Contractors and DIY use groovers or saw cut control lines so that the
concrete will break at the joints. That's the plan but more lightly the
concrete slab will crack everywhere except at the joint lines. For the
concrete slabs I saw on patios, driveways and sidewalks, it seems pointless
to have control joints. Expansion joints excepted, off course.

So the question is, when concrete cracks then how do you make it break at
the control joints more often than elsewhere?

In article , "** Frank **" wrote:
Contractors and DIY use groovers or saw cut control lines so that the
concrete will break at the joints. That's the plan but more lightly the
concrete slab will crack everywhere except at the joint lines. For the
concrete slabs I saw on patios, driveways and sidewalks, it seems pointless
to have control joints. Expansion joints excepted, off course.

So the question is, when concrete cracks then how do you make it break at
the control joints more often than elsewhere?

It really depends on the specific situation but in general terms:

1. Prepare a proper foundation for the pour. If you pour concrete
on dirt, it'll likely crack all over the place.

2. Add steel mesh and/or rebar to each slab.

3. Use the appropriate mix and provide it with an opportunity
to cure properly (pay attention to temperature and moisture
levels).

4. Agitate and otherwise ensure a complete lack of large air
or water bubbles within the concrete itself (esp, around
any steel reinforcement).

If you do those things right, correctly sized slabs will not
crack.

--
|~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~|
| Malcolm Hoar "The more I practice, the luckier I get". |
| Gary Player. |
| http://www.malch.com/ Shpx gur PQN. |
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~~

On Oct 10, 1:14 pm, "** Frank **" wrote:
Contractors and DIY use groovers or saw cut control lines so that the
concrete will break at the joints. That's the plan but more lightly the
concrete slab will crack everywhere except at the joint lines. For the
concrete slabs I saw on patios, driveways and sidewalks, it seems pointless
to have control joints. Expansion joints excepted, off course.

So the question is, when concrete cracks then how do you make it break at
the control joints more often than elsewhere?


Depends the slab thickness but for a 5" slab......place cuts such that
you have 150 sq ft max panel size (try to keep the panels somewhat
squarish) & cut depth 1/4 to 1/3 of slab thickness, cut as soon as
concrete can be worked upon without damaging surface.

Too much water in the mix can cause shrinkage cracks that cuts will
not totally help avoid.

This should work out pretty well.

cheers
Bob

I don't know that I agree with Malcolm.

Good subgrade prep and compaction - yes. Nothing wrong with the
right kind of dirt, select fill preferred. No sod, no loam,

Mesh does not reinforce concrete.
Rebar in a 4" slab does not help, actually hurts.

Avoid re-entrant corners.
Concrete wants to be square, not rectangular.
Never exceed 12' in any direction without at least a contraction
joint, closer preferred.
Cut all contraction joints a minimum of T/4, that is, 1/4 or more
of the slab thickness. Most lumberyard jointers cut 1/4" deep.
Make sure the keel is at least 1" or you're wasting your time, I
prefer 1 1/2. If the contraction joints are sawed into the slab
(my preference) they must be sawed the same day as the pour as
soon as the concrete doesn't ravel under the blade. You CANNOT
wait and cut them the next day.
Curing the concrete is crucial. If you use a curing compound,
make sure it is compatible with potential floor
finishes/adhesives. A 3 day minimum full wet cure is the best.

--
______________________________
Keep the whole world singing . . . .
DanG (remove the sevens)




"** Frank **" wrote in message
. ..
Contractors and DIY use groovers or saw cut control lines so
that the concrete will break at the joints. That's the plan but
more lightly the concrete slab will crack everywhere except at
the joint lines. For the concrete slabs I saw on patios,
driveways and sidewalks, it seems pointless to have control
joints. Expansion joints excepted, off course.

So the question is, when concrete cracks then how do you make it
break at the control joints more often than elsewhere?

"DanG" wrote in message
...
I don't know that I agree with Malcolm.

Good subgrade prep and compaction - yes. Nothing wrong with the right
kind of dirt, select fill preferred. No sod, no loam,

Mesh does not reinforce concrete.
Rebar in a 4" slab does not help, actually hurts.


I'm about to redo a 4" slab, 3' wide sidewalk with rebar. If rebar (and mesh
as well) is not good, then what should be used?

Avoid re-entrant corners.
Concrete wants to be square, not rectangular.
Never exceed 12' in any direction without at least a contraction joint,
closer preferred.
Cut all contraction joints a minimum of T/4, that is, 1/4 or more of the
slab thickness. Most lumberyard jointers cut 1/4" deep. Make sure the
keel is at least 1" or you're wasting your time, I prefer 1 1/2. If the
contraction joints are sawed into the slab (my preference) they must be
sawed the same day as the pour as soon as the concrete doesn't ravel under
the blade. You CANNOT wait and cut them the next day.

Thanks for the pointer as I thought you could come back next morning and saw
away.

Curing the concrete is crucial. If you use a curing compound, make sure
it is compatible with potential floor finishes/adhesives. A 3 day minimum
full wet cure is the best.

--
______________________________
Keep the whole world singing . . . .
DanG (remove the sevens)




"** Frank **" wrote in message
. ..
Contractors and DIY use groovers or saw cut control lines so that the
concrete will break at the joints. That's the plan but more lightly the
concrete slab will crack everywhere except at the joint lines. For the
concrete slabs I saw on patios, driveways and sidewalks, it seems
pointless to have control joints. Expansion joints excepted, off course.

So the question is, when concrete cracks then how do you make it break at
the control joints more often than elsewhere?

Wow! Thanks to all, great information.

On Oct 11, 12:05 pm, "** Frank **" wrote:
"DanG" wrote in message

...

I don't know that I agree with Malcolm.

Good subgrade prep and compaction - yes. Nothing wrong with the right
kind of dirt, select fill preferred. No sod, no loam,

Mesh does not reinforce concrete.
Rebar in a 4" slab does not help, actually hurts.

I'm about to redo a 4" slab, 3' wide sidewalk with rebar. If rebar (and mesh
as well) is not good, then what should be used?

Avoid re-entrant corners.
Concrete wants to be square, not rectangular.
Never exceed 12' in any direction without at least a contraction joint,
closer preferred.
Cut all contraction joints a minimum of T/4, that is, 1/4 or more of the
slab thickness. Most lumberyard jointers cut 1/4" deep. Make sure the
keel is at least 1" or you're wasting your time, I prefer 1 1/2. If the
contraction joints are sawed into the slab (my preference) they must be
sawed the same day as the pour as soon as the concrete doesn't ravel under
the blade. You CANNOT wait and cut them the next day.

Thanks for the pointer as I thought you could come back next morning and saw
away.



Curing the concrete is crucial. If you use a curing compound, make sure
it is compatible with potential floor finishes/adhesives. A 3 day minimum
full wet cure is the best.

--
______________________________
Keep the whole world singing . . . .
DanG (remove the sevens)


"** Frank **" wrote in message
...
Contractors and DIY use groovers or saw cut control lines so that the
concrete will break at the joints. That's the plan but more lightly the
concrete slab will crack everywhere except at the joint lines. For the
concrete slabs I saw on patios, driveways and sidewalks, it seems
pointless to have control joints. Expansion joints excepted, off course.

So the question is, when concrete cracks then how do you make it break at
the control joints more often than elsewhere?- Hide quoted text -

- Show quoted text -

What exactly is the problem with coming back the next day and sawing
the control joints? Stamped concrete contractor did exactly that
with my patio and it worked. Only place I have a crack is in one
section where he should have placed another cut, but left the span too
long. One the second day, the concrete is only partially cured, and I
don't see how it could have shrunk enough to cause cracking.