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Old 09-15-2012, 07:45 PM   #1
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Nervous about Concrete in Post Holes


We have a big deer problem on Vancouver Island so I've been building a deer fence around my 20 x 20' veggie garden. I used 10' pencil posts and set them in 34" holes which I packed with gravel shavings (1/4" gravel and smaller) because I wasn't sure I wanted this to be a permanent arrangement. However it's recommended to set my 4x4 x 10' cedar posts in concrete. I had to hand dig 3' holes because of all the rock and clay--at about 1.5' it's hard clay which was no fun at all getting out. Two questions: 1. Because my holes are hand dug it's hard to have them wider on the bottom than the top as recommended. The best I can do is straight down and wider at the top. Is this really going to compromise post stability? I have some sonotube. I could use to make the top 8" area a little less wide then I could pack soil back in around the outside of that. 2. I'm getting nervous about this concrete idea. Is it really necessary to use concrete for my gate posts? There isn't much issue with wind force as the posts will just be holding up black plastic deer screen.

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Old 09-15-2012, 08:53 PM   #2
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Nervous about Concrete in Post Holes


You're much better off not using the tubes and having the concrete in direct contact with the undisturbed soil. It will provide much more support than any fill you put in. Not having the holes wider at the bottom shouldn't be a major issue. Make sure the bottom of the posts are not covered with concrete so water doesn't become trapped in them.

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Old 09-15-2012, 08:59 PM   #3
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You are making this way to complicated. Posts do not need to be bigger on the bottom than the top. How much uplift do you think your fence is going to experiance? Make your post holes 24" deep about 12" in diameter. Place the concrete in the hole and walk away. Make sure that the post is positioned in a plumb manor before the concrete starts to set up.

I would recomend that you concrete the gate posts.
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Old 09-15-2012, 11:21 PM   #4
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Nervous about Concrete in Post Holes


Thanks Msradell, I get it about not using the tubes. Fencers told me about making the holes bigger on the bottom and I found that recommendation by several posters [no pun intended] on line. I managed today to get out a couple of inches wider on the bottom. Not easy at 3'. Good info about not using tubes. I noticed that one of my post holes had 8 inches of water on the bottom today. I that will be the case with all of them soon due to rain and clay. I was planning to put in about 5" of gravel on the bottom so, as you suggest, I will leave some of the post in the gravel level before adding concrete.
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Old 09-15-2012, 11:25 PM   #5
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You are making this way to complicated. Posts do not need to be bigger on the bottom than the top. How much uplift do you think your fence is going to experiance? Make your post holes 24" deep about 12" in diameter. Place the concrete in the hole and walk away. Make sure that the post is positioned in a plumb manor before the concrete starts to set up.

I would recomend that you concrete the gate posts.
Thanks Rocket. My posts are 7 feet above ground so I had to go deeper especially since our soil gets very soggy during the rainy season--which is a long season here. There is not going to be much uplift as the climate is mild here.
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Old 09-15-2012, 11:33 PM   #6
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I don't understand why you want to leave any of the post embedded in concrete as they'll eventually rot, unless I'm misunderstanding something. I'd use these, and mount the post properly.
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Old 09-16-2012, 01:02 AM   #7
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I know I'll catch heck for this ..... but here goes

posts typically rot when embedded in concrete at the point where the post comes out of the concrete because concrete will shrink when it hardens and a depression may form on the top to trap water (exposed to oxygen in the air). put a slope on top of the concrete so that water runs off. Another issue is using above ground pressure treated wood (or non-treated, or non-weather resistant wood) inserted into the ground, when it should be rated for ground contact. Difference is the amount of chemical used and retained in the wood, ground contact needs more preservative to last. For wood embedded in the ground to last longer it needs inspection and maintenance.

From http://www.restorelogs.com/why_do_logs_rot.htm (you can do your own google to verify)



The rot organism needs four ingredients to begin degrading wood. It needs:
  1. Temperatures between 60 and 90. This is why most of the active rotting occurs during our hot, humid Midwestern summers.
  2. Oxygen - rot needs it to get going. This is why wood that is underwater does not rot. There is not enough ‘free oxygen’ for the process to take place.
  3. A food source. This is what the rot organism eats - in this case wood- aka -Your house.
  4. Moisture content between 20% - 30% in the wood’s fiber. While this percentage varies from species to species, most wood will start to deteriorate at around 20% moisture.
Wood sitting in water is less lightly to rot than wood exposed to 20%-30% moisture in the wood. All you have to do is look at all the piers and wharfs that were built a hundred years ago and still standng.

Lastly, wood columns properly embedded in the ground will have greater lateral resistance than wood columns attached above ground with a metal bracket. I'm talking just columns without any walls or bracing, as in the case of fence posts or utility poles. One of the principals of post-frame construction.
Just my thoughts ....
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Last edited by GBrackins; 09-16-2012 at 06:41 PM.
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Old 09-16-2012, 12:59 PM   #8
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I will definitely put a slope on the top of my concrete. Just have to resolve how to keep the concrete at the top from sprawling out into my unfinished landscaping. May have to build a small form. And yes I have ruled out metal saddles since these posts are for a gate. My posts are cedar but I also applied Lifetime Wood Preservative a non-toxic wood preserver. I'm feeling more confident now. Thanks for helping me.
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Old 09-16-2012, 05:26 PM   #9
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Glad we were able to help! You can actually leave the top of the concrete a little below grade if you want to as long as its slopes away from the post.
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Old 09-16-2012, 11:43 PM   #10
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Glad we were able to help! You can actually leave the top of the concrete a little below grade if you want to as long as its slopes away from the post.
Oh I wish I had seen this earlier. I thought I had better have the concrete above grade so I build some forms for the post base. Could be a bit of a toe jammer, but I'll be doing some paths around the posts and can build up the grade. Building the forms and leveling the posts took longer than doing the concrete work but it all went well. Glad I didn't have the fast set concrete. Now I'm inspired to do more concrete work. Thanks again.
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Old 09-17-2012, 01:49 AM   #11
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Nervous about Concrete in Post Holes


I have installed hundreds of posts, and I don't use any concrete at all ever, just gravel for the bottom, and the same dirt taken from the hole you are digging. If there is ever any problem (I have never had any so far) it is easy to extract it and set it back.
The problem with concrete that I see, they can still move (then is so hard to fix), and no matter what you do, water is going to get between the concrete and the wood, and the post is going to rot eventually there, even if you slope the top of it. If using dirt, the water goes straight down and don't stay close to the post. Airdrie, Alberta.

Last edited by Pirulo; 09-17-2012 at 01:51 AM.
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Old 09-17-2012, 09:17 AM   #12
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I don't know where you are located. Deer suggests it is wooded to me. One problem with wood in contact with soil is termites or other wood destroying organisms. As an exterminator I did termite inspections. One of the things I specifically looked for was ground contact with untreated wood in contact with the structure. That included decks, porches, and fences. It was acceptable to have the cement above ground level and sloped away from the wooden post.

I am working on building a mtn cabin and have very hard soil and frequent deer visitors. I have seen live termites 5 times. This is in an arid mtn climate. I also love to garden.

My thought is to make the fence portable to simplify installation. Maybe panels connected together making a W. Since chain link comes in different lengths and heights, and 1 1/4" fence rail is 20ft the size of the W is flexible and it could be moved or repaired easily.

Deer do not like _-_ entries. The - would be larger so it would be like a hallway. No gate.

good luck
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Old 09-17-2012, 09:46 AM   #13
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Do you have termites in Vancouver? There are none where I live (close to Calgary), it's too cold in winter for them to survive. We don't have rats neither (but I wouldn't be surprised that with the climate getting warm, we will have them soon). Then I agree, you'll need the concrete, and pressure treated posts (or they will rot being in contact with the dirt). How high should the fence be so deers don't jump over it?
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Old 09-17-2012, 10:03 AM   #14
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There are more than 50 different kinds of termites in North America. Those of greatest risk to structures are what most people refer to as "termites". The southern areas have a lot more risk of extensive termite damage. In CO there are only a few of the higher risk types of termites. Altitude and cold winter temperatures may influence which types survive, but they are still there. I suspect the same is true near Calgary and other areas there. There are definitely termites in Alaska.

I think 7ft is too high for the deer. 6ft might work too.
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Old 09-17-2012, 11:52 AM   #15
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During out basement reno there was no sign of termites and haven't heard of if being a problem here in Victoria....however we have a huge problem with deer right in the city of Victoria. There is a big debate going on concerning what to do about it. There are very few plants that deer don't like. They've eaten my oak trees, tulips, blueberry bushes, even the blackberries--see pic--but they covet my veggie garden the most. I have a 3' fence in my front yard and they just step right over it. I bought a fence product that is specific for deer and it is 7 feet high. The posts I bought which are also for deer fencing are 10' (put 3' in the ground). I was hoping my deer fence around my vegetable garden was going to be temporary--hence not wanting to put in 3' of concrete near where I'm planning a driveway reno, but the local sentiment is to keep the deer. I ended up using concrete only for my gate and set my pencil posts in gravel shavings.
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