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Community and Q&A

Stamped concrete patio near foundation

Ryan Lambert | Posted in GBA Pro Help on

Hi all,

I have a couple of questions regarding a patio near the foundation of our house. My wife and I have been dealing with water issues in our basement/crawl space for a while now, and we just recently had a contractor in to seal the vent properly, install a membrane along the foundation wall, and add French drains tied into the downspout.

As the last part of this work, we have removed a surface deck that the old owners installed and are looking to install a stamped concrete patio with the same dimensions (14×30) pitched away from the home. Specifically my questions are:

– We want the patio as close as is reasonable to the crawl space and basement walls in order to keep the water out of there. I live in Ohio, so I’m assuming I need to account for freeze/thaw and heave, from my research. How close should my contractor for the patio place it to the house, and any recommendations on sealing that gap that will be left?

– The yard is a lot of clay and holds moisture, so we are considering installing drains around the perimeter of the patio to not only account for that but catch run-off from the pitch. Is gravel base sufficient in an environment like this or do we need to consider something additional?

Thank you!
Ryan

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Replies

  1. GBA Editor
    Martin Holladay | | #1

    Ryan,
    Q. "How close should my contractor for the patio place it to the house?"

    A. I think that a small gap as an expansion joint should work fine. This could be created by a strip of foam sill seal or perhaps 1/2" rigid foam (although concrete contractors may suggest a different material).

    Q. "Any recommendations on sealing that gap that will be left?"

    A. The gap could be raked out and sealed with a high-quality caulk.

    Q. "Is gravel base sufficient in an environment like this or do we need to consider something additional?"

    A. It's always a good idea to have a layer of crushed stone, at least 4 inches thick, under a concrete slab. Of course you will want a layer of 6-mil polyethylene directly under the concrete (to keep moisture away from your foundation). A continuous layer of rigid foam between the polyethylene and the crushed stone is optional; if you include it, it will reduce the chance of frost heaving.

  2. Joe Suhrada | | #2

    Everything Martin just said is true, and I second it. Add mesh that is tied together in there too for a tiny bit more money but make sure it is raised off the bottom. It will add strength to the concrete. Concrete strength is directly proportional to the amount of steel, properly placed in it. The half inch foam is a great idea and because you are only placing maybe ten inches or so, you might be able to scare up some scraps. Furthermore if you are ambitious, it gives you the opportunity to go deeper down the foundation wall if you have the energy to do some digging and place a few inches of foam a few feet down. Between that foam and the slab foam if you choose to put it in, you will be adding to the insulation value of your basement walls and the whole thing will help to keep the basement dry. Just remember to ask the guy who seals your stamped work to put some ground glass powder into the sealer because it makes it less slippery and stamped, sealed concrete can be a touch slippery when wet without it. You can but that powder at the home improvement store. Rust oleum might still make it.

  3. Ryan Lambert | | #3

    Martin and Joe,

    Thank you both very much for the informative answers. As someone still learning the ropes of home ownership, this forum is great.

    I had a brief conversation with my contractor today about the expansion joint and he was not going to include one by default since the patio was going to sit within an "L" (hugging basement wall as the lower part of L, crawl space as left portion) and have two free edges. He didn't have any issues including it, just said that he felt it wasn't necessary.

    I'd done some reading where it sounded like someone had a similar situation where the patio heaved and started pulling and cracking the foundation since it sealed right up to it. Not sure what your thoughts on that are. The fee to include the expansion joint was practically nothing, so I think we'll probably just include it for peace of mind regardless.

    Thanks again, really appreciate your help in making the right decision.

  4. James Morgan | | #4

    You don't mention the height of the new slab in relation to the lowest point of the house framing. If the house has siding beware of splash back issues which will be worse than with deck board, especially at concentrated flows like the angle of the L. The code minimum of 8" below framing might not be enough to prevent saturation and decay. Consider oversized gutters.

  5. KEVIN ZORSKI | | #5

    RYAN - If you use foam under the slab, you may want to extend it out beyond the slab to protect the outside edges from frost heave. In most of Maine, 2" of foam going out 2' beyond the slab edges takes care of it. ( zone 6). If you don't extend, frost can get under the foam. The foam here, in effect, is keeping the soil warm. Good luck to you.

  6. Ryan Lambert | | #6

    Hi James,

    I attached a couple pictures for reference. I have to repair a couple pieces of siding because they were cut for the deck install that is now removed, but if you're looking at the picture of the door, I was thinking of taking the patio about flush with the bottom of the lowest piece.

    Pardon the warped siding... previous owners liked to cook their house with their burgers.

    There is a decent sized overhang where the roof pitches into the gutters, then that downspout you see. The one thing I will mention is that up close picture appears to be the sill.. I'm not sure if I need to be considering that in my patio placement (does it need to be below sill?)

  7. John Kapp | | #7

    Having my floor resurfaced achieved great effects for my landscape. You should try it yourself!

  8. C L | | #8

    Oh my - based on that last photo, it appears we are looking directly at your framing, and that the top of your existing slab is about even with that bluish strip. Thus, based on this photo, you need to make sure the TOP of the new slab is at least 1/2" (some will say more) below the TOP of the existing slab. If not, there is no way for moisture in that wall to weep out, and the new slab risk trapping more moisture in there. Can you get a better picture of that condition in the last photo? Perhaps from a bit lower, with the gap illuminated or at least so we can see in that gap?

    So you have alot of dirt to remove in order to have a 4" slab, layer of poly and foam below that, and 4" of gravel below that.

    Oh, and for stamped concrete, you often get better results if you order a low bleedwater mix.
    While I agree with Martin's suggestion on the poly, that also tends to hold moisture in the concrete, forcing it to cure through the top. That sometimes causes some curl. You will want to counter that by having your contractor sawcut some control joints when the concrete is green. You will want those to be coordinated with your stamped pattern so it does not make it look like you paid for the stamping for naught...

  9. Drew Baden | | #9

    Ryan,

    I did something similar at my place in Northwest Ohio near Toledo.
    I installed a patio over clay back in 2001 and I wanted to make it last so I dug down 4' (Overkill: 3' is frost line here) and packed in crushed stone via gas powered vibrating tamper. Under all of this, I dug french drains to keep water that doesn't shed off the surface away from the house. This has been successful and my patio hasn't budged an inch. I'm just curious what part of Ohio do you reside?

  10. Joe Suhrada | | #10

    Ryan, did you lay geofabric under the gravel and above the clay?

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