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 ************************************** See what's free at http://www.aol.com. -- To terminate puerile preservation prattling among pals and the uncoffee-ed, or to change your settings, go to: <http://listserv.icors.org/archives/bullamanka-pinheads.html>