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Discussion Starter #1
Im getting ready to pour a new slab 21' wide by 20' long, and am going to build a awning over part of it 15' long by 19' wide. It will be supported with 6x6 posts. My question is I live in Kansas and have to get the footings below the frost line, Im sure I need to isolate the piers from the slab with some expansion joint due to frost heave on the slab and the piers not moving at the same rate which would cause cracks. How should a person do this though? Im pouring a colored concrete patio so I cant pour the piers to slab level then put expansion around them before pouring the slab because then it wont match the slab color (Ill be hand mixing piers and cant color the same as concrete company will be doing). Confused on how to isolate piers and slab but have concrete match in both?
 

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Concrete & Masonry
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It's not ideal, but the easiest approach would be to pour the tubes 6-8" below the top of the new, future patio, set the posts in right away, and pour the patio around them. The down side is that the posts will be below grade and are likelier to rot out faster. Make sure there is good, soft expansion foam around all 4 sides of each 6x6, as these areas are prone to cracking that close to the edge. I'd highly recommend working the control joints pattern in the patio around the posts as well...........
 

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Discussion Starter #3
The owner of my local building supply store tells me to just dig down 24 inches, which I don't think is deep enough for norther kansas, maybe it is? But then he says to just pour the slab right over them and that will work just fine without cracking. Don't sound quite right to me
 

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The reason it doesn't sound right is because it isn't. Imagine the patio being subjected to frost heave in winter (extremely common in full exposure situations). Do you think a couple of sono tubes 24" down will keep Mother Nature from lifting the patio at varying heights???
 

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Discussion Starter #5
Exactly what I said to him, but whatever as long as I do it right. Is 24" deep enough for 12" sonotube in northern kansas??
I wondered if I pour my pier to grade, make a round form out of 1/2 inch rubber expansion joint the same size as sonotube and sitting on top of the tube and level the top of the expansion joint to the top of the slab then pour the whole slab and top of pier at the same time so that color would match. It would isolate the pier and would allow me to attach my post at slab level. Is it really worth doing all that or just use the post through slab method mentioned above?
 

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Exactly what I said to him, but whatever as long as I do it right. Is 24" deep enough for 12" sonotube in northern kansas??

Not positive, but I would think it would be closer to 48" deep....

I wondered if I pour my pier to grade, make a round form out of 1/2 inch rubber expansion joint the same size as sonotube and sitting on top of the tube and level the top of the expansion joint to the top of the slab then pour the whole slab and top of pier at the same time so that color would match. It would isolate the pier and would allow me to attach my post at slab level.

You'd need to make sure the second pour was at least 6" thick or so, and they'd likely have to be doweled together. Uplift from high winds is likely as big a concern as frost heave where you're located...


Is it really worth doing all that or just use the post through slab method mentioned above?
I guess everyone has differing opinions on this, but we typically pour around the 6x6's directly........
 

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Discussion Starter #7 (Edited)
Heres a rough paint drawing of control joints. would this be ok to prevent cracking around the post or would it be better to have the joints off the corners? The joint on the left side isn't very long and I don't want it to be a problem area having the post so close to the edge. what do you think??

Image doesn't seem to enlarge for me so here are the numbers on the left side top to bottom 1'3", 8'6", 5' and the right side top to bottom 6', 6x6 post, 3'6" and the bottom number in the middle is 21'
 

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Concrete & Masonry
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At a minimum, I'd run the control joint from left to right in that picture, I wouldn't run them the other way as you'll end up with such small, narrow sections that can create more issues. To be perfectly honest, your image isn't real clear, so I can't comment on exactly where I'd put them. I can say w/o doubt though, make sure you use some decent expansion material like this around the posts:

http://www.wrmeadows.com/deck-o-foam-expansion-joint-filler/
 

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Discussion Starter #9 (Edited)
I'm sorry, I should of said the control joints I was thinking of are in red. What do you think of the placement? Sounds like i many have too many? I just want to be carefull around the post and do my best to keep it from cracking. I could do all the ones left to right like you said and one down the middle maybe top to bottom that would keep it In 11 foot section from left side to right side
 

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I'm afraid I would try to form up for the piers so that the tops are level with the top of the slab.

Say you use sonatubes. Set them level with the top of the slab and secure them with forms, then backfill them so they don't move around. Now remove the forms. Wrap 2 layers of the foam expansion/contraction stuff around them, the type with the 1/2 rip strip on top.

Now pour the slab and the sonatubes at the same time, and screed and finish right over the top. Drop your J bolts in as you pass with the screed. You'll have to finish around the J bolts, but it will be nice to screed right through without working around anything.

When you are done, rip off the top of the expansion/contraction foam and the paper around the sonatube and fill the space with some self-leveling caulk stuff.

The brackets you install for the 6x6 posts will hold the posts up about an inch above the concrete slab, so you should be good there. And the 1" expansion joint around the piers should make you good there as well.
 

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As far as control joints go what you have looks pretty good but concrete is going to crack where it wants to anyway. Also cracks always want to start from interior corners so they should end there if possible.
 
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