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Decking Posts Rotting

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  1. #1
    Apprentice (new member)
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    Default Decking Posts Rotting

    Hi,
    Just new to forum and have a decking problem.
    I erected a treated pine deck about 1994 and used H4 treated 100*100 treated pine post directly into the ground encased in concrete. These have been fine till now, as i was checking under the deck and clearing away the rubbish from the concrete/post interface and found some severe rotting in a few posts. This was abviously caused by moisture build up around the base.
    What is the best solution to fixing this problem?
    ( I was thinking of retreating the good posts and building up the concrete to keep the water out .)
    Thanks
    Benny56

  2. #2
    A Member of the Holy Trinity silentC's Avatar
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    Default

    When you're putting posts straight into concrete footings, there are a couple of things you have to observe:

    1. Make sure the footing is a couple of inches above ground level
    2. The top of the footing should slope away from the post on all four sides
    3. Make sure that you don't allow debris to collect around the base of the post

    I would also have painted the bottom of the post and up to 100mm above the top of the footing with some bitumous paint like Ormanoid.

    The ultimate solution is to use stirrups.

    You can probably stop it from getting worse if you build the footing up around the post. I'd also look at replacing any rotten posts with new ones. If possible you could attach them via stirrups and dynabolts to the top of the existing pad, or pour new ones if need be.

  3. #3
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    Default

    As silent c says. Use stirrups. Never really undestood putting posts directly into the ground. If you can get a jackhammer in there and remove the old concrete cut your posts back about 100mm off the ground and slide a stirrup in, blt it and then reconcrete.

  4. #4
    Quick and Rough MurrayD99's Avatar
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    Default

    <TABLE borderColor=#cc9966 cellPadding=6 width="100%" border=2><TBODY><TR vAlign=top bgColor=#cccc99><TD width="29%">Situation
    Low decay hazard
    Moderate decay hazard exposed to weather but not in ground contact
    High decay hazard ground contact (no 50-year durability)
    High decay hazard ground contact (50 year durability)

    </TD><TD width="29%">Timber Treatment
    H1
    H3


    H4



    H5

    </TD><TD width="42%">End Use
    Interior framing, lining, trim
    Decking, bearers, weatherboards, joinery, railings


    Fence posts, agricultural posts, pergola posts


    House piles, deck posts and support poles

    </TD></TR></TBODY></TABLE>

    I know you want a fix rather than advice on what to use - but you'll see H5 is recommended for piles etc - though, frankly, in concrete, I would have used H4.... Maybe your H4 treatment wasn't exactly up to spec....

  5. #5
    Building Designer ausdesign's Avatar
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    Default

    This is an ongoing occurance that I haven't heard addressed entirely.
    Personally I try to steer clear of encasing any timbers in concrete - H5 does better than many.
    Often the concrete is required to give lateral stability to the post rather than support.
    One answer may be to sit the post on a concrete or timber pad, backfill with a small amount of soil to give a drainage layer & then top up the hole with cement.
    Others I've read are to dome the concrete above ground level or keep the concrete below g/l & top with domed clay. Both have the disadvantage that the water can still penetrate.
    Also cutting the post & then not sealing the end is a weak point with treated timbers.
    Stirrups are definitely the answer with low structures or timber treated for permanent water immersion for all.

    Just my bit
    Peter Clarkson

    www.ausdesign.com.au

    This information is intended to provide general information only.
    It does not purport to be a comprehensive advice.

  6. #6
    A Member of the Holy Trinity silentC's Avatar
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    One answer may be to sit the post on a concrete or timber pad, backfill with a small amount of soil to give a drainage layer & then top up the hole with cement.
    The NSW Timber Framing Manual shows one method of dealing with posts in the ground. A small amount of aggregate is placed in the bottom of the pier hole, the post is put in position, then more aggregate is added around the post. The top is capped, presumably with concrete, at or above ground level and sloping away from the post.

    I think the key is to prevent prolonged exposure to moisture, so if you have a self-draining pier like this, you reduce the chance of rot. But I'd still coat the post, no matter what level of treatment.

    I'm not certain of this but I feel you have to make sure that the coating runs a decent height up above ground level as well, or all it really does is seals in any moisture that gets into the post from higher up.

  7. #7
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    Default Thanks

    Thanks guys for your replies...my biggest mistake was not building up the footing into moisture runnoff setup. I do not think the gravel in the base of the hole would have done much as the substrata is all clay.
    Think i will try and treat and build up the posts that are not to bad with concrete...then try and go for the stirrups on the other two.
    I do not think that H5 100*100 post were available back in 94.

    Benny56

  8. #8
    Quick and Rough MurrayD99's Avatar
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    Default

    Quote Originally Posted by benny56 View Post
    I do not think that H5 100*100 post were available back in 94.

    Benny56
    You could well be right. Thing is, where we are the soil doesn't get waterlogged - or not for long over sand and gravel. Even in heavier soils, tanalised radiata fence posts we put in 30+ years ago are A-OK. I'd be upset too about this'all......

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