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Old 05-21-2009, 08:50 PM   #1
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Suggestion for new sidewalk slab


As you can see from the attached image, I formed for a new slab in front of a set of concrete stairs down to the basement. The slab is going to be 5 inch thick and is only approximately 2 inches from the top of the first tread of the stairs. Before I dug up the soil and formed for the slab, there were two precast slabs on grade. Both were cracked and sunken due to wet area. The cracked slabs were approximately 6 inches from the top of the stairs, only because they sank. I know that the new slab should have about 6 iches drop the stairs, but the problems is that the grade at the bottom of the form will be much higher than the new slab. Should I install a small retaining wall there? Presently the new form puts the slab about 2 inches above the existing sidewalk. If I drop the form so to get the 6 inch drop at the stairs, the new slab will be lower than the existing sidewalk. Also as you can see in the image in the background, the old sidewalk that I want to regrade away from the house and replace with new precast slabs. How should I regrade this area? The area between the fence and the form desperately needs drainage. Any suggestions how I shold go about doing this?

Thank you in advance.
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Old 05-21-2009, 09:41 PM   #2
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Suggestion for new sidewalk slab


I would highly reccommend raising the forms to match the height of the existing top tread of the steps. If you leave that landing 2", or even 6" lower, I can guarantee you'll be left with a stumbling block. If your concern is the existing grade, either raise it or pour the concrete thicker at those edges.

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Old 05-21-2009, 10:26 PM   #3
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Suggestion for new sidewalk slab


Flyboy-Not sure if the previous post read your whole post. If those are your basement stairs UNDER NO CIRCUMSTANCES SHOULD YOU RAISE YOUR NEW POUR TO THE LEVEL OF THE TOP STEP! Especially with the grade conditions you show and describe, you would just be facillitating the transfer of your drainage problem down the stairs and into your basement. In a case like yours, if you can't change the grade (which can be complex and involve retaining walls and your neighbors) then you have to improve the drainage our your new poor is doomed to suffer the same wet fate as your sunken slabs. Chances are, a very simple French drain (little more than perforated drain tube, filter fabric and gravel) can divert the water that undermined your slab(s). The drain trench should be uphill from your stairs and parallel to them and the sunken slabs and ideally begin at or near the fence line in your picture and extend past the stair walls. Good luck!
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Old 05-22-2009, 09:36 AM   #4
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Suggestion for new sidewalk slab


Thanks for the replies buttersdad and jomama45

I've attached a couple sketches of what I think has to be done. I have no intentions of making the stair and slab even. Being in the architectural field I know there has to be a drop, but wasn't sure if I stay at 2 inches or go to the common practice of 6 inches. I decided to stay at 6 inches.
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Last edited by flyboy_ont; 05-22-2009 at 09:38 AM.
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Old 05-22-2009, 09:44 AM   #5
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Suggestion for new sidewalk slab


That looks like a good design. Couple of suggestions. Make sure the drain line you are installing daylights to a lower elevation than the bottom of the pipe. Second, even though you are draining the soil around the slab, you still should install a minimum of six inches of compacted crushed stone underneath the slab to promote free drainage under the slab, and to provide adequate support.
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Old 05-22-2009, 10:01 AM   #6
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Suggestion for new sidewalk slab


Thanks for the reply Daniel.

The space between houses does slope towards the front of the yard, so I should be OK there. I was going to be placing 2-3 inches of gravel, I should be using more? Also as seen in the photo, the existing sidewalk is very bad and I need to grade away from the foundation. Any ideas how I go about that?

Last edited by flyboy_ont; 05-22-2009 at 10:04 AM.
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Old 05-22-2009, 10:52 AM   #7
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Suggestion for new sidewalk slab


This seems to be a drainage problem. But on the information given, I can't tell where the water is coming from, where it wants to go, or where you would like for it to go. A plan view of the project with the surrounding elements with grades might be informative.

There is one thing I know for certain. There is no way I would build this with a walking surface as shown in red in the graphic below.



If there was no other way to control the drainage I would use a grate as shown below.

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Old 05-22-2009, 11:15 AM   #8
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Suggestion for new sidewalk slab


Thanks for the reply!

The is no way I can make the new slab and stair the same level. All rain and snow will run down the steps to basement level. There is a drain below, but if there is ever any debris there to cover the drain the area will flood and run into the basement interior. Unfortunately it is infeasible to put any kind of grating, there just isn't the room and no need for the slab even if I could get a grate in. I can not think of any other way of doing this. The step up to stair has been in place for nearly twenty years.

The present water problem is due to the neighbors yard. He has pulled up a section of his patio closest to the fence, leaving a hole to fill up with water. The patio is being redone in the next couple of weeks which should alleviate that problem.

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