Concrete Post Rot Myth BUSTED - Does Concrete Rot Fence Posts?

When you fill in your post hole with concrete, it traps in moisture and makes the fence post rot, right? WRONG! Does concrete really rot fence posts? Today I'm busting the concrete fence post rot myth and explaining how this is false. Check it out and let me know what you think!

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[elle_luvs_tblw]

I did fencing for ten years and replaced many rotten posts. When I dig up the posts, the part surrounded in concrete is still solid. It's the part that is exposed to soil an inch or two below the surface that rots.

[allcountyfenceryan]

I am a fence contractor in Florida, with over 2 decades of experience. We've removed hundreds if not thousands of wood fences. From first hand experience, I can tell you that it that wood posts that have no concrete versus with concrete, rot at the same rate. I can also tell you that the posts with concrete are much harder to remove from the ground then those without. I've had many more customers complain that the previous contractor did not use concrete, and as a result of a hurricane or storm, it caused the fence to lean or fall down. Because of the mostly sandy conditions in my area of Florida, I recommend concrete on wood. I can also tell you that most posts rot at the surface, where there is no concrete. Conditions are the biggest factor as to what causes posts to rot. If you have a lot of standing water in your yard, you can bet that it will rot quicker. If you don't maintain your yard i.e. clearing leaves, mulch, grass etc., it will rot quicker because of the moisture yard waste holds against the wood. If you have a particularly wet yard, and/or you don't want to be bothered by maintaining wood or having to replace it every 10-15 years. I would highly suggest a PVC/Vinyl fence instead. Yes, it is true there are some products out there that you can use to cover the wood posts to prolong wood rot, or metal posts instead, however the costs of these products usually ending up costing the same or more than a PVC/Vinyl fence. That's why I would highly recommend PVC/Vinyl instead of wood. Also, keep in mind that in 2003 the EPA banned CCA in lumber treatment, . The treatments they use today are not as good, and as a result wood fence do not last nearly as long as they used to. Fences installed prior to the ban could last 20-30 years, versus now, which is about half of that. That is likely where most of the confusion is coming from. I think most consumers are upset that wood is not lasting as long, for good reason. But the chemicals used for pressure treating lumber are the biggest factor for wood fencing rotting at a much faster pace. Just think about all products that have been produced in the past 20 years. Do they last as long as they used too? In most cases no. And in my opinion, most industries do this with purpose. So, you by their product again sooner, rather than later.

[brianboyle]

My experience. I built a 40' long bridge over the creek behind my house 20 years ago. I water jetted the posts into the creek bed and did not put any concrete around the posts. The bridge is still there and posts are all firm. That same year I installed 400 feet of cypress fencing closer to the house with and put concrete around half of the posts. Several of the fence posts have already failed and in each case the ones that failed had concrete around them. In each case, the post was rotted off just above the concrete and just below the concrete. I live in South Florida and the ground is wet the entire year. Personally, I will not be putting concrete around any future fence post installations, as they seem to last longer without it. I also have to question the quality of the pressure treated lumber these days compared to the pressure treated lumber 20-30-40 years ago.

[iananderson]

One of the most interesting topics…. Love to hear the differentiating opinions. Truth be to about what I know in that most posts “break or rot” right at or above grade. In the many hours of research I’ve done I have found the best method it to set the post in concrete and use a trowel to make the concrete slope away from the post, and then don’t back fill it with dirt! Even though this won’t entirely prevent the rot from occurring it will definitely slow the process. Also, one thing to note is that WOOD WILL MOVE. Even if you set it in concrete, the post is more than likely wet when you place it and therefore when the post begins to contract (due to moisture loss) then a small gap develops between the post and the concrete which will also invite water to hang out next to the post. I do think that it is funny how many fence guys use gravel in the bottom of the hole… to help the water drain out of the bottom of the post…. Thai is a very funny concept to me as in the area I live we have lots of clay and rain. There is no way any amount of gravel would keep the post dry.

Also, I recently dig up a few posts that weren’t rotten at all, but the previous fence contractor set the concrete about 10” below grade and tree roots had actually grown through the post and broken it off. Thus another reason that the concrete should go all the way to the top of the soil or grass line.

[naterbator]

It's when rain water or watering the area around the fence, when the ground is above the concrete that water travels down the post into the hole. The post is being kept moist from the retention caused by the dirt. The same concept of why you mulch around trees. Just took out three post set in concrete. The one that had concrete above the ground came out in one piece. The two others below ground level were rotted and broke off and what was in the concrete was completely soggy.

[bigal]

I removed some posts that had been set in concreted holes for forty years. Still solid. When I set posts in concrete I trowel the concrete to stick above the ground and slope away from the post toward the outer edge.

[larryseibold]

There are a ton of theories, many that make some sense to me, but what is missing is a good ASME publication on the subject of wood post setting in soil best practices. It would cover different soil conditions (clay, sand, frost, dry & wet). Thoughts: Is the concrete used hydraulic (not porous to water), or porous? Is the soil wet 300 days a year or dry? My gut tells me that if the soil is basically dry 300 days a year, having a mini French drain at the bottom and around the edge of the porous concrete would be best, or even using only 3/4 crush base rock to allow it to dry right after any rain etc. In all cases the burred post up to 6" above grade needs to have treatment (0.40 lb/cf or better) or it will rot and get eaten. In my area, we have heavy clay with some loam, and get about 40 days of rain per year, mostly in three months. I think it would be good to have the post be basically dry 85% of the time, and the ASME guys are the one to guide us on how to achieve that.

[moconnor]

That is my experience too. There is no need to set a wooden post in concrete. Water will almost immediatly get trapped between the wood and the concrete and the post will never dry. It will rot after a few years. I've seen this time and time again after 37 years in the construction business.

[mistere]

I dont know if I buy this one. Concrete is porous and also has moisture of its own. I've also removed many posts sealed with conrecete that had rotted bases and perfectly fine tops.

[bigp]

I’ve pulled out many wood posts. I’m my experience, the rot is always near the surface. Never in the concrete.

[johnnynewburgh]

Ever notice a tree stump covered in soil wil rot but when it's not covered it will not rot so when it's covered it has right conditions for microbes. So I believe concrete pier with anchor bracket is the way to go along with side load bracing ?The only way it can rot is if water penetrats wood

[WhiskeyPapa]

0:40 Will the post still _"act like a candle"_ if the top portion of the post is stained and sealed (such as the Expert Stain and Seal) with regular reapplication maintenance?

I am looking at building a fence, and am looking at the "char and tar" method for the part going in the ground, with a nice mahogany stain and sealant on the post. I'm curious if I'm destroying any breathability in the wood with that method, though, and thus promoting rot/decay.

[jamiebennett]

you got this right, I've had to dig up too many posts and concrete due to rotted posts at the surface, those completely surrounded by concrete were still intact those with gravel were gone at the bottom and rotten on the way up

[richardr]

Going through this right now. The 2 main reasons I have several posts that rotted- 1) the idiots that installed some of them put the post, then the concrete, instead of putting in a little concrete at the bottom 1st, then the post, and then the rest of the concrete-meaning the bottom of the post was bare, sticking out of the bottom of the concrete and soaking up all the moisture. 2) The most widespread damage, because it not only involves the 4x4 posts, but also the bottom of all the fence boards- the entire fence has sunken about 3-4 inches (gotta love south Florida sand). The bottom of the fence is now embedded into the ground and the affected posts have 4-5 or more inches of dirt sitting on top of the concrete. What a nightmare. To be fair, it took years to happen. One day, I looked out back and thought I was going crazy because I could have sworn I never used to see the backdoor neighbor's heads, or see through the top of the glass on their French doors. Now I know I wasn't imagining it. Lesson learned- I hired a "contractor" and later learned, he turned around and hired 3 homeless alcoholic bar buddies to actually do the job.

[ATVERKING]

Would it be a bad idea to add dry concrete mix to the bottom, add the post and then surround it in concrete. Essentially encapsulating the post from the ground down in concrete?

[noelcannon]

I recently saw an advertisement for a post wrap that actually glued to the post at the ground line. They have a 20 year warranty if you use their product and they showed how the product works and it seem to have some merit. Have you heard of any of this?

[jaywesselink]

Joe, I am in Minneapolis and frost line is about 48 inches. The best I can get with my auger and cleaning out by manual auger is 44 inches.

[jamie.]

Agreed 👍 🤝. Did this on deck 4 x 4 posts. And still working

[radurobert]

I'm thinking to burry the wood post without concrete by fallowing4 steps . 1 - burining fallowed by 2 - 30% linseed oil combined with 70% mineral spirits 3 just linseed oil 4 a bitumen final layer

What if you place the sono tube section 4 inches above grade and pour to this height.
Seems to make sense to me since the post always rir at ground level 😊