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Old 11-05-2012, 04:48 PM   #16
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Pressure treated posts set in concrete?


In Chapter 23 of the IBC (International Building Code) specifies the use of preservative-treated wood when in contact with concrete.

I've been searching for any authoritative study which would back up the tales of concrete causing preservative-treated wood to decay.

Anyone who has testing results which would lend credence to the apparent old-wive's tale of concrete decaying preservative-treated wood, please share them with me.

Your assistance is appreciated.

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Old 11-05-2012, 07:05 PM   #17
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Pressure treated posts set in concrete?


I have inspected some 20 odd houses damaged by hurricane flooding that were supported on wooden piles. Some of the piles were directly embedded in sand, some were embedded in concrete, and some were driven into the ground and packed around with gravel or crushed stone.

The only thing the houses had in common was that the house above the piles had sustained massive damage from flooding. In a few cases, part or most of the foundation had been washed away as well, although in most cases the foundation was intact, while the house was mostly destroyed. I would post pictures, which are really pretty interesting, however it would violate my contractual agreement with the companies I worked for, so unfortunately I cannot.

I can say that the wooden piles exposed to salt water were damaged primarily in the tidal zone, and the majority of damage was from marine insects. The dry zone above the high water line was generally in excellent condition, even for untreated timber piles that were 50 or more years old. In many cases, portions of the piles well below the normal sand line were exposed due to loss of shoreline, and the originally buried portions of the piles were in generally good condition. The portion of the pile subject to wetting and drying was always the worst, and in many cases there was 50 percent loss of section. In a few cases, I wondered how the house even stood.

Based on my inspections, and literature I have reviewed, I have come to the belief that treated or untreated wood performs very well if it is kept either completely dry, or is constantly saturated, either with fresh or salt water. I have inspected numerous dams built on untreated wooden piles that are over a hundred years old, and in several cases we cored the wood, and the conclusion is the same. If the wood is always wet or always dry, it performs very well. If it is subject to alternate wetting and drying, it rots relatively quickly.

I have heard all sorts of stories purporting to have evidence that embedding wood in concrete causes the wood to rot quickly. I have never personally seen any evidence of this, and like PoleBarnGuru, I would very much like to see a well developed report on this topic. I believe that the portion of the pile just above the ground is likely to be the most at risk for rot, hence must be the best protected, whether by use of waterproofing agents, or perhaps wrapping in fiberglass or similar material.

Several houses I inspected which had severe foundation damage were being rebuilt, using precast, prestressed concrete piles, which can be driven directly into the ground, and provide outstanding resistance to rot. A few houses were being rebuilt using steel piles, which also can be directly driven, and will last a very long time under normal service conditions. There is still a thriving wood pile industry, as wood is less expensive than either concrete or steel, and not every building needs to last a hundred years or more.
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Old 08-09-2013, 09:32 AM   #18
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Pressure treated posts set in concrete?


Lifetime...or close guarantee for imbedded posts.

I wrap the post in 25# roofing felt. I cut a piece to fit the bottom and staple it solidly closed, then I wrap over that all the way up the post for the length the post will be buried - Stapling completely, then heat the seams with a torch. (Basically wrap it like a present! )

I set the post and pour the concrete topping it off in a decorative slope to make all water run-off and away form the wood.

I have never been able to test my applications past 18 years to-date but at this writing they are like I did them yesterday!

I do keep a coat of oil based paint on the areas I can reach, re-painting as required. (18 years and only the second coat of paint)
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Old 08-12-2013, 09:42 PM   #19
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Pressure treated posts set in concrete?


quick side bar question here instead of making an entire new thread. Im sinking one 4x6 PT post tomorrow that will be part of a 7' (tall) fence and will be using concrete... Does the 1/3 rule apply to 4x6s as well or should I go down a bit further? I was told to be safe and just sink it 4'... any input?

Thanks ahead of time

EDIT*** Also, one end of the fence will be butting up against my brick home. Do I want it to butt right up against or leave a.... lets say 4"-6" clearance away from the building?

Last edited by mjvdet13; 08-12-2013 at 09:46 PM.
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Old 08-13-2013, 05:39 AM   #20
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Pressure treated posts set in concrete?


Quote:
Originally Posted by mjvdet13 View Post
quick side bar question here instead of making an entire new thread. Im sinking one 4x6 PT post tomorrow that will be part of a 7' (tall) fence and will be using concrete... Does the 1/3 rule apply to 4x6s as well or should I go down a bit further? I was told to be safe and just sink it 4'... any input?

Thanks ahead of time

EDIT*** Also, one end of the fence will be butting up against my brick home. Do I want it to butt right up against or leave a.... lets say 4"-6" clearance away from the building?
I would sink it below the frost line and be done with it. With that said Mr. Overkill here would use an 80# bag of concrete per hole also....

If you buy 10' 4 X 6 and your frost line is less than 3' you are good to go, otherwise you need to go to 12' lumber and that also adds a lot to your overall cost.

Butting the house or not: Butt the house, which also keeps out (or in) creatures. Butting the house also allows you to attach to the house creating a strength member. (Bolting a 4 X 6 to the house!)

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