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Concrete slab advice spebby_92 08-18-2007
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Posted by on August 18, 2007, 11:32 am
I am having a monolithic slab poured (25' x 30') with 16" (w) x
18" (d) footings. 18" is below the frost line in my area. This slab
will also have a 6" (h) x 4 1/2" (w) curb along the outside edge. I
am a little concerned about the quality of the work by the
contractor. My questions: Should the curb have re-bar? If so, what
size? There will be anchor bolts (j bolts) 4' o.c. along the curb.
How should the re-bar (#4 (1/2')) be set in the footings? By that I
mean how far below the surface should the top re-bar be? There are 4
lines of rebar in the footing, two near the bottom and two near the
top. In my layman opinion, the top set is too close to the surface.
Also, the re-bar is tied to a vertical length of rebar driven into the
ground. Is this acceptable? Any comment will be appreciated.


Posted by DanG on August 18, 2007, 7:21 pm
Rebar exposed to dirt should have 3 inches of cover. Formed
concrete should have 1 1/2" of cover. Most curbs do not have
steel. They do have load transfer dowels at joints - these are 1"
thick slick dowels about a foot long.

In commercial work, the 4 bars in the footing would typically have
#3 cages (stirrups) at a particular spacing, usually 12" c-c.
These beam reinforcements are usually hung in the forms, spaced
away from form surfaces, and poured.

The Corps of Engineers and other architectural concrete agencies
will not allow driving pins in the dirt to support reinforcement.
The contention is that said rebar will rust and the rust will get
into the rest of the reinforcement.

There are sure many installations on driven pins. I have dug up
old work that has been in the ground for over 50 years where the
rust had no gotten to the pins in the dirt, much less the grade
beam steel. I have dug up old footings, etc where the cage steel
was exposed to the dirt (was not spaced away and covered
properly), the rebar had rust, but was very viable.

Your call. It's your stuff. If the fellas are making an honest
effort at holding the steel to grade, providing temporary spacers
to keep the steel away from the dirt, plan to use a vibrator, and
can show other pours with a decent finish, I think I would leave
them alone. These issues should have all been resolved before
they ever started, to change now sounds like a recipe for
disaster.

--
______________________________
Keep the whole world singing . . . .
DanG (remove the sevens)
dgriff237@7cox.net



>I am having a monolithic slab poured (25' x 30') with 16" (w) x
> 18" (d) footings. 18" is below the frost line in my area. This
> slab
> will also have a 6" (h) x 4 1/2" (w) curb along the outside
> edge. I
> am a little concerned about the quality of the work by the
> contractor. My questions: Should the curb have re-bar? If so,
> what
> size? There will be anchor bolts (j bolts) 4' o.c. along the
> curb.
> How should the re-bar (#4 (1/2')) be set in the footings? By
> that I
> mean how far below the surface should the top re-bar be? There
> are 4
> lines of rebar in the footing, two near the bottom and two near
> the
> top. In my layman opinion, the top set is too close to the
> surface.
> Also, the re-bar is tied to a vertical length of rebar driven
> into the
> ground. Is this acceptable? Any comment will be appreciated.
>



Posted by on August 18, 2007, 8:43 pm
> Rebar exposed to dirt should have 3 inches of cover. Formed
> concrete should have 1 1/2" of cover. Most curbs do not have
> steel. They do have load transfer dowels at joints - these are 1"
> thick slick dowels about a foot long.
>
> In commercial work, the 4 bars in the footing would typically have
> #3 cages (stirrups) at a particular spacing, usually 12" c-c.
> These beam reinforcements are usually hung in the forms, spaced
> away from form surfaces, and poured.
>
> The Corps of Engineers and other architectural concrete agencies
> will not allow driving pins in the dirt to support reinforcement.
> The contention is that said rebar will rust and the rust will get
> into the rest of the reinforcement.
>
> There are sure many installations on driven pins. I have dug up
> old work that has been in the ground for over 50 years where the
> rust had no gotten to the pins in the dirt, much less the grade
> beam steel. I have dug up old footings, etc where the cage steel
> was exposed to the dirt (was not spaced away and covered
> properly), the rebar had rust, but was very viable.
>
> Your call. It's your stuff. If the fellas are making an honest
> effort at holding the steel to grade, providing temporary spacers
> to keep the steel away from the dirt, plan to use a vibrator, and
> can show other pours with a decent finish, I think I would leave
> them alone. These issues should have all been resolved before
> they ever started, to change now sounds like a recipe for
> disaster.
>
> --
> ______________________________
> Keep the whole world singing . . . .
> DanG (remove the sevens)
> dgriff...@7cox.net
>
>
>
>
>
> >I am having a monolithic slab poured (25' x 30') with 16" (w) x
> > 18" (d) footings. 18" is below the frost line in my area. This
> > slab
> > will also have a 6" (h) x 4 1/2" (w) curb along the outside
> > edge. I
> > am a little concerned about the quality of the work by the
> > contractor. My questions: Should the curb have re-bar? If so,
> > what
> > size? There will be anchor bolts (j bolts) 4' o.c. along the
> > curb.
> > How should the re-bar (#4 (1/2')) be set in the footings? By
> > that I
> > mean how far below the surface should the top re-bar be? There
> > are 4
> > lines of rebar in the footing, two near the bottom and two near
> > the
> > top. In my layman opinion, the top set is too close to the
> > surface.
> > Also, the re-bar is tied to a vertical length of rebar driven
> > into the
> > ground. Is this acceptable? Any comment will be appreciated.- Hide quoted
text -
>
> - Show quoted text -

Thank you very much DanG for that response. I know very little about
concrete work and thus don't know quality when I see it. Plumbing,
electrical and roofing I know well enough to make sure I'm getting a
quality job.


Posted by John Loomis on August 18, 2007, 10:34 pm
Hello,
I am a Concrete Contractor and Builder in Calif.
The footings should have re-bar in it spaced at least 3" clear of soil. The
re-bar near the top of the footing can be 3" or more.......
In a curb application, it is best to have the rebar in the curb since anchor
bolts will be attached in the concrete and used. The re-bar will hold the
curb together on the top of the slab.
Usually contractors try to support the steel from tie wire and hanging the
rebar from the top. concrete blocks can be placed on the bottom of the
footing and rebar placed on those.(3" dobies) One can also bend rebar to
support the upper bars in an L formation. It is tied to the bottom steel
and sticking up high enough to support and tied to the upper steel.
Diagrams for footings are easier to understand.
Rebar is the best for concrete slabs, footings, etc.
Neat work and tied neatly is best. 2' overlaps at splicing is best. (or 40
times the diameter is the right length for a splice.) 1/2" times 40 =
20".........
Thus the 2 foot rule more or less...........
I do a lot of slabs, sidewalks, foundations etc.
jloomis
>I am having a monolithic slab poured (25' x 30') with 16" (w) x
> 18" (d) footings. 18" is below the frost line in my area. This slab
> will also have a 6" (h) x 4 1/2" (w) curb along the outside edge. I
> am a little concerned about the quality of the work by the
> contractor. My questions: Should the curb have re-bar? If so, what
> size? There will be anchor bolts (j bolts) 4' o.c. along the curb.
> How should the re-bar (#4 (1/2')) be set in the footings? By that I
> mean how far below the surface should the top re-bar be? There are 4
> lines of rebar in the footing, two near the bottom and two near the
> top. In my layman opinion, the top set is too close to the surface.
> Also, the re-bar is tied to a vertical length of rebar driven into the
> ground. Is this acceptable? Any comment will be appreciated.
>



Posted by on August 22, 2007, 12:10 pm
> Hello,
> I am a Concrete Contractor and Builder in Calif.
> The footings should have re-bar in it spaced at least 3" clear of soil. The
> re-bar near the top of the footing can be 3" or more.......
> In a curb application, it is best to have the rebar in the curb since anchor
> bolts will be attached in the concrete and used. The re-bar will hold the
> curb together on the top of the slab.
> Usually contractors try to support the steel from tie wire and hanging the
> rebar from the top. concrete blocks can be placed on the bottom of the
> footing and rebar placed on those.(3" dobies) One can also bend rebar to
> support the upper bars in an L formation. It is tied to the bottom steel
> and sticking up high enough to support and tied to the upper steel.
> Diagrams for footings are easier to understand.
> Rebar is the best for concrete slabs, footings, etc.
> Neat work and tied neatly is best. 2' overlaps at splicing is best. (or 40
> times the diameter is the right length for a splice.) 1/2" times 40 =
> 20".........
> Thus the 2 foot rule more or less...........
> I do a lot of slabs, sidewalks, foundations etc.
>
>
>
>
> >I am having a monolithic slab poured (25' x 30') with 16" (w) x
> > 18" (d) footings. 18" is below the frost line in my area. This slab
> > will also have a 6" (h) x 4 1/2" (w) curb along the outside edge. I
> > am a little concerned about the quality of the work by the
> > contractor. My questions: Should the curb have re-bar? If so, what
> > size? There will be anchor bolts (j bolts) 4' o.c. along the curb.
> > How should the re-bar (#4 (1/2')) be set in the footings? By that I
> > mean how far below the surface should the top re-bar be? There are 4
> > lines of rebar in the footing, two near the bottom and two near the
> > top. In my layman opinion, the top set is too close to the surface.
> > Also, the re-bar is tied to a vertical length of rebar driven into the
> > ground. Is this acceptable? Any comment will be appreciated.- Hide quoted
text -
>
> - Show quoted text -

DanG, I have "fired" the contractor working on my slab and have opened
the door for the "recipe for disaster." I really had no choice. They
would show up without the tools they needed, for example, the day they
came to set the forms they had no spool of string. I loaned them
one. They would work an hour and then leave and I would have to call
to get then back after a day or two. Today I called and they told me
they were waiting on me, I was supposed to call and get the
inspection. The last time they were on site they said they needed to
go get a drill to set some dowels and it wasn't ready for inspection.
They were on site about an hour that day. I haven't seen them since.
The steel in place looks like a roller coaster, with portions higher
than the finished slab. They talk a good game but could not produce.
Nothing they said happened. This will probably wind up in court. I
have banned then from the site and told them I would call when they
could come get their steel and forms. With the footing dug, it will
be difficult to set new forms. Hopefully, I can find a contractor
willing to clean up the mess. Of course I;m looking at a delay of at
least 4 weeks. I contacted the guy you recommended but he never
returned my call.


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