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ciera 11-19-2008 07:32 AM

Repairing concrete sidewalk
One panel of our sidewalk is original stone (not concrete). However, there are some large cracks around it (where the stone and concrete meet) and there are some dish-like divots in the middle. Kind of like scaling, but on solid stone. The stone is also slightly lower than the surrounding sidewalk, so we're thinking we can just do an overlay. A couple questions though:

1) Will doing a concrete overlay on stone work?

2) How do we handle the large cracks and the shallow overlay? My understanding was we use the premix (with gravel already in it) for the large cracks, but several areas will be only 1/2 inch thick, so it seems like we can't use gravel. Do we use no gravel anywhere, or do we mix two batches (one with and one without) and layer them together?

3) Our books say to do concrete when it's 60-50 degrees. Looks like the weekend is not going to cooperate though. (They originally said 45, and now they're saying 30.) Can we still do this when it's cold? Any special precautions?

Our goal is not to have a long term solution, but at least get us through a couple years with something reasonably flat.


glennjanie 11-19-2008 01:08 PM

Welcome Ciera:
Standard concrete has to be at least 2" thick to keep from popping off. Putting it on the stone would be no problem otherwise.
There may be an exterior floor patching concrete product that will hold in a thinner situation but I don't know about it. You will need the higher temperatures either way.

ciera 11-19-2008 06:39 PM

Darn, so I basically have to hold off until warmer temps in April? The long range forecast is that we're getting a colder than normal winter, so if it's too cold this weekend, no hope until then I guess.

The book I have implied that a concrete overlay could be extremely thin, but it didn't say anything about a special product. I'll check into that though, thanks!

yesitsconcrete 11-29-2008 05:39 AM

temp's important when its below 40f when the work's best left to pro's,,, above 40, conc can safely be placed, finished, & cured by anyone w/good conc skills/knowledge/experience,,, caution - be certain temp won't drop below 40f & protect conc w/blankets to retain heat generated by curing ( hydration ),,, conc's exothermic yet it needs its created heat to complete the cure.

an overlay's possible using the correct mtls ( polymers, cement, fine aggregate, & water ) but its VERY tricky & i wouldn't suggest the work to anyone inexperienced,,, any jnts/crks present will reflect in the overlay.

1) Will doing a conc o'lay on stone work? possibly yes but, generally, no in your instance.

2) large crks & shallow o'lay? those crks have become working joints & should be addressed w/flexible sealant rather'n any mtl that has no elastomeric quality,,, in short, you cannot address 'em w/conc mix in a bag,,, layering different mix designs will only result in strength to the lever of the weakest mix.

3) see 1st paragraph

4) my best advice ? - post a sign saying ' watch your step ' :D & replace the stones when the weather's warmer ;)

ciera 11-30-2008 06:59 PM

Yeah, we're going to wait until spring now.

I should clarify. I did not mean to say stone work in the typical context. What I mean is that the sidewalk is stone. As in, one gigantic slab of stone, about 4 feet long and the width of the walk. (Slate, possibly? It's sedimentary and seems to have held up reasonably well given that it's been walked and rained on for a century.) Walking around the neighborhood, this seems to be original (turn of the 20th century). We also still have the stone curb, even in places where the sidewalk was replaced with concrete. (There's a strip of grass between them, so they don't always get replaced at the same time.)

The cracks are not in the middle of the stone. They're on the edge, where the stone meets the concrete. The stone and concrete is flaking away in those areas, made worse by the fact that plants started rooting in between them. I'll see if I can get a picture.

yesitsconcrete 12-02-2008 05:38 AM

possibly slate but, more likely, flagstone which was less expensive & MUCH more common to your/our area,,, our main entrance had a piece 8" thick & measured 10' square,,, conc should never 'touch' stone - instead, there should be a space between 'em which's then sealed w/backer rod & joint sealant, not caulk.

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