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Main Question: I've been told that a concrete skirt (8" sloped pad) below the frost line and attached to the foundation via rebar is a good solution for putting pavers next to a block wall foundation that has had uncompacted backfill. Is this really a good idea or are there better ones?

My concern is that the concrete skirt could crack the cinder block with settlement over time. Without that solution, am I taking a huge risk that my pavers up to 3' out will settle over time and need fixed?

Project Background: I'm building an 18'x20' paver patio (19'x21' total to account for overflow) alongside my house. 18' will run parallel to the foundation, and the 20' will run out to the yard. The 3" high pavers will sit next to the cinder block foundation (No siding), and I'll have 1" of leveling sand underneath, followed by 6" of crushed 3/4" stone (Totalling 10" down from the finished height). Landscaping fabric will lay between the stone base and clay soil underneath. Note: The clay soil is full of shale, and the house is in Pennsylvania (So all seasons here).

Current Situation: I've dug out the clay/shale dirt to set the stone base in, but noticed around the foundation block that the soil had air pockets in it from all the shale scatter amongst it at various angles. There was a smaller concrete pad in that same place that I dug up previously due to cracking and having an improper base.

Current Advice Given To Me: A seasoned hardscaper told me most builders overdig the basement by about 2'-3', lay the foundation in, and then backfill the outside without compacting. No matter how old the house, that backfill will continue to settle. His suggestion was to make a concrete skirt down below the frost line that would support the stone base and pavers above if there were any settlement beneath the skirt.

His directions were to dig out 2-3' (Until you find the compacted soil past the backfill), 19' wide (The width of the base) and 44" down (Below the frost line and adding in the slab thickness). Afterwards, lay rebar down in a gridlike fashion (Drilling 4" into the cinder block to attach the rebar to the foundation). Next pour an 8" thick slab (Running the width and length of the hole) with a 1/4" slope finish that goes out to the compact soil. Let it cure, and then pour in 3/4" stone (Compacting every 2") until desire height for sand and pavers.

Picture Drawing For Reference Picture Reference of Concrete Skirt Below Frost Line (Note: Not Exact Scale)

Picture Reference of Concrete Skirt Below Frost Line (Note: Not Exact Scale)

  • Excellent question! Well written, lots of details, well organized. A poster-child for how to write a good question on SE. I'm shocked that you've not had any feedback on this yet, but I'm sure something is coming... – FreeMan Sep 23 at 14:30
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This can be a tough one to answer, I don’t like to pour next to block walls after seeing pours crack the walls.

always settling is kind of true as you add it compacts more but you want some voids in the gravel for water to flow. For me I would rather have to flip some pavers than take a chance of the angled pad cracking your wall as it settles.

I used to think all block walls leaked but realized it was mostly old block walls that had dirt and not rock back fill. I would recommend plastic sheeting at an angle like you planned with the concrete to slope away for drainage and to contain your sand. Then in 4-5 years add sand as it settles.

The pavers will also help to deflect water away from the wall but buy not having a solid mass of concrete there will be less lateral force on the wall and this may be your best option but you will probably need to add sand.

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  • Thank you so much @EdBeal for your input! Please bare with me as this is my first patio, but here are my thoughts: 1) I too thought it might be better to flip pavers and add sand, but the hardscaper advised I shouldn't add sand beyond the "1" max, and I should need to add stone instead (Making it a bit more work). 2) In the third paragraph (And this is just me not understanding) are you saying instead of concrete, use plastic sheeting (Is there a specific thickness) and lay that angled away from the house (At the depth of 44")? – Sean Sep 24 at 18:45
  • Here's a link about the 1" max sand: homeguides.sfgate.com/… – Sean Sep 24 at 18:48
  • What I am saying is to put plastic down over your rock so the sand doesn’t filter down into your rock and plug your foundation drains. With everything graded and a perimeter to hold the outer edge in place you can have several inches of sand 1” is my minimum to get a perfect patio with the slope a uniform thickness of sand and a premier board to hold everything in allows up to 3” of sand. The profile needs a slight grade even with pavers really helps if a tight fitting pattern I have had water travel across 20’ of pavers with no standing water but I did water seal it after putting it in Oregon – Ed Beal Sep 24 at 22:09

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