# Concrete around posts



## dragonjaze

I'm not trying to be snarky; I'm honestly curious about this.

Why is it ok to bury a post in concrete in the ground, but surrounding a wood post with concrete above ground is a no-no? :nono:

I've been doing a lot of researching and reading, and everything I'm reading says not to let a concrete slab touch or surround a wood post.


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## rancher1913

the concrete in the ground anchors the post evenly. the concrete around the post at the top (slab or patio) will cause two problems, 1 it makes a weak spot that will crack or 2 as the cocrete expands and contracts with the weather it could shear the post and cause the structure to fail.


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## Bearfootfarm

> Why is it ok to bury a post in concrete in the ground


It's really not a great idea to use it at all.

People mainly do it because they "heard" it was a good idea


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## gobug

As a licsensed termite person in CO, when I was called for an inspection, I looked at anything attached to the house. Any deck or fencing posts were looked at. If the cement was above ground and sloped away from contact with the wood it was OK. If it was below ground in any way it was a negative. The concrete is great if you elevate the posts which are set into the concrete.
Gary


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## Ross

I dunno we anchored ours underground because thats what the engineered drawings said to do. Seems to be working out OK.


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## littlejoe

Any form of liquid moisture, hitting the post, drains alongside it, becoming trapped between it and the concrete. Thus multiplying the moisture over and above, to one set in soil or gravel.

I'm totally against setting wood in concrete, even sloping away from the post. Pipe is differant! It can be pretty much sealed.


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## Darren

It depends on climate, soil and possibly the water table. Some places you can get away with setting posts in concrete. In other areas, the water it traps next to the post creates a good area for fungus growth. Fungus is what causes wood to rot. When water can drain through the soil and move away from the post, the post will last longer.

In some areas it doesn't matter whether the post is set in concrete or not or heartwood or softwood. The conditions encourage fungal growth and the post rots off at the ground surface sooner than later.

If you're building a structure consider using the marine grade 2.4 CCA treated wood for the posts. Fungus won't touch that stuff for probably 50+ years. 

The other issue to consider is the bearing strength of the soil. In weak soils you want to reduce the loading on the soil. A larger cross sectional area post will do that. Pouring concrete around the post, as long as the concrete is locked onto the post, will do the same.


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## RonM

Pole barn builders now use sono-tubes keeping the conncrete from touching the poles?


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## Ross

We've got 3 buildings that use posts set into concrete under ground. One is over 50 and holding fine (creosoted hydro poles) , one is pushing 25 and we dug out one post to extend it and it was solid as a rock (PT in cement), the third is about 15 years old and it seems to be just fine so far. We're not especially wet or dry here.


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## Darren

Creosote is one of the best wood preservatives. The fence pole test results I saw showed that creosoted posts went over 50 years before deterioration started. Even then the deterioration was minor. Those were posts set in the ground without concrete. The only posts in the test that went past 50 years without any deterioration whatsoever were osage orange.


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## PlicketyCat

We have a high water table and wicked frost heaves, but blessedly no termites. When we set the footings for our cabin posts, we poured concrete pads and piers, and anchored the wooden posts on top of them well above ground level, with a capillary break between them to keep water from wicking up from the concrete into the wood. It also allows us to jack-up the house and replace the concrete if it does get saturated, freezes and cracks (not uncommon), or replace the post if it should start rotting or get infested with carpenter ants (less likely).

For our buried wooden fence posts, we used treated wood and filled in with packed gravel, not concrete. The gravel will drain, the concrete will not.

YMMV based on climate.


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## djberg

I design pole barns and get feedback from hundreds of builders. I also inspect pole barns for an insurance company.

In moist soil or in a wet climate, wood set into concrete, above or below grade seems to rot quickly. The critical area seems to be a few inches above grade to about 18" below grade. Today's pressure-treated wood does not seem to be as good as older chemical treatments were. Today's formulas are less than five years old, so they haven't really been tested. 

You might do best by keeping wood posts out of concrete by using a hot-dipped galvanized post mount or a plastic sleeve post protector.

Don

TodaysPlans.net


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## BradnDC

dragonjaze said:


> I'm not trying to be snarky; I'm honestly curious about this.
> 
> Why is it ok to bury a post in concrete in the ground, but surrounding a wood post with concrete above ground is a no-no? :nono:
> 
> I've been doing a lot of researching and reading, and everything I'm reading says not to let a concrete slab touch or surround a wood post.





dragonjaze said:


> I'm not trying to be snarky; I'm honestly curious about this.
> 
> Why is it ok to bury a post in concrete in the ground, but surrounding a wood post with concrete above ground is a no-no? :nono:
> 
> I've been doing a lot of researching and reading, and everything I'm reading says not to let a concrete slab touch or surround a wood post.


I have this exact problem and mistake I’ve made using 6x6 posts to holdup a medium size deck. I have close to 3/16 inch vertical splits in the posts now, but I have several posts and I do feel like they will hold for the long term. However, I need peace knowing people are not at risk of course. 

I need to know your thoughts....My plan is to install additional 6x6 posts parallel to the ones with splits but they will situate on top of the patio with room for drainage where it meets the surface. The slab is 4 inches but I really don’t feel these new posts will ever get considerable weight. Does this sound like a good strategy. With this approach, at least I’ll know there’s a major problem when the concrete begins to crack instead of the existing posts failing abruptly.


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## BradnDC

rancher1913 said:


> the concrete in the ground anchors the post evenly. the concrete around the post at the top (slab or patio) will cause two problems, 1 it makes a weak spot that will crack or 2 as the cocrete expands and contracts with the weather it could shear the post and cause the structure to fail.


I have this exact problem and mistake I’ve made using 6x6 posts to holdup a medium size deck. I have close to 3/16 inch vertical splits in the posts now, but I have several posts and I do feel like they will hold for the long term. However, I need peace knowing people are not at risk of course. 

I need to know your thoughts....My plan is to install additional 6x6 posts parallel to the ones with splits but they will situate on top of the patio with room for drainage where it meets the surface. The slab is 4 inches but I really don’t feel these new posts will ever get considerable weight. Does this sound like a good strategy. With this approach, at least I’ll know there’s a major problem when the concrete begins to crack instead of the existing posts failing abruptly.


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## melli

BradnDC said:


> View attachment 66405
> View attachment 66406
> 
> I have this exact problem and mistake I’ve made using 6x6 posts to holdup a medium size deck. I have close to 3/16 inch vertical splits in the posts now, but I have several posts and I do feel like they will hold for the long term. However, I need peace knowing people are not at risk of course.
> 
> I need to know your thoughts....My plan is to install additional 6x6 posts parallel to the ones with splits but they will situate on top of the patio with room for drainage where it meets the surface. The slab is 4 inches but I really don’t feel these new posts will ever get considerable weight. Does this sound like a good strategy. With this approach, at least I’ll know there’s a major problem when the concrete begins to crack instead of the existing posts failing abruptly.


That looks pretty typical of posts. Over time, they dry out and split (not all the way through). Usually happens when using the 'heart' of a tree. No big deal. 
There should be span tables for your area...it looks ok, but it never hurts to check local codes. 
Deck failure that I've dealt with is poor ledger connections and poor footing, post and beam selection (especially on slopes). I suspect your posts, beams and joists are all fine. I would prefer to see triple ply on beam. Double ply, as you have, is where I've seen 'beam crippling'. But, I doubt it in your case, given the post wraps the beam.


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## fordy

BradnDC said:


> View attachment 66405
> View attachment 66406
> 
> I have this exact problem and mistake I’ve made using 6x6 posts to holdup a medium size deck. I have close to 3/16 inch vertical splits in the posts now, but I have several posts and I do feel like they will hold for the long term. However, I need peace knowing people are not at risk of course.
> 
> I need to know your thoughts....My plan is to install additional 6x6 posts parallel to the ones with splits but they will situate on top of the patio with room for drainage where it meets the surface. The slab is 4 inches but I really don’t feel these new posts will ever get considerable weight. Does this sound like a good strategy. With this approach, at least I’ll know there’s a major problem when the concrete begins to crack instead of the existing posts failing abruptly.


...............................................
.........With those cracks as large as they are , You can squirt a large quantity of water proof glue into the cracks and then use long lag bolts to pull both pieces together ! I'd start injecting glue at the TOP of the crack and let gravity perform it's magic . , fordy


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## Designlover

rancher1913 said:


> the concrete in the ground anchors the post evenly. the concrete around the post at the top (slab or patio) will cause two problems, 1 it makes a weak spot that will crack or 2 as the cocrete expands and contracts with the weather it could shear the post and cause the structure to fail.


Yes, I agree. It's not smart to use concrete since it can cause you some severe damage and forces you to do more work in the long run.


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## weaselfire

RonM said:


> Pole barn builders now use sono-tubes keeping the conncrete from touching the poles?


Nope. Sonotubes are quick forms for pouring concrete.

Jeff


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## Esteban29304

Many people do not realize that there are different grades of pressure treated lumber. Using lumber with a lower " retention grade" , [ less preservatives ] , especially in contact with soil, will lead to quicker rot & termite damage . I have seen 4 x 4, & 6 x 6 posts destroyed by termites in less than 5 years, due to the posts being lower grade & buried. I like to use the best grade for everything. Check the labels at the end of the boards. 

https://www.proremodeler.com/new-rules-pressure-treated-lumber


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## melli

Esteban29304 said:


> Many people do not realize that there are different grades of pressure treated lumber. Using lumber with a lower " retention grade" , [ less preservatives ] , especially in contact with soil, will lead to quicker rot & termite damage . I have seen 4 x 4, & 6 x 6 posts destroyed by termites in less than 5 years, due to the posts being lower grade & buried. I like to use the best grade for everything. Check the labels at the end of the boards.
> 
> https://www.proremodeler.com/new-rules-pressure-treated-lumber


Interesting link...the use of CCA (Chromated Copper Arsenate - old school wood preservative) was banned almost two decades ago around here (except in certain industries). Obviously, chromium and arsenic were bad for environment, and to humans (how many folks wear a mask and gloves when handling pressure treated wood?). So, they came up with a 'gentler' formulation called ACQ (Alkaline Copper Quaternary - Copper with a fungicide and bactericide inhibitor). Having worked with stuff (ACQ) since adoption, it has a habit of eating metal...I've seen aluminum flashing dissolve, and improper fasteners. I use SS wherever possible and/or ACQ rated fasteners/hardware. 
Recently, I've seen several decks in my old hood (12 yr old decks) have rot issues. Two have been rebuilt. Seems ACQ wood, in above ground applications, isn't the panacea it was supposed to be. We avoid ground contact with any wood for structures around here. Our rainforest climate eats wood. 
I have to build a deck for my home, which does cause me some concern, in light of the evidence piling in. One thing we are doing to mitigate premature rot, is putting blueskin or poly over tops of beams and anything that is 2-ply. It limits water egress, and keeps tree junk/dirt from pooling on top of beams. And definitely avoid using non-pressure treated wood, even for fascia or decoration, on decks. We have found the non pressure treated wood can infect the pressure treated wood. 

Here is an example:
First pic, the OEM beam. It 'looks' like a simple replacement will do. Once removed (note the debris - the beam crumbled), it was discovered it had infected the joists (2nd pic), which resulted in a deck teardown and rebuild. 

























Deck was barely 11 yrs old... 
The joists were actually in good shape, except where in contact with beam. Even the deck boards were ok. Rot was also found around rim joist. It was so bad, the lattice skirting was holding up railing.


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## Esteban29304

WOW ! Major damage.
I live in Florida & you can count on water, or termites to go after the wood. Many here use Cypress, when not in touch with the ground. Most new pressure treated lumber that is found at local lumber yards has a lower retention rate , & just will not last . I added on to a deck that was about 15 years old. I let the new P.T. wood dry, applied primer, & good quality paint. It lasted 5 years before rot damage forced me to replace it, & that includes rotting wood that did not contact the ground ! . The old deck is still solid & 20 years old.


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## MichaelZ

Keep the wood dry and not sitting in water. Otherwise it will rot, treated or not. Sooner or later.


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## Sebastian C

Make concrete pilings above ground level. and put a post anchor on top, or even just a 1/2 rebar pin sticking out the top. Bolt the post to the anchor or drill a hole in the bottom and set it on the pin. They build houses in earthquake zones with the pin method. Termites and other critters are fatal here in the tropics, I've been conditioned to never think it's okay to set posts directly in concrete


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## zuren

RonM said:


> Pole barn builders now use sono-tubes keeping the conncrete from touching the poles?


My dad just had a large lean-to attached to the back side of his pole barn. The builders sank SonoTubes, filled with concrete, and set a bracket on top. The posts supporting the roof mount into the brackets and never touch the dirt.


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## Darren

melli said:


> Interesting link...the use of CCA (Chromated Copper Arsenate - old school wood preservative) was banned almost two decades ago around here (except in certain industries). Obviously, chromium and arsenic were bad for environment, and to humans (how many folks wear a mask and gloves when handling pressure treated wood?). So, they came up with a 'gentler' formulation called ACQ (Alkaline Copper Quaternary - Copper with a fungicide and bactericide inhibitor). Having worked with stuff (ACQ) since adoption, it has a habit of eating metal...I've seen aluminum flashing dissolve, and improper fasteners. I use SS wherever possible and/or ACQ rated fasteners/hardware.
> Recently, I've seen several decks in my old hood (12 yr old decks) have rot issues. Two have been rebuilt. Seems ACQ wood, in above ground applications, isn't the panacea it was supposed to be. We avoid ground contact with any wood for structures around here. Our rainforest climate eats wood.
> I have to build a deck for my home, which does cause me some concern, in light of the evidence piling in. One thing we are doing to mitigate premature rot, is putting blueskin or poly over tops of beams and anything that is 2-ply. It limits water egress, and keeps tree junk/dirt from pooling on top of beams. And definitely avoid using non-pressure treated wood, even for fascia or decoration, on decks. We have found the non pressure treated wood can infect the pressure treated wood.
> 
> Here is an example:
> First pic, the OEM beam. It 'looks' like a simple replacement will do. Once removed (note the debris - the beam crumbled), it was discovered it had infected the joists (2nd pic), which resulted in a deck teardown and rebuild.
> 
> View attachment 67944
> 
> View attachment 67946
> View attachment 67946
> 
> 
> Deck was barely 11 yrs old...
> The joists were actually in good shape, except where in contact with beam. Even the deck boards were ok. Rot was also found around rim joist. It was so bad, the lattice skirting was holding up railing.


CCA is still available. Even the 2.4 lb/cuft marine grade is available. You just have to know where to buy it.


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## weaselfire

That deck is near identical to the one I'm also rebuilding. If you find the Marine trade posts, they will never rot. At least not in my lifetime.

Concrete piers have their own issues too, and in many areas, floating decks on pier blocks can be the answer. Build for codes in your area, and find your answers in places other than the big box home stores.

Jeff


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