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OT: Fence post coating

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  • OT: Fence post coating

    I am building a heavy duty treated wood fence, and many of the posts will be set in concrete. many people have told me that if you set a treated wood post in cement, it will dryrot and break off in less than 10 years. I live in MN, so there is plenty of moisture. This page, says to wrap the post in tar paper. any one have a better idea?

  • #2
    Make sure the fence post is very dry..low moisture content..this maximises the uptake of the preservative..
    soak fence post for one week in a mixture of old engine oil and creosote.
    when concreating it in .
    1.make sure the concrete comes up higher than surounding soil.
    2. make it rise up towards the inside shallow cone profile to the concrete .this will shed any water and discourage puddleing.
    two weeks after a slight gap will develope between the post and concrete as the concrete shrinks.....flash the gap off with silicon sealent.
    if your going to use other wood treatments make sure they are all oil based (white_spirit based)
    the water based ones are not much cop.
    all the best....mark

    [This message has been edited by aboard_epsilon (edited 06-19-2005).]


    • #3
      Concrete should never touch wood and I remember a note somewhere to never use automotive oil, it will eat and decay wood.This is why it is not a good thing to oil you gun with engine type oils if they have a wooden stock. Concrete gets stronger with age and that is because it can constantly wick moisture which improves its strength. Moisture however rots wood. Put galvanized steel post in cement but not wood My method is to dig a hole to a depth of 4' and about twice the diameter of the post. A 6" pole gets a 12" hole. Set the pole in the hole and backfill with 3/4" clear gravel with about 3" or 4" on the bottom under the post. Pack it as you go. Moisture will not remain in the gravel unless it is a post located were there is a high water table. I have pulled old posts out of gravel and they are like the day they went in the ground. Frost can grab concrete and lift your posts but not gravel. My two cents worth.


      • #4
        I see someone here (Northwest Missouri) is marketing steel legs to cement into postholes to bolt treated pole barn legs to. No doubt many CCA pole barn legs have begun to rot off. I've seen CCA fence posts rot in concrete.


        • #5
          Unless you have old-time "peaches and cream" cedar, concrete seems to destroy the wood. I don't know why.

          I set my western red cedar direct in dirt 10 years ago, and they are still good.

          Treated pine set in concrete rotted noticeably at the neighbors in 3 years. It is still standing, sort of, but it is obviously failing.

          The 30 year old P&C cedar in concrete is nearly as good as when it was put in.

          Keep eye on ball.
          Hashim Khan


          • #6
            I am in the process of setting a number of 6x6's of pt lumber in concrete.
            I tapered the part to go in the concrete and have coated it with epoxy (asfar as it is in the concrete.) If the wood shrinks it will sit further down in the socket.The expoxy should stop water soaking the underground wood .

            Might work.

            The British miliatary(in the mid 1800s) used to set exterior posts into a bronze socket which then went into masonry -copper stopped the rot.Mind you they used some nice teak and real pitch pineat the time much better than any pt lumber.

            maybe if you had some copper sheet and wrapped the post it might worklike that.


            • #7
              Hi Happy:

              I’ve built and replaced a buncha fences over the years and based on that experience here’s my advice: If you want fence posts that will outlast you and probably your grandchildren as well, get yourself some �Ground Contact’ 4 x 4s and set them in concrete about two feet deep – just slowly pour regular ol’ dry-mix around the post and add water as you go. This is not your typical green pressure-treated material; it’s dark brown, almost blackish in color (about like cutting oil) and will send any rot-causing soil bacteria within six inches to an early death. This is truly a great material for the application but a few caveats should be observed: 1) Put only the factory (uncut) treated end in the ground; 2) wear a dust mask and face shield when cutting-off the tops to avoid airborne poison exposure; 3) wear gloves when handling (this is some nasty stuff) and dig-out any splinters immediately before they fester; and 4) I would avoid using this material within several feet of any edible garden produce.

              Hope this helps.

              Kind regards,



              • #8
                Been following this BB for awlie as an observer- good stuff. Live up in the GWN and we helped develop a product at work called Cobrarod. You drill a hole down at an angle into the post and place this stuff in as an insert, it supposedly draws up moisture and almost petrifies the post. Power utility companies up here are using it to extend pole life. They claim it will extend a pole's life 20-80 years depending on conditions.
                Opportunity knocks once, temptation leans on the doorbell.....


                • #9
                  I have about a mile of fence. It's 4 strand barb wire and the posts are treated pine driven direct in the ground. The standard treated post here is the green treatment which is copper napthanate. If properly done it will last around 25 to 50 years here. I also have posts set directly in concrete which I hand treated with CN and they are just fine after 20 years. The only thing better is a creosote full treat which is what the railways use for cross ties.

                  We do have one advantage here which is that the ground is frozen solid six months of the year. That automatically doubles the life of any post as there is nothing biological going on in frozen soil.

                  One thing to watch out for is the light brown wood treatment. I was speaking to the building inspector the other day as I need to replace my sundeck. He informed me that the light brown preservative is extremely corrosive and will eat ordinary electroplated galvanized fasteners in a matter of weeks or months. That applies to fence staples too.
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                  • #10
                    Spend the extra $ and use redwood.