Treating cedar fence posts to prevent rot

janedibberOctober 12, 2007

We happen to come across 6 sections of cedar picket fence with 6x6 cedar posts for a reasonable price (free). I understand cedar is not as rot resistant as PT, but is there something we should do to the posts which will be in contact with the ground. One web site noted soaking the bottom sections in creosote. Are there other recommendations? Thanks!!

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Most of the really good old preservatives are no longer available (like creosote)where I live (CA.).

I have had some success soaking redwood posts in copper-green. I doubt if painting anything on would do too much good.


    Bookmark   October 12, 2007 at 12:54PM
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copper green? never heard of it, but will look into it. thanks.

    Bookmark   October 12, 2007 at 1:14PM
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Of course it's the water that makes them rot. So after you get the posts in the holes, don't backfill the holes with dirt or concrete. Both of those will hold moisture.

Try filling the holes with "Quarry Processed" (QP) gravel. It's maybe 1/2" stone and less, mixed with some lime. Once the lime sets up, it's gets pretty solid, but it still drains water.

    Bookmark   October 15, 2007 at 6:02AM
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It takes about 25 years for a cedar 6x6 to rot out. The rest of that cedar fence will gone by then.


    Bookmark   October 15, 2007 at 11:27AM
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Al, redwood used to be like that. No more. A 4x4 all heart redwood fence post used to last 25 years, now they last about 5. I'm not sure if cedar has suffered the same decline in quality.


    Bookmark   October 15, 2007 at 8:42PM
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I am in the middle of putting in a cedar/ipe fence (cedar posts, ipe panels). It has been a 18 month "weekend" project, and I did a lot of research on the post setting end of things.

I am using 5x5 northern white cedar for the posts. After reading much advice, I decided to set mine about 36" down, using alternating layers of tamped soil and gravel. Putting cedar posts in concrete is not adviseable for a variety of reasons (from what I understand anyhow).

If you can get creosote, a lot of people do recommend that. I talked to a guy who has a long history of building fences, and short of creosote, he recommended "waxing" the cut end that is the ground. He said besides water/moisture settling around the whole buried post, the capillary action of the wood draws massive amounts of moisture deep into the wood. A heavy layer of wax on the end will help deter that action quite a bit.

Someone else reconmended something called "termin brown" I believe, a preservative that you can buy at your local chains. I myself didn't try it.

When setting the posts, be careful if you have clay. Sometimes the gravel layers just give the water a place to run to, collect around the post, and then sit on top of the clay.

As far as cedar quality...I hear that the quality isn't like what it use to be. Back where I grew up, there are cedar posts in fields that have been in the ground 30+ years holding up fencing. But I guess the cedar coming out of the mills now has gone to crap like the rest of the lumber out there. If the posts are good solid heart wood, then you should be good to go for quite a while. If their is a lot of sap wood, could be a problem. I have heard that Red Cedar in particular right now does not have a good life span at all.

I am just a diy'er, so don't take anything on my word at all. I am hoping to get 12-14 years out of my posts, but I am a bit concerned about whether I made a bad judgement call to use cedar or not.

    Bookmark   October 15, 2007 at 11:38PM
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I believe any wood set into the ground will succumb to moisture. I used to set posts with pea gravel for backfill and they lasted a long time. Now I sink concrete below the frost line and attach a stand-off post base for the post. Personally, I believe this is the best solution and if ever one needs to be replaced, relatively easy to do.

    Bookmark   October 16, 2007 at 8:11AM
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There are post jackets out there, or even bituthane all around the post would probably be a good solution.

    Bookmark   October 16, 2007 at 7:09PM
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I need to put a 20 foot post over a clff into a swamp....
I will be putting the small end in the ground and the larger end up to suport the fence. I have cut the tree off my land, but have not dried it or treated it with anything.
If I get lucky the post will be about 2 foot into the swamp and the cliff will do the supporting.
My question is: SHOULD I drie the post first or will it work O.K. GREEN? If I have to drie it ... HOW LONG?
(It is a good 12 to 14 inches at the bottom/Trunk end)

    Bookmark   March 26, 2009 at 11:44AM
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Go stand in the swamp and consider your plan from that perspective.

    Bookmark   March 27, 2009 at 11:51AM
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Use some of that black jack tar paint on any posts going into the ground, it makes them last a lot longer

    Bookmark   March 13, 2011 at 9:22PM
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The reason why redwood posts just as cedar posts dont last 25+ yrs anymore is because they are comming from tree farms that is generally 10 yr growth. So the wood is nowere near as dence as wen it was being milld from hundred yr.old trees. I would recomenf pressure treated posts they have about a 20 yr rating. I have been installing various styles of fences for a numbber of year.

    Bookmark   September 12, 2011 at 2:16AM
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Actually the question is age old. As a fence contractor for over thirty years We daily run into this question from homeowners. " We just replaced the fence a few years ago and the fence boards are perfect, can't we just replace the posts and re-use the fence boards and rails?" No because when you take the fence apart the boards split and crack. Yes if you spent many hours you can but the time outweighs the cost of just building a new fence.

Now for years and years I have been seeing the same answers on dozens of forums that are totally incorrect and it baffles me. The same answers just reworded from writers that do not do good research.

Post Rot can not occur underground. Protecting the post at the base is what needs to be done. Two of the four elements which rot needs to live- proliferate and exist can not physically happen underground. One is oxygen and the other is fuel- microbes and fungus.

Rot starts at the base of the post where soil comes in contact with the wood. Moisture and fuel rot the wood at that place where the post exit the earth, as a homeowner think and you will see where the posts break and snap... Now we pull posts out daily and the bottom of the posts still often have the tags on them from the lumber yards.

Yes one thing is accurate. The concrete needs to be crowned (sloped) away from the post so water and soil do not touch the posts. But there is also a problem there. In time with wind and mostly because a contractor or homeowner doesnt seal the concrete properly, water will seep in the tiny gap between the post and concrete and sit in there like a pool. In the long run doing more damage- constant moisture and oxygen and fuel. So the posts rot even faster. The base of the post need to be protected. There is a new product on the market called The Post Collar that solves that problem. Or be certain when you crown the concrete that you actually float the concrete away and form a tight seal. There is only one product on the market that does this, The Post Collar. We are using them on all our fences now.
I am not taking the time to do this to advertise my company. Just taking the time on a Sunday morning to try and reeducate people and writers and to answer this age old question asked and respond to in this article.

Troy Emmett

Here is a link that might be useful: University study

    Bookmark   October 19, 2014 at 12:40PM
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I always thought termites destroyed the fence posts and my termite man said no. He said the cement destroys the post over time. He said when you put up a fence put the post in a plastic bag so the wood has no contact with the cement. A concrete man told me that the cement eats his shoes and he has to replace them about every 3 months, so it made sense to me.

    Bookmark   October 19, 2014 at 5:00PM
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