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-   -   Grape Arbor Posts: bury, attach to concrete, or encase in concrete (http://www.diychatroom.com/f19/grape-arbor-posts-bury-attach-concrete-encase-concrete-131070/)

shadetree 01-23-2012 03:32 AM

Grape Arbor Posts: bury, attach to concrete, or encase in concrete
 
Building a rectangular grape arbor in my backyard and thought Id knock some ideas around about the best way to make vertical 4x4 posts sturdy.

My options, in order of preference, seem to be:

Bury the posts:
Using this method I could afford to use 6x6 timbers, extra mass seems like it'd take longer to rot through. The soil is a thick rocky clay, so the posts are going to be solid in the earth. Although I'm a little concerned about rot/incests, even when using ground rated pressure treated.

Attach the posts to concrete anchors:
A little more pricey due to the connectors, but it seems like the 4x4s will last longer not being in the ground. I already purchased some deck connectors (PBS44 http://www.strongtie.com/products/connectors/PB-PBS.asp) but it's looking like they can't be used for a freestanding structure like a 4 post arbor.

Encase in concrete:
I've read online that this can either speed up or slow the decay of the post within them depending upon a few factors. Does anyone know a definitive answer to this? I honestly don't think concrete would help stability a tremendous amount with the otherwise hearty soil consistency here.

Ideally, I'd like something that would last a few decades before replacement and be less than about $20 per post. Thanks everyone!

Just Bill 01-23-2012 07:12 AM

I am assuming PT lumber??? For any climate that has a fair amount of moisture, I would not burry the posts. In concrete, maybe just the corner posts, for stability. But those posts will have problems sooner than if not surface mounted. In general, wood should never touch concrete or dirt, that increases rot, insect, issues.

shadetree 01-23-2012 03:28 PM

Pressure treated indeed.

That's kinda what I was afraid of; does anyone know if the Simpson Strong-Tie PBS44 would be suitable for something like this? Their website says: "Post bases do not provide adequate resistance to prevent members from rotating about the base and therefore are not recommended for non top-supported installations (such as fences or unbraced carports)." Which concerns me a little as this basically seems like a narrow, roofless, rectangular carport.

If the PBS44 won't work, does anyone know of a connector that will?

fixrite 01-23-2012 04:03 PM

there are post holders that actually cradle the posts. The post is slipped into the holder(about 18 to 24 inches) I have seen them at Home Depot. In fact there are 2 versions, one that the post sits in and the rest is solid, and the other one allows the post to be swivelled. The other end of the holder goes to a point and is cemented in place. If there ever is a need to replace it you can remove it from the holder and put in new post. I have not used them but they do look sturdy enough to do the job.

fixrite 01-23-2012 04:06 PM

the post holders are made by a company called "Peak products"

joecaption 01-23-2012 04:10 PM

No surface mounted post is going to work, None of the Simpson ties are sutable.
Pick up a vinyl post slip on post cover at Lowes.
Dig the hole just over 2' deep, pore some gravel in the hole for drainage, insert the 4X 4 with a 2 ft. section of post cover on it at the bottom. Back fill with concrete.
It will not rot and will not move.
Make sure to also use a post cap or at least cut the top at an angle.

concretemasonry 01-23-2012 06:22 PM

If you bury a post (PT ground contact) in a clay soil , either in with or without gravel, it will tend to deteriorate because the clay will contain the moisture and hold it around the post. The concrete itself does not cause deterioration but moisture can be transmitted to it from the clay soil. If you use concrete, form a slop on the top of the concrete to direct the water away from the post and exposed concrete.

Regarding the lateral stability, none of the connectors embedded or connected to concrete will really provide a lot of stability to a lightweight (wood nailed) structure unless there are diagonal braces somewhere.

To get lateral stability from an embedded post, you need depth and width. The wider or deeper the better. A post itself in gravel will not be a stable as a post embedded in concrete it the widths of the concrete and gravel are the same. Obviously, the deeper the better for the same width of the material around the post.

Once you have stability in the ground, the wood structure must be strong and stable enough to stand on its own. Keep in mind that water in the excavation can serious reduce the horizontal strength.

All of these principles apply to light use embedded posts and to steel 50'-150' high power transmission poles and everything in between. - For a fence, the lateral loads are not that important except for the ends gates and at corners or direction changes.

Dick

fixrite 01-23-2012 06:37 PM

http://www.homedepot.ca/product/deck...-finish/965688
This is the product I am talking about. Hope it helps solve your problem.

abracaboom 01-24-2012 09:37 AM

Quote:

Originally Posted by fixrite (Post 832549)
http://www.homedepot.ca/product/deck...-finish/965688
This is the product I am talking about. Hope it helps solve your problem.

Those might be OK for deck posts no longer than 2 feet, when you're too lazy to dig a hole and mix some concrete, but I would never use them with taller posts.

This will work: http://www.amazon.com/Simpson-Strong.../dp/B0044URPS2

Daniel Holzman 01-24-2012 09:57 AM

This is a grape arbor, not a house. People have been building grape arbors using direct burial of posts for a thousand years, I have seen them in Europe, and they are commonly done that way in New England. Certain species of wood are naturally pretty rot resistant, such as black locust, hophornbeam, and some varieties of cedar. If it were mine, and you are looking for a lifespan of say 15 or 20 years, I would direct bury the posts in sand or gravel and not worry about it.

My mailbox sits on a direct bury PT post, not even bedded in gravel, and it has lasted 15 years with no apparent deterioration. For a permanent structure, or one meant for human habitation, you need to use standoffs above concrete, else protect the wood against direct earth contact, but for a grape arbor, relax.

shadetree 01-24-2012 01:46 PM

Quote:

Originally Posted by Daniel Holzman (Post 833146)
This is a grape arbor, not a house. People have been building grape arbors using direct burial of posts for a thousand years, I have seen them in Europe, and they are commonly done that way in New England. Certain species of wood are naturally pretty rot resistant, such as black locust, hophornbeam, and some varieties of cedar. If it were mine, and you are looking for a lifespan of say 15 or 20 years, I would direct bury the posts in sand or gravel and not worry about it.

My mailbox sits on a direct bury PT post, not even bedded in gravel, and it has lasted 15 years with no apparent deterioration. For a permanent structure, or one meant for human habitation, you need to use standoffs above concrete, else protect the wood against direct earth contact, but for a grape arbor, relax.

That is kinda what I'm starting to think about this; all the structural bits are going to be exposed anyway & bolted vs nailed, so it shouldn't be too much of a PITA to just jack up one corner at a time replace them if they do rot out.

What do you guys think of encasing the bottom of the 4x4s with a vinyl post slip? Seems like it may help prevent a little bit of rot if the top of the slip sticks above soil level.

High Gear 01-24-2012 03:51 PM

I just rented a gas powered post hole digger and direct buried 6" round posts.

Watchout for the Japenese beatles they seem to go nuts over grape arbors.

ratherbefishing 01-24-2012 04:56 PM

When I moved into my house 20 years ago, I used my new circular saw to build a mailbox post out of PT 4x4s and buried it, direct contact with the dirt. It's still there. Hasn't even started to lean.

My new deck is sitting on footings, pilings poured into 10" tubes, Simpson connectors and 6x6s. But I walk around on my deck.

I'm with Mr Holzman on this one.


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