Setting A Post In Concrete Against An Existing Slabs - Concrete, Stone & Masonry - DIY Chatroom Home Improvement Forum

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Old 06-19-2020, 08:46 AM   #1
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Setting a post in concrete against an existing slabs

I am installing a heavy duty gate (2-sided with 10 foot wide panels that swing to create a 20 foot opening).

This is my first post, so I can't post a link for the example picture, but it is at

The steel posts on either side of the gate are supposed to be set in 18" diameter 48" deep concrete. My question is this...

How would I set them tight against an existing concrete slab. I would like them both set tight to the alley behind my home, and one of them in the corner where the alley slab meets my driveway apron. Is there a best-practice for doing this?

I live in Wisconsin, so we have some significant freezing/thawing and I really don't want them to move.

After the posts are set, I am planning on having a new slab poured, that will fill the space between the gate posts. I would like the new slab to be poured up to (and around) the gate posts, but not sure how to deal with the heaving of the new slab relative to the posts and post footings.

I actually have this issue in several spots, where I want fence posts on the edge of the new slab. I was planning to pour my fence post concrete early and a little low, and then top off with the slab pour, but that doesn't give me an expansion joint around the post footing. I am putting an inground basketball post up as well, same there.

One idea I had was to set sonotubes for all of my posts, with the cardboard tube higher than eventual level of the concrete, then trim the tops of the tubes flush to the slab level later - but it would be difficult to match the concrete level inside and outside of the tube.

I would really appreciate some advice.

Thanks for the help!
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Old 06-19-2020, 10:50 AM   #2
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Re: Setting a post in concrete against an existing slabs

You want to tube high to brace them in place, just poke some nails thru to mark the fill height.
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existing concrete slab , expansion joints , footings , heave , posts in concrete

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