Rebar supports in a slab

   / Rebar supports in a slab #61  
No inspection on a garage floor here so I was on my own. I installed foam over the compacted base, then plastic before installing the rebar. Rather than 12"x12" squares, I used 10"x14" because it would be easier for my big feet. My concrete contractor warned me that plastic rebar chairs would sink into the foam, destroying all my hard work so I made my own out of concrete. They were a pyramid with a 2"x3" base,1 1/2" high, spaced evenly, using about 400 of them in an area of 1360 square feet. I installed the pex above the bar because it was too difficult to put it below. It was easy to walk around before the concrete was poured because of the size of the squares and then when the workers couldn't see the bar anymore, they would occasionally stumble but it didn't damage anything while they walked on top of the bar. This did require using a pump.

What did you use for forms to make your own rebar chairs? Did you mix your own concrete or buy pre mixed?
 
   / Rebar supports in a slab #62  
Maybe not as many as you. I'll stick with my contention. The mesh will end up in the bottom of the pour. And for clarity, I am referring to roll mesh. Panel mesh might react differently? If it is harder to push down thru the aggregate then it is also harder to pull up into the aggregate?

If there's a multi-man crew working, there will be very few square feet of pour that someone doesn't step on at one time or another during the pour.

FWIW...I have personally (many times) help pour slabs and it is not difficult at all to pulled rolled wire mesh up into the pour and it is done as the pour progresses so it is not trod on after the fact...there is a big difference between professional mechanics and amateurs employed as laborers...

Analogy...:
If you look at some arrowheads and spear points from several thousand years ago...they will be very precise and detailed...easy to see a lot of skill went into make them...now take a look at some arrowheads and spear points from just a few hundred years ago...you will see that compared to the older ones they are very crude and made just well enough to suffice...

Many trades/skills like concrete / flat work etc., etc... are the same as those arrowheads...the farther away from the absolute correct way to do something you get the the more inferior a product will become...

Those that learned from the onset that you did not just add water until you were happy with how easy a mix would pour and how to use the wire hooks on their pulls to keep the mesh up in the pour...I remember on a lot of slabs the architect or engineer would specify that all pours over so many square feet were to be covered with burlap and kept wet for the first 3 days after the pour...

One of the main reasons for the decay in the accepted on site skill levels and quality controls in the concrete industry is by its own nature a cover up...once the pour is made everything is hidden and inaccessible...out of sight is out of mind...move on to the next one...this is mostly observed in the residential sector of the industry...most commercial contracts (and bank loans) require on site testing and test cylinders poured for followup sign offs...

FWIW...to test existing concrete for compression (see if too much water was added when it was poured)...you can buy or rent what is called a "Swiss Hammer"...it is a device that will tell you within reason how durable your slab etc. is ...
 
   / Rebar supports in a slab #63  
FWIW...I have personally (many times) help pour slabs and it is not difficult at all to pulled rolled wire mesh up into the pour and it is done as the pour progresses so it is not trod on after the fact...there is a big difference between professional mechanics and amateurs employed as laborers...

Analogy...:
If you look at some arrowheads and spear points from several thousand years ago...they will be very precise and detailed...easy to see a lot of skill went into make them...now take a look at some arrowheads and spear points from just a few hundred years ago...you will see that compared to the older ones they are very crude and made just well enough to suffice...

Many trades/skills like concrete / flat work etc., etc... are the same as those arrowheads...the farther away from the absolute correct way to do something you get the the more inferior a product will become...

Those that learned from the onset that you did not just add water until you were happy with how easy a mix would pour and how to use the wire hooks on their pulls to keep the mesh up in the pour...I remember on a lot of slabs the architect or engineer would specify that all pours over so many square feet were to be covered with burlap and kept wet for the first 3 days after the pour...

One of the main reasons for the decay in the accepted on site skill levels and quality controls in the concrete industry is by its own nature a cover up...once the pour is made everything is hidden and inaccessible...out of sight is out of mind...move on to the next one...this is mostly observed in the residential sector of the industry...most commercial contracts (and bank loans) require on site testing and test cylinders poured for followup sign offs...

FWIW...to test existing concrete for compression (see if too much water was added when it was poured)...you can buy or rent what is called a "Swiss Hammer"...it is a device that will tell you within reason how durable your slab etc. is ...
Burlap’s is still used for construction joints
Swiss hammer commonly called Schmidt hammer is not a good tool to tell if excess water is used in slab
 
   / Rebar supports in a slab #64  
Burlap痴 is still used for construction joints
Swiss hammer commonly called Schmidt hammer is not a good tool to tell if excess water is used in slab

Honestly it's a tool that is only an indicator...its results are often inconclusive...it's just a device that gives some insight into the durability of concrete after the fact...

Since the strength of concrete is directly related to the water/cement ratio...any indication of weakness points to a too high water content at the time of the pour... the Swiss Hammer test does not require any sampling (i.e., sawing out test sections for compression testing)...it was really just an off the cuff remark...people outside the industry are no likely to even know about a Swiss Hammer...:D
 
   / Rebar supports in a slab #65  
I'll stick with my first opinion. Forget mesh. Properly use rebar. Very, very, very few contractors will pull mesh enough to be effective. Generally, it will end up at the bottom of the pour.

As Pine pointed out, it's hard to know what you got in the end because you can't see it. So,,,,,, design it for the best chance of success. Mesh is not it. If you think your contractor can walk on your pour without tromping everything that's not secured to the bottom of the pour is naive. Doesn't matter how many pours you or I have witnessed, participated in or simply want to talk about. :)
 
   / Rebar supports in a slab #66  
Concrete slab reinforcement is all about "live loads"...that is what they are designed for...using more reinforcement than is needed by design is a waste regardless of how it may be rationalized...
Except directly under load bearing structures there is no need for anything more than wire mesh and or fiberglass etc. fibers in a typical residential home floor slab...

Multi level parking garage floors and ramps require a little more reinforcing...:D
 
   / Rebar supports in a slab #67  
Concrete slab reinforcement is all about "live loads"...that is what they are designed for...using more reinforcement than is needed by design is a waste regardless of how it may be rationalized...
Except directly under load bearing structures there is no need for anything more than wire mesh and or fiberglass etc. fibers in a typical residential home floor slab...

Multi level parking garage floors and ramps require a little more reinforcing...:D

Yup......correct!
 
   / Rebar supports in a slab #68  
What did you use for forms to make your own rebar chairs? Did you mix your own concrete or buy pre mixed?

I used a 2x6 and added angled sides to it to make a V shape form with a flat bottom and then stapled a crude piece of 1/2 round to the centre of the flat bottom. I mixed the concrete in a bucket with a home-made paddle mixer and then cut the pieces to length with a diamond blade in my skill saw. Yes it was a lot of work but my floor cost me about $10,000.00 and I couldn't afford to take any chances. 001.JPG002.JPG003.JPG
 
   / Rebar supports in a slab #69  
I used a 2x6 and added angled sides to it to make a V shape form with a flat bottom and then stapled a crude piece of 1/2 round to the centre of the flat bottom. I mixed the concrete in a bucket with a home-made paddle mixer and then cut the pieces to length with a diamond blade in my skill saw. Yes it was a lot of work but my floor cost me about $10,000.00 and I couldn't afford to take any chances. View attachment 687113View attachment 687114View attachment 687115

A good plan that worked well!
 
   / Rebar supports in a slab #70  
I used a 2x6 and added angled sides to it to make a V shape form with a flat bottom and then stapled a crude piece of 1/2 round to the centre of the flat bottom. I mixed the concrete in a bucket with a home-made paddle mixer and then cut the pieces to length with a diamond blade in my skill saw. Yes it was a lot of work but my floor cost me about $10,000.00 and I couldn't afford to take any chances. View attachment 687113View attachment 687114View attachment 687115

That's a good way to save some dollars. I'm no expert but I always wondered if some designs/brands of the plastic chairs made a void or weak spot in the concrete.
 

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