Hi everyone, in regard to my garage floor. Yes I am going to place rebar. But what is your opinion on dobies vs pastic chairs vs slab bolsters. I have read the dobies are better. However the plastic chairs and slab bolsters allow for "holes" in the mix when poured, thus allowing a possibility of water penetration between the outline of the chairs or bolsters. Another engineering article stated the plastic chairs are better for contraction and expansion because plastic has the same properties as cement/concrete. Your opinions are greatly appreciated. Thank you in advance.
dobies vs plastic chairs vs slab bolsters
- Thread starter foodie
- Start date
ConCretin
Well-known member
Hey foodie. You are venturing into into the area of overthinking this thing. Any of the supports you mention are just fine. Just make sure the height is right to hold the bar in the middle third of the slab. Also, if you have a vapor barrier, you want a support with won’t poke through.
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larry4406
Well-known member
Sometimes our concrete contractor even uses small pieces of bricks to hold the bars/mesh.
wgasa84
Active member
No difference in what you're doing. We use dobie's in all of our pours flatwork.
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Thanks so much to all of you guys for your time and response. Yes I will definitely have a vapor barrier.
LLWillysfan,...you are so right!! I do over think everything,...but there is only one chance to do it right. And that is exactly what I was thinking in terms of what is less of a hassle so the contractor staff doesn't poke a hole in the vapor barrier and tip over the bar supports, despite the fact that they will be wired to the rebar. Have a great day everyone.
LLWillysfan,...you are so right!! I do over think everything,...but there is only one chance to do it right. And that is exactly what I was thinking in terms of what is less of a hassle so the contractor staff doesn't poke a hole in the vapor barrier and tip over the bar supports, despite the fact that they will be wired to the rebar. Have a great day everyone.
Radix2
Well-known member
How thick is your floor?
Heating pipe?
Heating pipe?
My floor is going to be 5 inches thick, no heating.
Jon_E
Well-known member
I used Lotel Mesh-Ups in my slab, supporting 6-gauge wire mesh sheets.
tapered-pin
Well-known member
order out a cube of concrete brick and use those.
tapered-pin
Well-known member
you mean the area that sees essentially no tension or compression?
reinforcing bar should always be in the lower 1/3 with no less than 1" of concrete all around it (preferably 2-3")
matt_i
Well-known member
I used Pro-Lok chairs, 2" tall in a 6" slab, for rebars 16" oc. Design for heavy machine-shop machinery and forklift rigging of same. Nothing but good to say about them, it definitely speeds up forming the grid. It looks like a weak thing but the bars snap in place quite well, as I recall I only lost 1 chair to splitting apart on the top. Home Depot had some of them but seemed like they were selling out/phasing out, my local lumberyard special ordered them for me. It seems like dobies are more of a west-coast thingy. I would have probably used those if I could have found them locally. The end result (of the wire-tied grid) was that it was solid and no person could have knocked it out of place, it was easy to walk over and not get "stuck". However it did require the pump truck for placement.
http://www.grip-rite.com/us/en/products/concrete-construction-products/prolok
http://www.grip-rite.com/us/en/products/concrete-construction-products/prolok
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ConCretin
Well-known member
you mean the area that sees essentially no tension or compression?
reinforcing bar should always be in the lower 1/3 with no less than 1" of concrete all around it (preferably 2-3")
You would be correct if we were talking about structural elements but we are talking about relatively thin, non-structural slabs on grade.
To start with, 1” of cover is not adequate for surfaces exposed to soil but even if you go with that, the middle third of a 4" slab starts 1.33” above sub grade so your example essentially locates the reinforcing in the middle third just as I suggest.
Secondly, a typical slab on grade is not thick enough to take advantage of the compressive strength of the concrete and the tensile strength of the rebar and act like a beam. It simply bends and cracks when loads are applied unless supported by the soils below.
Even if you question this, most structural cracks occur at the perimeter of the slab, where the top of the slab is in tension. Putting the rebar in the bottom does you no good here either.
Steel reinforcing in a slab on grade simply prevents cracks from opening up and displacing vertically. Rebar adds minimally to the slab's load bearing capacity until you get into much thicker sections.
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tapered-pin
Well-known member
then why use something as expensive as rebar when WWF sheets would suffice at a fraction of the cost.
lakeroadster
Well-known member
I'd respectfully disagree.
Voids in the concrete make the concrete weaker. Concrete will bond much better to concrete than it will to plastic.
Additionally, when the guys pouring the concrete walk all over the supports, the concrete dobies won't shatter and break like the plastic ones will. In this same vane, use 6 x 6-W2.9 x W2.9 welded wire mesh sheets (not rolls). It will spring back into place after it has been walked on. It's heavier than the 10 ga wire most of the big box stores use.
Therefore the concrete dobies are better than plastic chairs. Any support is better than no support, but why not use the best.
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ConCretin
Well-known member
I use rebar because it is more rigid and easier to support than wire. I think a lot of people use it with the mistaken understanding that they are getting a stronger floor.
Millions of square feet of commercial floor are placed every year with no steel reinforcing.
ConCretin
Well-known member
You might be right lakeroadster but I've been doing commercial/industrial concrete up here for 30 years and have never laid eyes on one. There are all kinds of ways to support to support reinforcing and I doubt anyone could tell the difference in the first 100 years or so. Might have to track down a pallet of them though and give em a try.
ConCretin
Well-known member
Alright lakeroadster, ya talked me into it. Called my main supply house yesterday. Said they'd never sold any but could get concrete dobies. Ordered a pallet to try. You're never too old for a good idea.
I usually just buy 2” thick ashlars, wack them with a hammer to break up into smaller pieces and place under the rebar as the pour is going along. That way the rebar is flat on the ground and wheelbarrows can roll right over. Many times supply yards will have a bunch of broken ashlars that they will just throw in as freebies
lakeroadster
Well-known member
Cool... Happy Dobieying
audioworks04
Well-known member
Mesh ups are the best thing to happen in flat work chairs. They can be walked on and not break and spring back up. Plastic castle chairs are a close second. Dobies cause voids due to a large piece of different material embedded in the mix. Any chairs with metal runners can allow moisture to work it’s way up to the reinforcing and cause it to rust.
But in the end anything that keeps the reinforcing up in the slab is better than it on the ground.
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Wow guys you are All amazing! Thanks so much for the discussion and responses. Audioworks 04, the Lotel mesh do look awesome, I just watched a video on them.
Matt i the pro lock chairs look great also. However, I just read an article from Molenaar North America, scientifically speaking they state that plastic spacers have a coefficient of friction 10 to 15 Times that of concrete. Plastic continues to expand and contract at higher temperatures. Dobies concrete spacers are the same material as the poured concrete so thermal contraction and expansion on are the same. This theory supports what Lakeroadster was stating. Who knew all of this goes into pouring a slab of concrete, wow.
The Molenaar company was describing their system of MoClips. These plastic spacers are placed at the top of the spacer and does not come in contact with the concrete . So essentially these are concrete dobies with a plastic clip on top. The plastic in the MoClip is only used for easily attaching the reinforcement, thus leaving the concrete part to do the work as the spacer. I have no idea if they work, but it certainly brings in the best of both worlds, easy of use and a dobie.
Matt i the pro lock chairs look great also. However, I just read an article from Molenaar North America, scientifically speaking they state that plastic spacers have a coefficient of friction 10 to 15 Times that of concrete. Plastic continues to expand and contract at higher temperatures. Dobies concrete spacers are the same material as the poured concrete so thermal contraction and expansion on are the same. This theory supports what Lakeroadster was stating. Who knew all of this goes into pouring a slab of concrete, wow.
The Molenaar company was describing their system of MoClips. These plastic spacers are placed at the top of the spacer and does not come in contact with the concrete . So essentially these are concrete dobies with a plastic clip on top. The plastic in the MoClip is only used for easily attaching the reinforcement, thus leaving the concrete part to do the work as the spacer. I have no idea if they work, but it certainly brings in the best of both worlds, easy of use and a dobie.
I have also read that everything you are stating is exactly true regarding the metal runners. But as a matter of discussion don’t the plastic chairs cause voids also. I don’t know I am just asking because as a matter of information to me and use of the best products. I would suppose it depends on what the dobies are truly made out of. Do you have any experience using the rebar-ups?... I saw those on the website also.
lakeroadster
Well-known member
Very astute observation foodie. Yes, any plastic style chair does create a void. As far as the concrete is concerned, each plastic support creates multiple stress risers.
However the concrete dobies adhere to the concrete, much like bricks adhere to mortar.
Technical data on dobies here>>>> http://daytonsuperior.com/docs/defa...e-dobie-tech-data-sheet.pdf?sfvrsn=416fb260_4
And Bar Support Handbook here >>> http://daytonsuperior.com/docs/default-source/handbooks/bar-support-handbook.pdf?sfvrsn=6dffd560_42
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Thanks so much lakeroadster! Yes, that makes sense how bricks adhere to mortar!! I will read the technical data. Thanks for the links and your time.
lakeroadster
Well-known member
2-1/2" would be fine. You want it within the middle 1/3 of slab but with 2" of cover.
From LLWillysfan https://www.garagejournal.com/forum/newreply.php?do=newreply&p=7002912
Which agrees with: http://www.concreteconstruction.net/_view-object?id=00000153-8bb4-dbf3-a177-9fbd50fe0000.
"Some authorities recommend placing the steel 2 inches below the top surface of the slab. Others recommend placing the steel one-third of the depth down from the top of the slab."
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redneckwheelan2
Member
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- Apr 4, 2013
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- 5
with using regular 2 inch dobie bricks it can put your rebar to high up if your grade isnt spot on and might poke threw the surface which is bad. if your using using #4 rebar that put the top of your rebar at approximately 3 inches. if your doing a 5 inch thick floor you can get away with 2 inch dobies. if your floor is under 5 inches thick you can use concrete patio paver bricks. they"re 1 to 1.5 inches thick and can also get them at the local menards.
one bad thing with having rebar within a inch of the surface is the rebar can get rusty and pop the surface off after enough winters.
one bad thing with having rebar within a inch of the surface is the rebar can get rusty and pop the surface off after enough winters.
lakeroadster
Well-known member
Dobies come in other heights than 2"... and the grade should be screeded to within +/- 1/4".
http://www.daytonsuperior.com/docs/...e-dobie-tech-data-sheet.pdf?sfvrsn=416fb260_4
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Ok so maybe a 6 inch floor is better in order to compensate for the dobies height? However, lakeroadster with the different heights available which one would you choose if doing a 5 inch floor? The engineer I hired for his specs recommended 6 inches of base with a minumin 4 inch floor in his written report. But in my discussion with him he stated a 5 or 6 inch floor. Now I am really torn. Any thoughts?.
lakeroadster
Well-known member
It really depends on what you will be using the slab for. Passenger cars, diesel work trucks, tractors, construction equipment or ?
I have a Rotary SPOA10 lift attached to the slab using epoxied 3/4" studs that specified 5.10" concrete thickness. So I used 5-1/2" thick - 4,000 PSI concrete, Angel Hair Mesh and Welded Wire Mesh 6 x 6 - W2.9 x W2.9 on 2" dobies in the bay where the lift is and 5" thick in the vehicle storage area.
mygarageone
Well-known member
Your correct about this , I have worked just about ever type of commercial job out there. No steel rebar or mess layer Down . Commercial contractors are now using the 4 wheel laser power screed machines , no way can they deal with rebar .
Over the yrs we have done Walmart’s , Kmarts , Sears stores ,shopping malls warehouses , water bottling plants , other than the outdoor loading docks , no reenforcement .