In a message dated 5/23/2007, [log in to unmask] writes:

The material that separates sidewalk concrete from buildings, light pole 
footings, etc.,  should not be tubular.  It should be the thickness of the slab, 
1/2" thick, and composed of something like asphalt-impregnated fiber, cork, 
plastic, or neoprene rubber.  My guess is that the "tubular stuff" that you 
mention is backing rod (often called backer rod".  Backer rod just will not 
function properly in this application.

I examined the installation more closely today (just before being forcefully 
informed by "George", the foreman, that it was unequivocally "illegal" to take 
pictures of "private property", notwithstanding the fact that he a) was 
unable to cite the law in question ("jus' look at de papers!") and b) that, after 
threatening to call the cops, he was suddenly unwilling to request assistance 
from a patrolmen who was about 30 feet away).   
 
There are three kinds of joints in play on this project (nwc 86th & Park).  
1) At the building/sidewalk joint there is a 1/2" joint, which is filled with 
caulk-type material.   
2) At intervals of three "flags", there is also a 1/2" joint, also filled 
with caulk.  
3) At the  sidewalk/curb joint, there is also a 1/2 " joint, but this is not 
filled with caulk, but rather a black, fibrous material - same material as 
cheap pipe insultation which was not set sufficiently low enough, and projects up 
enough that, in a few spots, it has been abraded so that the top 1/2" has 
parted from the body, and is flopping around like a Jersey tourist in a plaid 
leisure suit on Nantucket main street. 
4) There is a fourth kind of joint on this job, the kind Steve first alerted 
me to, saw cuts between the "flags".  Unlike the unversally-used tepid little 
depressions between "flags" - the kind you'd make with a pencil eraser at a 45 
degree angle, no deeper than 1/8 inch - these were, indeed, cut 1 or 2 deeep 
into the concrete.
 
I can see how this last joint - identified by Steve as the "control joints to 
deal with the cracks that form from shrinkage" - would indeed concentrate 
shrinkage cracks, instead of letting them run haywire.  
 
But these sawn joints are left unfilled (work was finished a week ago).   
Won't they allow water in and thus freeze-thaw damage?  Or, the work being done 
in May, the contractor (who is, in my experience, unique in making these saw 
cuts) counting on fillage by dog shit, grit, spittle and other sidewalk 
depositions?

Control joints can also be sawn into sidewalk and other concrete flatwork.  I 
won't go into that unless you insist, and maybe not even then.

Exception noted. 

But, the primary reason sidewalk concrete cracks is because of structural 
failure.  

Will control joints take care of these cracks?  Or only shrinkage?  And does 
the shrinkage happen in the first week or so?

Let me compliment you on using the term concrete instead of cement.  

It makes me feel cool, as if I could use those neat compressed air tools.  Or 
using the phrase "this application" which I will now adopt.  Just watch me.  
 
Christopher 



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