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Old 08-01-2011, 11:17 PM   #1
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Deck posts and new concrete slab over?


Hello all,
I've just put in 12" footings at 42" deep and put the galvanized metal bracket on top of the footing to attach my 6x6 posts. These are all in place at this time. I set the height of the attachment to be below the new concrete slab that will be poured in a few weeks.

Is this good? or is there something I can correct or improve prior to pouring the new slab? my concerns of course are water getting down below the slab.
any advice would be appreciated.

Tony M.
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Old 08-01-2011, 11:34 PM   #2
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I might be misunderstanding but why didn't you just attach the posts to the new slab?
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Old 08-02-2011, 09:57 AM   #3
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I might be misunderstanding but why didn't you just attach the posts to the new slab?

Typically, where frost and snow loads are an issue, this would'nt be allowed.
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Old 08-02-2011, 09:59 AM   #4
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Ah, I've learned something. Don't have to deal with that in Texas!
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Old 08-02-2011, 06:47 PM   #5
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yes, my footing are 42" deep and 12" diameter. I'm going to have a 10X20 concrete slab installed to replace the original patio.

My question? The post-footing connection is apprx 4" below the anticipated concrete level. I took advice from a family member an now am having second guesses on weather this was the BEST way. Please if anyone has any info on the best solution from this point on, i'm all ears! What I imagined was that they can concrete over the footing, and around the post?
Any advice is appreciated.

Tony
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Old 08-02-2011, 06:58 PM   #6
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tony...not the best way to go about it. Posts should be above concrete to keep water from wicking into them. I suspect what you'll end up with is a 4" deep hole that wont drain and your posts wont dry out at the bottom causing them to rot.

Not sure of the best fix...one of the concrete guys will be along soon though.

Can you pour the slab lower?
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Old 08-02-2011, 07:11 PM   #7
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You could dowel rebar into the footers and pour the slab over it, hooking new strongtie brackets directly to the slab to put the posts in. That's they way we handle piers with pile caps in Texas and it seems applicable.
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Old 08-02-2011, 07:14 PM   #8
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12penny,
cant go any lower with the slab... maybe a couple of inches? What about concreting around the posts and having a slight lip... to prevent any water going down... and then sealing around the concrete to post contact?

tony
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Old 08-02-2011, 07:16 PM   #9
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Broughton,
Thanks for the reply.. I was thinking something along those lines also.
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Old 08-02-2011, 08:00 PM   #10
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We run into this all the time, and although it may not be the ideal situation, it still looks better than seeing the sonotubes sticking out through the slab at varying heights IMO. I would suggest wrapping a membrane around the post from the base to just above the concrete height. You can either cut it off at the concrete & caulk it later, or wrap the bottom of the posts to hide & protect the membrane.

One other thing to watch out for is to make sure that the concrete patio isn't sitting directly on the sonotubes. A slab on grade, like your patio, will see some movement through freeze-thaw cycles, especially at an exposed basement. Direct bearing on those sonotubes can lead the slab to cracking/breaking right over the sonotubes in the future.
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Old 08-04-2011, 02:47 PM   #11
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jomama45,
thanks for the response. What is membrane, and also, what do you suggest as far as separation from footings and slab.... should they just go thinner in those areas to prevent being on top, or is this something the concrete guys can figure out once they get here to pour? thanks again

Tony
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Old 08-04-2011, 06:36 PM   #12
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jomama45,
thanks for the response. What is membrane,

Self-adhering membrane like ice & water shield, or similar

and also, what do you suggest as far as separation from footings and slab....

I'd suggest at least 1" foam insulation if there's not much room, or a few inches of gravel if there's more room.

should they just go thinner in those areas to prevent being on top,

Definately NOT thinner than 3.5-4".

or is this something the concrete guys can figure out once they get here to pour? thanks again

Tony
If it's possible, we'll try to saw & break a little of the top few inches of the sonotube down lower. If these guys are decent, they should have an acceptable solution as well.
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Old 08-04-2011, 11:04 PM   #13
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move the post brackets onto the new slab surface. Temporary support your deck and then cut the posts to the new length needed. Dowel your existing piers and pour the slab allowing the new concrete to fill in on top of the piers. Be sure to embed new anchor bolts in the slab. Once the concrete has cured, install the new post base brackets and re-attach the posts. remove temporary supports and make yourself a cocktail to enjoy the new patio.

This is a similar concept to the lally column footings in basements. The footing is poured with the top being below the slab elevation and then the slab is poured over the top. The posts are put on the slab surface over the location of the footing.
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Old 08-04-2011, 11:13 PM   #14
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move the post brackets onto the new slab surface. Temporary support your deck and then cut the posts to the new length needed. Dowel your existing piers and pour the slab allowing the new concrete to fill in on top of the piers. Be sure to embed new anchor bolts in the slab. Once the concrete has cured, install the new post base brackets and re-attach the posts. remove temporary supports and make yourself a cocktail to enjoy the new patio.

This is a similar concept to the lally column footings in basements. The footing is poured with the top being below the slab elevation and then the slab is poured over the top. The posts are put on the slab surface over the location of the footing.
Not really the same thing at all. There should never be frost under a basement floor, and you certainly can expect frost under a patio in Illinois, especially one at an exposed basement...............
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Old 08-05-2011, 12:35 PM   #15
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Not really the same thing at all. There should never be frost under a basement floor, and you certainly can expect frost under a patio in Illinois, especially one at an exposed basement...............
You totally missed the point. I was comparing the ideas of having the load bearing footing (sono-tube in the post case, pier in the lally case) beneath a poured slab. Not the physical depths of footings and frosts. If frost heave of the patio slab is a potential issue then put in isolation joints around the column point similar to this: http://1.bp.blogspot.com/_QkdNftel7Y...t+DSC01118.jpg

how do you suppose you would replace the rotted out post using the wrapped membrane method? It will still be subjected to high levels of moisture as it won't be able to dry making it rot out long before the slab will need replacing.
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