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Pouring new concrete sidewalk over an...

Eric_McRory's picture

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I have a 75 year old sidewalk/walkway which has settled and cracked. I would like to pour new concrete over the old sidewalk to bring it back up to proper grade and at the same time avoid breaking up and disposing the old sidewalk. I have several questions:
1)How thick should the new concrete be?
2)What type of concrete should be used?
3)Should I use re-bar or wire mesh reinforcement in the new pour?
4)Should the old sidewalk be prepared in any way, such as cleaning with a chemical to achieve a better bond?

(post #170744, reply #2 of 7)

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Eric,

About 5 years ago,I had the same problem with a walkway going from my back porch to a gazebo in the back yard. I poured directly over the old walk with good results. My new pour was around 3" in most spots but as little as 2" or less in other spots. I cleaned the old concrete as best I could, without any chemicals, and in areas where the new concrete would not be very thick I applied a bonding agent to the old concrete ( it's a latex material, I believe). I used 80# bags of pre-mix and did the job myself over a three day period. The walk is about 60' long and about 2' wide. I used control joints at about 3' intervals but did not use rebar or wire mesh. It looks great after 5 years here in the upper mid-west. Good luck.

(post #170744, reply #3 of 7)

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I removed an in-ground fiberglass spa and plan to cover the area with a 14'x15' concrete slab. I am wondering whether I can back fill the 3-4 yard hole with broken concrete. Also, what kind of compacting should I employ with the broken concrete or if I choose to go with a straight soil back fill.

I removed about 2 yards of sand from the hole but I'm reluctant to use as fill since it may collect water and cause settling. Any Advise on this?

Thanks,
Gerry

(post #170744, reply #6 of 7)

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Steve,
You give good honest advice. Somehow I knew that the hardest way is the best way. I have very wet soil below the sidewalk, so what you said about laying a compacted bed of gravel makes sense, in order to avoid the frost heave.
Thankyou!
Eric.

(post #170744, reply #7 of 7)

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I have a 75 year old sidewalk/walkway which has settled and cracked. I would like to pour new concrete over the old sidewalk to bring it back up to proper grade and at the same time avoid breaking up and disposing the old sidewalk. I have several questions:
1)How thick should the new concrete be?
2)What type of concrete should be used?
3)Should I use re-bar or wire mesh reinforcement in the new pour?
4)Should the old sidewalk be prepared in any way, such as cleaning with a chemical to achieve a better bond?

(post #170744, reply #1 of 7)

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Eric,

Sidewalks are not forever. If yours have lasted 75 years they have given good service.

A new sidewalk should be 4" thick. Rebar and wire mesh are rarely used in sidewalks. There are two reasons for this. The first is that sidewalks do not carry a structural load so reinforcement is not required. The second is so that they can be easily removed when their useful life is over. Rebar and wiremesh will not prevent cracks. Properly placed control joints will not prevent cracks but they will help to ensure that the cracks occur in a controlled manner.

Sidewalks fail because they settle or frost heave. The solution to both problems is good support and drainage. Capping an old sidewalk is not a good idea. You should remove the old sidewalk and prepare a foundation of tamped (well compacted) sand, gravel, or dirt. The base material is determined by soil, drainage, and weather conditions in your area.

Concrete is expensive. The last load I bought was $65 a yard and it has gone up since. It will cost more in short loads. Forming and finishing is about $1 a sq ft. Expect to pay a premium if you have a small job. With this kind of money going out it pays to do the job right. Bust up the old sidewalk and start from scratch.

M2C

Steve

(post #170744, reply #4 of 7)

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I personally wouldn't use broken concrete for backfill - too many voids, and even if you put soil around and in between, water has a way of finding those voids and causing more settling than it's worth. Actually, you could have left the sand, depending on your soil underneath that. Even still, you can mix it with your good gravel for fill.

I would use at least 6" of good gravel under your new slab, prefepreferably12". Rent a walk behind compactor - it will probably cost you about $70 - 100 for the day, plus fuel.

Run it over your levelled area at least 6 times, until you have a firm base - depending on your backfill - you'll have to judge this.

(post #170744, reply #5 of 7)

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Hi there,

Pouring a new sidewalk over an existing one is a problem waiting to be solved in a future edition of breaktime.

Using concrete chunks as fill would also qualify for this honour.

Sometimes, the easy route works but most of the time it doesn't. Do remove the old and you will enjoy your new sidewalk for many years to come.

Gabe