Repairing cracks in expansion/control joints on sidewalk

Old 10-04-13, 02:45 PM
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Repairing cracks in expansion/control joints on sidewalk

I am attempting to repair various sized cracks on my driveway & sidewalk leading to the house.I have obtained backer rod of various sizes & Sikaflex for the smaller cracks in the sidewalk and also for the gap between foundation and concrete driveway which has shrunk/cracked and needs to be replaced.

The majority of cracks are smaller & workable with the exception of one crack approx: 1 1/2" wide & 3" deep after clearing out the weeds,grass & roots. I'm not sure what the proper method for making this repair is.
I've read various advice suggesting using sand or crushed stone to fill the majority of the gap before adding the backer rod,whereas some info states not to use sand as it will either wash away or retain moisture.

Also the section connecting the sidewalk to the driveway has one raised corner 1 1/4" high,the remainder of that "block" is level & sitting where it belongs.The crack is narrow enough to repair but I'm wondering how to repair this so it won't be a tripping hazard.Is there a concrete mix I can use to even it out down to a feather edge?

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Old 10-14-13, 08:56 PM
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I think using sand before installing backer rod isn't needed, and could possibly do some harm if saturated with water (from having an impervious base under it) and then being subject to a hard freeze. Just squeeze the appropriate-sized backer rods into the various gaps, and then install the Sikaflex. Follow the installation instructions, and leave it at least 1/4" low to prevent it from lifting up out of the joints come hot weather. You'll have best results if you sand-blast all joint faces before the backer rod goes in, to ensure good bond.

I'd correct the raised corner by simply grinding it off and smooth, using a masonry wheel on a large angle grinder. If you don't like the slick surface after grinding, give it a brush-off sand-blasting followed by a thin coat of neat Portland cement slurry, rubbed and worked in using a rubber float--done right, you will be able to closely match the abraded surface of the surrounding concrete. I've seen dozens of feather-edged concrete patch jobs over the years, and don't remember a single one that performed well or even looked close to decent.

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