Concrete Chairs

[EddieWalker]

One of the things I look for in pictures and videos of people pouring concrete, is if they use concrete chairs to hold the rebar off of the ground. If they are not using them, that's a huge red flag to me. The same thing if they are using wire instead of rebar, that's a red flag.

While watching some YouTube videos last night, it hit me that 100% of every commercial concrete job that I saw, they use Concrete Chairs.

The only people that do not use them are residential jobs, or home owners doing their own pours. To me, biggest lie told in concrete work is that they will pull it up while spreading it, and it will remain in the middle of the slab after being walked on.

 

[Chewwy]

One of the things I look for in pictures and videos of people pouring concrete, is if they use concrete chairs to hold the rebar off of the ground. If they are not using them, that's a huge red flag to me. The same thing if they are using wire instead of rebar, that's a red flag.

While watching some YouTube videos last night, it hit me that 100% of every commercial concrete job that I saw, they use Concrete Chairs.

The only people that do not use them are residential jobs, or home owners doing their own pours. To me, biggest lie told in concrete work is that they will pull it up while spreading it, and it will remain in the middle of the slab after being walked on.

A lot of residential work today (driveways and parking areas) involves using fiberglass reinforcement in lieu of either rebar or wire. Seems to be pretty standard in our area anyway.

 

[two_bit_score]

The same thing if they are using wire instead of rebar, that's a red flag.

I can see using wire on a sidewalk. I bet many residential sidewalks dont have it.

Everything else should have rebar. Do you prefer steel wire chairs or plastic?

 

[lilranch2001]

I find those chairs very difficult to sit on

 

[grsthegreat]

I always use steel chairs and rebar. Does not matter, cracks anyways.

 

[geblackwell]

One of the things I look for in pictures and videos of people pouring concrete, is if they use concrete chairs to hold the rebar off of the ground. If they are not using them, that's a huge red flag to me. The same thing if they are using wire instead of rebar, that's a red flag.

While watching some YouTube videos last night, it hit me that 100% of every commercial concrete job that I saw, they use Concrete Chairs.

The only people that do not use them are residential jobs, or home owners doing their own pours. To me, biggest lie told in concrete work is that they will pull it up while spreading it, and it will remain in the middle of the slab after being walked on.

Take a look at Concrete with the Hauses on youtube. Sometimes they do, sometimes not. They usually explain why or why not. They do pull the rebar if not on chairs. He is the concrete guy that everyone uses in that area (your go to guy.)
Perhaps in commercial there is an inspector on the job and they can not pour without it.
Seems like fiber rebar is the new thing.

 

[EddieWalker]

Take a look at Concrete with the Hauses on youtube. Sometimes they do, sometimes not. They usually explain why or why not. They do pull the rebar if not on chairs. He is the concrete guy that everyone uses in that area (your go to guy.)
Perhaps in commercial there is an inspector on the job and they can not pour without it.
Seems like fiber rebar is the new thing.

I just looked at their page and skimmed through 4 different videos of driveways that they poured. The good thing about them is how dry their mix is. It has great slump. They also do a nice job of finish work.

But I would never hire them because of they short cuts they are taking with rebar and wire. They didn't even lay out the rebar in a grid before pouring the concrete in one video. One guy was tossing rebar sticks into the concrete as it was being spread, just sort of spacing them by where they landed. Then they covered them up as they spread the concrete. None of it was tied together, and none of them where spaced evenly. That really shocked me. I've never seen anybody do that before!!!! Then the other driveways they had wire laying on the gravel. There was one guy with a hammer that bent over and hooked the wire, but it didn't come up, and a second later, they walked over it while spreading the concrete. 100% useless, but an excellent example of what not to do.

 

[EddieWalker]

Concrete cracks because of the water leaving the concrete as it cures. The more water that's added to the mix, the bigger the cracks. Another good example of commercial concrete jobs being better then residential is the amount of water that's used. In commercial jobs, they test it with a slump bucket, and sometimes, they take samples and let them cure, then put them through a press to measure how much strength it has. Nobody doing a driveway is testing their concrete, and sadly, almost everybody has concrete that isn't as strong as they paid for because of the amount of water added.

Fiber helps deal with the cracking from water, but it does not replace rebar. If you used fiber and didn't use rebar, and your concrete didn't crack, it's because they didn't add extra water. The fiber is only good for tiny, hairline cracks. They still happen, but the fiber holds the cracks together better so it's harder to see them.

Wire is great for walkways because nobody is walking on it. You just have to make sure it's in the middle to lower 1/3 of the pad. With walkways, it's easy to work the concrete and not walk on it. Walking on wire is why wire should never be used on anything wider then a walkway. It always gets pushed to the bottom of the concrete.

100% of every house that I've cut open the concrete slab of to relocated drain lines that has had cracks in the slab, also had wire at the bottom of the slab. I've never seen concrete issues where the rebar was in the middle of the slab.

 

[lilranch2001]

Concrete cracks because of the water leaving the concrete as it cures. The more water that's added to the mix, the bigger the cracks. Another good example of commercial concrete jobs being better then residential is the amount of water that's used. In commercial jobs, they test it with a slump bucket, and sometimes, they take samples and let them cure, then put them through a press to measure how much strength it has. Nobody doing a driveway is testing their concrete, and sadly, almost everybody has concrete that isn't as strong as they paid for because of the amount of water added.

Fiber helps deal with the cracking from water, but it does not replace rebar. If you used fiber and didn't use rebar, and your concrete didn't crack, it's because they didn't add extra water. The fiber is only good for tiny, hairline cracks. They still happen, but the fiber holds the cracks together better so it's harder to see them.

Wire is great for walkways because nobody is walking on it. You just have to make sure it's in the middle to lower 1/3 of the pad. With walkways, it's easy to work the concrete and not walk on it. Walking on wire is why wire should never be used on anything wider then a walkway. It always gets pushed to the bottom of the concrete.

100% of every house that I've cut open the concrete slab of to relocated drain lines that has had cracks in the slab, also had wife at the bottom of the slab. I've never seen concrete issues where the rebar was in the middle of the slab.

I hope “wife at the bottom of the slab” is a typo…..

 

[scootr]

I find whatever you use to suspend the reinforcement the bar or wire must be pulled up.
Step on a chair and it sinks down and stays down 99% of the time.
Fiber is okay. Fiber reinforced concrete still cracks and can move up or down on one side of the crack.
Rebar adds significantly more strength and tends to restrict vertical movement when cracked.
#10 wire mesh 6 o.c. is pretty stout - it's a good alternative for most small jobs.
Judging from 35 yrs of placing concrete from residential, multifamily, and govt work

 

[groundcover]

I was thinking differently too !

 

[two_bit_score]

I hope “wife at the bottom of the slab” is a typo…..

I did get a laugh out of reading that.

 

[two_bit_score]

wire mesh 6 o.c.

What exactly do you mean?

 

[two_bit_score]

100% of every house that I've cut open the concrete slab of to relocated drain lines that has had cracks in the slab, also had wife at the bottom of the slab. I've never seen concrete issues where the rebar was in the middle of the slab.

That is a very telling statement. It tells me that too many people don't know what they are buying and paying for. And seems like the more it happens the more people accept it. That is intolerable to me.

I looked at a nice house in a very good location at a decent price about 2 years ago. Wile I was talking to the selling broker I noticed a strange thing at the junction of a corner near the garage and the drive way. The drive way was either coming up and or the house was sinking at that spot. Very strange. I pointed it out and asked 'what's going on right here'? The selling broker looked me straight in the eye and said something like 'you are the only one who would ever notice that'. There was nothing on the seller's disclosure about settling or repaired slab. After looking more closely at the entire exterior I saw multiple cracks indicitive of an unstable slab. Both inside and outside. I also found out which foundation repair company had previously worked on the foundation in 10 different places.

Long story short the person who wound up buying the house put it back on the market in about a year of closing. They had done some cosmetic repairs inside and closed up the largest exterior crack at one corner. The house sold for almost $100k more than the buyer paid for it.

I still can't imagine how.

 

[lilranch2001]

That is a very telling statement. It tells me that too many people don't know what they are buying and paying for. And seems like the more it happens the more people accept it. That is intolerable to me.

I looked at a nice house in a very good location at a decent price about 2 years ago. Wile I was talking to the selling broker I noticed a strange thing at the junction of a corner near the garage and the drive way. The drive way was either coming up and or the house was sinking at that spot. Very strange. I pointed it out and asked 'what's going on right here'? The selling broker looked me straight in the eye and said something like 'you are the only one who would ever notice that'. There was nothing on the seller's disclosure about settling or repaired slab. After looking more closely at the entire exterior I saw multiple cracks indicitive of an unstable slab. Both inside and outside. I also found out which foundation repair company had previously worked on the foundation in 10 different places.

Long story short the person who wound up buying the house put it back on the market in about a year of closing. They had done some cosmetic repairs inside and closed up the largest exterior crack at one corner. The house sold for almost $100k more than the buyer paid for it.

I still can't imagine how.

People are stoooopid

 

[two_bit_score]

People are stoooopid

More like just uninformed. Extremely uninformed.

 

[lilranch2001]

More like just uninformed. Extremely uninformed.

That may be giving too much credit!

 

[ponytug]

There is a ton of experimental research that shows rebar needs to be 1/3 off the bottom of a pour, on chairs, and needs to be tied or welded together for maximum strength. There is a company that does metal spirals (think lathe swarf) and they claim near rebar strength, but it has to be gradually and thoroughly mixed in before boring, and the use case needs to be dry, I.e. indoors only. Expanded iron mesh concrete, aka ferroconcrete is incredibly strong, but does not lend itself well to large pours in my view.

Fiber only helps with surface cracking. It is not a replacement for tension strength in concrete. Lots of data on that one, too.

If you keep concrete wet, plastic sheeting, applied water, or immersion, it will continue to gain strength for a year. Six months of keeping it wet gets you about 80% of ultimate strength. Even a week of keeping the concrete covered and wet will buy you a great deal of additional strength.

There is recent data that the Romans mixed in quicklime just as they were mixing the polzzanic (volcanic ash) concrete, leaving small bits of quicklime. The quicklime fragments attract cracks, but then as water penetrates, the quicklime reacts with water and CO2 to seal the crack, which apparently explains the longevity of Roman concrete.

My observation is that a great deal of concrete work locally is suboptimal, with strength and longevity sacrificed for speed. Some of it is amazing; 100,000 sq.ft. warehouses level to less than 1/4" across the whole floor. Not many pours around here use galvanized rebar for ground contact concrete, nor anti-corrosion coated rebar, nor is there much attention paid to ensuring good, rapid drainage away from foundation or retaining walls. I had to go to a commercial wholesaler sixty miles away to get products for good drainage.

All the best,

Peter

 

[EddieWalker]

I hope “wife at the bottom of the slab” is a typo…..

Thanks, I changed it. That's funnier then "wire at the bottom of the slab"

 

[EddieWalker]

Lots of good information. My main point for this thread was from watching those YouTube videos and realizing that every single commercial pour that I saw on there, had chairs of some kind under the rebar. Then I watch residential pours and it's hit or miss on using chairs. Some do, a lot of them don't use chairs.

The ones who don't, all talk about pulling it up while spreading the concrete, then walk all over it. And if you watch enough of the video, you'll see that they only pull it up in the beginning, or just randomly when somebody seems to remember that they are filming.

I watched one video of a long driveway where the guy told one of his workers that his only job was to pull up the rebar. The guy had the tool to do it and in the beginning, he did pull it up a few times. Then later on, the boss would go find him and remind him to pull up the rebar. That was half way down the driveway. The same thing happened again, later in the video. And a few times during the video, the guy that was supposed to be pulling up chairs was pulling concrete, or just walking around in the background.

When I watch these videos, that's what I'm looking for. Who is pulling it up, and is it actually happening. The other thing besides noticing the slump, or how soupy it the concrete gets during the pour, I also watch where the rebar is while they are walking on it.

Stepping over rebar on chairs is a pain. It causes you to trip, it makes a hard job even harder. Same with water. Using extra water makes the job a lot easier, you get done faster, and everyone is paid the same, so why not cut those corners and have an easier day?