appearing after install I can argue - getting sign off on cracked posts on install day is another story. The posts will have to settle to their new environment over time I know but I need a way to slow the process down as much as possible.

    If I were to douse them in a sealer the moment they arrive in my shop can I arrest the moisture absorption sufficiently to prevent cracking? I could ask the lumber yard to seal them before they leave but that would be an additional cost I could do without.

    Any tips/advice would be gratefully received.

  2. #2
    Join Date
    Mar 2003
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    The high humidity in your shop may well work in your favor. Cracks are caused by water leaving the lumber, so the lumber shrinks. The shrinking causes the cracks.

    Have you seen the turned logs? They might be cracking while they're sitting at the lumberyard. If they're basically whole tree trunks, they include the trunk's pith. It is nearly impossible to dry a beam or a trunk with an included pith without cracks.

  3. #3
    You will probably have sharp grain popping up like razor blades on the heart sides. Paint will not prevent that.

  4. #4
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    I know you don't want to hear this but children climbing on a wooden structure seem to be a bad idea due to splinters. Maybe things are different in China. You should look at some other wooden climbing frames before you proceed.

  5. #5
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    Quote Originally Posted by Tom Bender View Post
    I know you don't want to hear this but children climbing on a wooden structure seem to be a bad idea due to splinters. Maybe things are different in China. You should look at some other wooden climbing frames before you proceed.
    Oh címon, kids have been climbing in trees since forever.

  6. #6
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    Quote Originally Posted by Jamie Buxton View Post
    Oh címon, kids have been climbing in trees since forever.
    Very true, however trees have bark, timbers don't.

    I've never had a sliver from bark however I've had a couple of doozies from climbing timber..........Rod.

  7. #7
    Easiest sure fix to avoid splinters is glue a piece of cloth on the bad sides,with Tite bond 2 and then paint.
    Last edited by Mel Fulks; 05-08-2019 at 3:45 PM. Reason: spelling

  8. #8
    Join Date
    Sep 2016
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    Shenzhen, Guangdong
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    Thanks for all the advice folks.

    They have arrived - see pics.

    Some minor cracking but nothing to worry about yet (I presume). Plan now is to run them over with the belt sander to take the worst of the roughness out, then add an outdoor wax oil. Have used this stuff in the past (don't ask me the name - its a Chinese brand but comes recommended from a desk builder friend).

    Project's not due to leave the shop for another 2 months so can keep an eye on any movement.

    As for splinters. You are right - they are a concern but still - if we can't make climbing frames out of wood then what are we left with? There are enough blow moulded plastic monstrosities in playgrounds already! (The school I am selling to have agreed to a twice yearly maintenance contract so hopefully we can catch most of the bad splinters before they are a problem)

    364364555.jpg805649308.jpg1790316711.jpg2115470340.jpg

  9. #9
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    Sep 2016
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    Shenzhen, Guangdong
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    (ref wax oil - meant to say: Have coated dozens of outdoor projects with this stuff over the past 4 or 5 years and it's excellent. Have a picnic bench that's been in direct, tropical sunlight/torrential typhoon rain/temp ranges from 4-40degrees and humidity swings from 40-95% for near on 3 years now and its still flawless. Sure - it's a bit rough to the touch these days but a quick sand a re-coat is all it needs). Pic attached (though doubt it sells outside China....?)
    1461096752.jpg

  10. #10
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    Bill, your use of Douglas Fir makes me curious. You're in southern China, practically in the tropics. I think of that part of the world -- Viet Nam, the Phillipines, etc -- as growing lots and lots of trees. However, instead of getting lumber from there, you've chosen doug fir, which comes from the US -- many thousands of miles across the Pacific. What's up with that?

  11. #11
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    Jamie - It comes from Russia (as does a staggering amount of the softwood used in China).

    But

    On a wider point: My customers are private schools in China. They are wealthy folk and have a (in a lot of cases incorrect) mindset that 'made in China' is not a good thing. There are some spectacular craftsmen doing amazing things over here but still the mindset of 'import everything' lingers among the 1%ers. Sounds ridiculous when talking about wood I know but still: When pitching for a job, being able to say 'imported wood' is a selling point.

    Also - of course - Douglas Fir (in my opinion) is a brilliant outdoor furniture wood. A great balance between workable/finish-able/can take a knock/won't blow the budget.

  12. #12
    Join Date
    Apr 2006
    Location
    Woodstock. Ont.
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    196
    Thanks for the post. Very interesting to see how people in other parts of the world think.

    Brian

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