Concrete Chairs

[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?