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Old 03-18-2009, 11:25 PM   #1
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upright posts in a wet cement slab

we are laying a 22x22 cement slab this week. need upright posts on which to build our patio roof. my husband has never done this type of a job..........the three posts all obviously have to be in perfect alignment to attach the cross beams.......he thinks he lays the cement, THEN pushes in the posts after the cement settles a little. theres questions about making sure the posts are in a straight line....not just vertical. they can be vertical, but if we cant "connect the dots" to attach the top beams, we're still messed up. theres questions about how to do all the clean-up around the posts without messing up the rest of the slab. help??????????????????????? on top of all this i woul like to imprint some palm fronds into the cement for a design. hopefully this wouldnt be too risky.


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Old 03-18-2009, 11:51 PM   #2
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I'd opt for a post base in lieu of imbedding the posts in the concrete.

www.strongtie.com is a manufacturer of a number of different post base options.


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Old 03-19-2009, 12:57 AM   #3
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If these are wooden posts, I would not sink them in concrete - as already suggested use one of several post bases available. A post base can also raise the post a bit off the concrete to help keep the bottom of the post from deteroriating.

Once the concrete is poured measure where the posts should go and snap a chalk line. Drill holes (hammer drill with a concrete bit) for an expansion bolt. The post base fastens to the expansion bolt.
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Old 03-19-2009, 05:39 AM   #4
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This slab is not a DIY job to start with. Expect problems and it will take more work then you are thinking. Posts.. . lay out with a laser. Using a post support after cement is cured allows minor adjustments needed to get the posts in perfect alignment. Set anchor bolts accurately into the cement after it is first poured to provide a means of attachment of the post support latter. check that these anchors are square and lined up correctly.
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Old 03-19-2009, 06:08 AM   #5
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The others said it but maybe not the way I will say it. Posts need seperate support pads. That support should go to below your frost line, and the posts should not be set in concrete.

A slab floats on the ground. It has no foundation, so when the ground under it moves, so will the slab. If the posts are attached to the slab, they will move, also. Not a good thing for something connected to the house.
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Old 03-19-2009, 06:37 AM   #6
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Another thing is that the wooden posts will shrink and become loose in the concrete. Then you will have a pocket for water to accumulate. The posts may swell again from being wet, but will dry out and shrink again as well. Eventually the posts will decay. Make sure you put some control joints in a slab that size.
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Old 03-19-2009, 08:03 AM   #7
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Does your husband have any experience working with concrete?
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Old 03-19-2009, 11:06 AM   #8
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i don't see a happy ending here at all not knowing the proper way to do something then thinking it'll work = disaster eventually in anyone's book,,, no mention of footer/foundation - monopour-unipour-thicken'd edge-conventional footer & slab,,, not much's risky IF you know the basics & have some experience,,, 1st decide those questions THEN ask away !

ps - concrete is placed, finished, & cured, not laid then again, its not my $


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