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Wood post in concrete

I have nearly completed a triangle pergola in my back garden with pressured treated wood, I used post mix and concrete to fix my 4x4 post into the ground with about 1-2 inch of gravel at the bottom and around the post . I am a bit worried now that I have done it totally wrong and it going to rot in no time image.  

I don't think I added enough drainage, and just before I added post mix I hammered the posts into the ground a little bit to make them more secure, I didn't think at the time but the posts are probably sat in a wet clay now. Does concrete make wood rot faster as well?

I don't know what to do now? pull it down and try and fix it some how. How long do you think it would last if I just leave it? The project probably cost me about £110.



  • WelshonionWelshonion Posts: 3,114
    If you decide to start again you can get metal cradles to hold wooden posts off the ground to stop them rotting. Or you can use Metaposts.

    But your current method sounds good enough if you have used pressure treated timber, buried it deep enough and you are willing to apply wood treatment regularly.
  • Mark 499Mark 499 Posts: 380

    The post will only rot at ground level, it does not matter what you put in the bottom of the hole. A pressure treated post will last around 10 years. if you use metposts the post will still rot they just make it easier to replace & in my opinion they look horrible.

  • ObelixxObelixx Posts: 30,006

    In my experience metposts are less secure than concrete too.  All our fence and trellis posts held by metposts are at a drunken angle now after a series of gales over the years but the concreted ones are vertical.    Some of the posts have been there 20 years and none has rotted yet.

    Vendée - 20kms from Atlantic coast.
    "We don't stop playing because we grow old; we grow old because we stop playing." - George Bernard Shaw
  • YviestevieYviestevie Posts: 7,063

    Perki, that's how my arch was put in by hubby, but funny enough I was thinking of putting another one in further up the garden and was asking myself the same questions.  I wondered whether hubby had cut a few corners but it sounds as if he did the right thing.image Oh me of little faith.

    Hi from Kingswinford in the West Midlands
  • PerkiPerki Posts: 2,490

    So they probably be ok for a while, enough time to get the wisteria covering it. It is windy at the top of the garden I don't think them metal post holders would hold, pergola are very top heavy. 

    I got another question, I haven't concreted all the way to ground level,  about 5 inch to ground level. I was going to stain the wood with ronseal 5 year guarantee stain and fill it back in with soil, or do I concrete it to ground level or gravel? 

  • ObelixxObelixx Posts: 30,006

    We dig a hole 2' deep and 3 or 4 times as wide as the post then drop some gravel in the bottom then stand the post on that and pour in dry concrete mix to soil level.   Add water and one of us mixes it up with a garden fork while the other uses two spirit levels to make sur ethe post sets vertical.  

    We use quick setting concrete mix.  We do not treat the posts as they're already pressure treated and we want them to fade gracefully.

    Vendée - 20kms from Atlantic coast.
    "We don't stop playing because we grow old; we grow old because we stop playing." - George Bernard Shaw
  • PerkiPerki Posts: 2,490

    I do exactly the seem thing  obelixx except not to the soil level

  • All sounds good to me. The posts are pre treated now day,s sit back and enjoy all your work this summer!!!!!!!!!!.image

  • I set the posts in a decent sized hole and back-filled with a dry concrete mix and just left them to set from the natural ingress of water/damp from the soli. I had nailed 2 supporting pieces at 90 degrees to keep them upright. To beat the problem of rotting at groung level, I tamped the concrete mix flat at ground level to provide a base on which to lay one or two courses of bricks around the posts' base - in the hope that this will keep away the rotting action of the soil, even though the posts are treated. The treatment is, by the way, a vacuum treatment rather than pressure, and it's a chromium/copper/arsenic mix, all heavy metals.

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