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I'm geting ready to install a couple new wooden privacy fence gates on the sides of our house. One of my co-workers suggested to wrap the 4"x4" with plastic stretch wrap around the 2' part that will set in the concrete. He had heard that the plastic wrap will keep the lime in the concrete from eating into the wood over time.

Has anyone heard of this or what do you think?

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I've never heard of that and I think your co-worker is a little crazy. –  DA01 Apr 27 '12 at 20:10
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I've tried wrapping the submerged part of the post in Blueskin foundation membrane, including the butt end. I think this should work excellently, so long as the Blueskin rises above the ground/concrete level, and doesn't peel back from the sun.

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There are commercial products on the market designed for exactly this purpose.

One example can be found at http://www.postprotector.com, which manufactures a plastic sheath for 4x4 posts, intended to be buried in the ground.

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While there's nothing wrong with the link, it would be best for you to briefly summarize the linked article so that the information is visible here. –  Chris Cudmore Aug 22 '12 at 17:57
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We're looking for long answers that provide some explanation and context. Don't just give a one-line answer; explain why your answer is right, ideally with citations. Answers that don't include explanations may be removed.

This is a horrible idea IMO. Check out The Fence Bible from you local library. The cement does not rot your posts, the moisture does. Concrete holds moisture. If you don't allow the concrete to wick moisture out to its surrounding dirt, it will rot your posts quick.

I think the best way to do posts is to use just gravel, no concrete. Tamp every 6 inches and you could get it as solid as concrete and this would keep you posts as dry as possible. I was going to do this for my new house, but I decided to use aluminum fencing to avoid the issue entirely.

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This is what I like, or you can use class 2 base rock, but we have no clay out here. –  dbracey Aug 21 '12 at 20:21
    
Major work compared to just pouring bags of quickrete and hosing in some water, but so many advantages: drainage, post removal... –  Evil Elf Aug 22 '12 at 13:03
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If what I am thinking your plastic wrap is, I think it is too thin and would probably be destroyed on installation.

I covered the same area in roofing tar and they have been in for over 25 years. I came up about six inches above ground level. It's been through earthquakes and high winds and the posts have never been replaced. My next door neighbor did creosote and he has had no problems either.

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Most concrete and cement these days do not contain lime. When it contains lime its called Limecrete and generally it is used as a type of mortar for older buildings. Anyway If you wanted to protect the posts you are best soaking the post in creosote it's a type of oil that is used specifically to treat wood for this very reason its also used in tar distillation and is commonly available. You can also soak the wood in general motor oil for a week as it absorbs it well and repels water. The plastic would in fact trap moisture in the wood which in effect would increase the rot. Ideally you want to dig the hold deeper and put gravel under the post to allow water to drain easier and then fill the rest of the hole with concrete

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I'm definitly putting gravel in the bottom first. –  TornadoKnight Apr 27 '12 at 21:49
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Also remember to pack and compact it. because the wiggle room in the bottom is amplified the further towards the top of the post you get. water expands the post and then it contracts in the dry. Water is public enemy number one. –  Ryan Walkowski Apr 27 '12 at 21:52
    
Thanks. Good to know. –  TornadoKnight Apr 27 '12 at 21:56
    
Both Kreosote and Tar are both toxic materials, though. Common, but just something to consider before sticking into the ground. –  DA01 Apr 27 '12 at 22:27
    
A valid point however the toxic variety of creosote was coal tar creosote but it has been superseded with wood creosote which is very much less toxic and you now get a water/gas formulations which are meant to be non toxic. –  Ryan Walkowski Apr 27 '12 at 22:39
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