Rebar Placement In Dry Stack CMU

 
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Old 06-20-2007, 01:43 PM   #1
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Rebar Placement In Dry Stack CMU


I’m building a low (3') retaining wall that is essentially 3 sides of a square with 12' sides.

It wasn’t until I found this forum that I realized that I could drystack CMU and fill the voids and have just as strong a wall as a mortared one. So I’d like to build the wall that way since I’m a novice blocklayer and working mortar with a trowel is very time consuming for me.

My question is this:
Since the pressure on the wall is primarily horizontal (the earth pushing against the side) is it best to rebar in vertically in the cells or horizontally (using all bond beam blocks). Or maybe both? Or is that ridiculous overkill for a 3' wall? Would you use all bond beam blocks, or only in, say, the top (or bottom) course?

And I've filled voids before with Quickcrete. Is that ok? Or is mortar stronger?


Thanks for your help!

Sam

Last edited by SamGIII; 06-20-2007 at 04:31 PM.
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Old 06-20-2007, 01:49 PM   #2
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Re: Rebar Placement In Dry Stack CMU


You are mistaken in your assumpiton. You can have a surface bonded wall with horizontal and vertical reinforcement that will often outperform a normal masonry wall, but not a simple rack-and-stack and fill with concrete wall.

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Old 06-20-2007, 01:54 PM   #3
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Re: Rebar Placement In Dry Stack CMU


I see.

So I guess then my question would be is stacked and filled with concrete strong enough for a 3' retaining wall?
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Old 06-20-2007, 02:06 PM   #4
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Re: Rebar Placement In Dry Stack CMU


In my opinion, no. However, I have a very dim view of CMU used as a retaining wall under any circumstance, as that is not their intended use. Segmental Reaining Wall units are designed for that application and end up costing less and performing better.
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Old 06-20-2007, 02:22 PM   #5
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Re: Rebar Placement In Dry Stack CMU


TS is right.

Segmental retaining wall block look better and perform better for a 3' high wall than a rigid mass of concrete and grout. - No footing is required or suggested!

Also no rebar is required or suggested.

For ideas, look at the sites for the major segmental retaining walls systems (Allan Block, Anchor Block, Keystone and Versalok). They are available in most countries. If not there should be some "knock-off" brands available that would be adequate for such a small wall.
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Last edited by concretemasonry; 06-20-2007 at 02:27 PM.
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Old 06-20-2007, 03:36 PM   #6
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Re: Rebar Placement In Dry Stack CMU


I was trying to simplify my situation by calling it a "retaining" wall, but is not a landscape wall.

I've built a 7'X7' square spa out of CMU. All but about 16" of it is below grade. The plumbing runs around the outside of the CMU and I'd planned to "enclose" the plumbing with another 6" wide wall around three sides of it (the fourth side is against a bar/ BBQ). After the outer wall is complete, I would "cap" the two with concrete coping, finish the outside wall with brick veneer, esentially creating a sandwich (the inner wall being the vessel, the center space containing the plumbing, and the outer wall retaining the ground below grade--about 3' down--and simply for asthetics above grade--to enclose the plumbing.)

Hopefully that helps. Sorry about the confusion.
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Old 06-20-2007, 05:10 PM   #7
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Re: Rebar Placement In Dry Stack CMU


Never had a problem with a cmu wall.Your drystack method would probably be sufficient for 3' though it would be a lot stronger with mortar joints.
Use concrete mix for grout all bond beams and steel vertically and horizontal.I wouldn't use drystack for the spa.Why 2 walls?The pressure from the dirt would help counteract the water pressure.You'd be better off with 1 wall and beefing up the width.I would think maybe16"x16" with solid joints.
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Old 06-20-2007, 05:30 PM   #8
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Re: Rebar Placement In Dry Stack CMU


A cmu wall dumped full that short will always work for a wall that is only 3' tall. Any cmu wall higher requires footings, reinforcement, etc.

The "landscape walls" work for all applications much higher (up to 45') that a rigid concrete wall will not handle.
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Old 06-20-2007, 05:31 PM   #9
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Re: Rebar Placement In Dry Stack CMU


Yes, the spa (inside vessel) is already done and I did mortar all those joints AND fill all the voids with Quickcrete afterward, AND ran rebar horizontally and vertically throughout. At it's base (up to the seat) it's actually 24" thick(three courses make up the seat), above the seat it's all 6" bond beam block filled and rebarred as I mentioned. It really came out quite nice!

And yes, I've been toying with the idea of backfilling up to grade. I guess I keep thinking if there is any need to get back at the plumbing ever I could simply pop the coping cap off and have some (limited) access without ripping up the patio I plan to pour around the perimeter. If I backfill, pour the patio, and then build just a short wall to cover the above-grade plumbing, getting back to anything will mean lots of ripping up. But then on the other hand, what could I possibly fix in that narrow space 3 or 4' down anyway... hmmm...

Last edited by SamGIII; 06-20-2007 at 05:34 PM.
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Old 06-20-2007, 06:09 PM   #10
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Re: Rebar Placement In Dry Stack CMU


after you get enough posts ( i think you need 15) will you post a pic?
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Old 06-20-2007, 06:17 PM   #11
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Re: Rebar Placement In Dry Stack CMU


Haha! I would have from the beginning, but I don't have one on the computer I'm using at the moment. I'll post a few later today so y'all can tell me how crazy I am to build a spa out of CMU.
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Old 06-20-2007, 11:18 PM   #12
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Re: Rebar Placement In Dry Stack CMU


Ok, here's a design of what I hope to end up with(that's Google Sketchup, and is really cool!), and another of where I'm at at the moment. The more I think about it, the more I think maybe I might go with tkle and backfill to grade, and then go from there. But I'm always happy to hear from the experts!

Sam
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Old 06-20-2007, 11:20 PM   #13
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Re: Rebar Placement In Dry Stack CMU


I like it, it's fun!
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Old 06-21-2007, 05:41 AM   #14
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Re: Rebar Placement In Dry Stack CMU


Your plan will work for that application, but you will lose modularity with the brick if you drystack the CMU, if that matters.
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Old 06-21-2007, 07:16 AM   #15
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Re: Rebar Placement In Dry Stack CMU


Quote:
Originally Posted by SamGIII View Post
Ok, here's a design of what I hope to end up with(that's Google Sketchup, and is really cool!), and another of where I'm at at the moment. The more I think about it, the more I think maybe I might go with tkle and backfill to grade, and then go from there. But I'm always happy to hear from the experts!

Sam
Now that you've convinced me to do it your way.I wouldn't worry too much about future repair,not much will go wrong with PVC.Your mortared block look fine,I'd stick with it. Nice job.
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Old 06-21-2007, 10:42 AM   #16
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Re: Rebar Placement In Dry Stack CMU


Thanks for the compliments! I can tell you that while I'm saving A LOT of money doing it myself, I can for sure see the beauty of gunnite, cuz just the hole drilling (with a 3" masonry hole saw) took me more than a couple days and 3 pretty expensive bits! (I was also amazed BTW at the differences in how hard varying blocks from different sources were? Some would bore through in about a minute, some took 10 minutes!)

Anyway, I'm already revising my plans and will backfill to grade. (I pressure tested all the plumbing last night and it's good, so I think your right tkle, it should be fine.) And ya TS, I'm just going to continue to mortar the remaining block work--it's a great forearm workout, that's for sure!

Just finished the grouting, so 21 days to cure (while I plumb the equipment) and then I'm filling that baby up! Patio or no patio! haha!
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Old 06-21-2007, 05:34 PM   #17
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Re: Rebar Placement In Dry Stack CMU


Quote:
Originally Posted by SamGIII View Post
Thanks for the compliments! I can tell you that while I'm saving A LOT of money doing it myself, I can for sure see the beauty of gunnite, cuz just the hole drilling (with a 3" masonry hole saw) took me more than a couple days and 3 pretty expensive bits! (I was also amazed BTW at the differences in how hard varying blocks from different sources were? Some would bore through in about a minute, some took 10 minutes!)

Anyway, I'm already revising my plans and will backfill to grade. (I pressure tested all the plumbing last night and it's good, so I think your right tkle, it should be fine.) And ya TS, I'm just going to continue to mortar the remaining block work--it's a great forearm workout, that's for sure!

Just finished the grouting, so 21 days to cure (while I plumb the equipment) and then I'm filling that baby up! Patio or no patio! haha!
We'll be there.Who's buying the beer?

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