Pressure treated wood cupping

Discussion in 'In the Garden' started by swaring, 8 May 2020.

  1. swaring

    swaring

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    Hi guys,

    wonder if anyone can help. I started doing some landscaping on my garden last year, doing raised beds etc. I got all my joints perfect, screwed into posts that are concreted in the ground. I have noticed this year certain areas the wood is cupped pretty bad. Placing them bark side forwards or backs didn’t help as they are cupping either way. Please see pics attached. Would a long screw straighten this at all?
     

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  3. Burnerman

    Burnerman

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    I've had great success with these:
    https://www.screwfix.com/p/rawlplug-universal-ffi-frame-fixings-10-x-140mm-25-pack/24697
    However, I ditch the plastic plug and drill a pilot hole where the screw shank is to go - but first I drill clearance through the cupped timber.
    I appreciate that it isn't the best practice to screw into end grain, but the length of these things overcome that - they have also the advantage that you can tighten them with a 1/2" drive socket.
    Two per corner should be fine.
    John :)
    Apologies if there is a link failure....screwfix 24697.
    J.
     
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  4. conny

    conny

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    Link puts you in a queue but if you go direct to SF site and just put in Johns code number it comes up instantly.
     
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  5. swaring

    swaring

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    Thanks so much I’ll give these a whirl. Do I just fill the hole afterwards and paint :)
     
  6. swaring

    swaring

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    They are thick 50mm boards. Half thickness of a sleeper. Would a screw be able to tighten these. John what thickness wood have you had success with please?
     
  7. Burnerman

    Burnerman

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    I've used these things for fairly heavy duty stuff, here's something to ponder.
    The entire fixing is 175mm long, and is based around 10mm diameter carbon steel which is plated to prevent rusting (looks like cadmium to me). I discard the plastic plug as we are going into timber.
    The hexagonal head is 13mm which is a handy socket size, either 3/8" or 1/2".
    The fixing has 110mm of unthreaded shank - then the thread starts for the rest (60mm).
    So - if you want the hex head visible, drill through both boards at around 8mm. continue this drilling into the second timber, say another 50mm or as far as the drill will reach.
    Now, drill the first timber only at 10.5 - clearance for the shank of the fixing. Locate the fixing with a socket spanner, don't fully tighten until the other one is in too.
    If you want the screw head to be hidden, drill a 20mm hole with a flat bit for 15mm or whatever to form a counterbore, follow with the 8mm tapping size and then finally with the 10.5 clearance drill.
    Maybe you could have a practice run first? Either way, be lucky! Treat all of the timber heavily - wet ground will finish it off sooner than you think!
    John:)
     
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