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.