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Thread: Gap under concrete border/deck

  1. Back To Top    #1

    Join Date
    Jun 2010
    Location
    Toronto, Canada
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    34

    Question Gap under concrete border/deck

    We have a 4 foot concrete border/deck that surrounds our pool which is then surrounded by our lawn. Late last year I saw both a racoon and a rabbit disappear into an opening where the lawn met the concrete border. At the time I thought they had dug out a bit of earth from under the concrete border and were using that area for shelter.

    Fast forward to today and I finally decided to see if I could fill in these two openings and see if they did any damage. However, after digging a trench along one side of the concrete border and looking underneath I discovered there is about a half foot opening from the bottom of the concrete to the earth below it that extends most of the way around the pool. I'm assuming the earth settled this far down since the original owner had the pool built, but now I'm not sure what I should do. Is this something that people live with or do they fill in that gap if it develops over time. If so, what would I use to fill it in (soil, sand, stone etc)?


    Here are some pics that give a better idea of what it looks like:



    Here's the concrete border:





    This is the trench I dug so I could see under the concrete:





    Here is the gap under the concrete showing the pool wall at the back, the concrete/stone mixture on top and the earth on the bottom:





    Another view of the gap:

    20,000 Gallons Inground Vinyl Pool, 1 skimmer, 1 floor drain, 4 return jets, 1 vacuum intake
    Hayward Vari-Flo XL sand filter (SM2506T), Hayward EZ Flow Pump (SP-3107X10), Emerson Pump Motor (EB228), Hayward Comfortzone NG Heater, Hayward Chlorinator (CL220)

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    Join Date
    Sep 2015
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    Tucson, Arizona
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    Re: Gap under concrete border/deck

    I'd fill the gap. It looks big enough that the concrete isn't supported and seems like its only a matter of time before it cracks if not catastrophically fails. I don't know what is best to use to fill it, because it seems like you need to compact whatever you do use so that is fully supports the concrete.
    Owner Build. 32x16, with 6x8 raised spa. Broke ground April 1, 2016, swimming July 18. Pentair Intelliflo VS + Whisperflo for Water features; Clean & Clear Filter 420; Master Temp Heater 400k BTU; Intellibrite 120V pool and spa lights; Regular ol' plaster.

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    Join Date
    Apr 2016
    Location
    Houston, TX
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    206

    Re: Gap under concrete border/deck

    Fill it in with sand, sand is thin all will fill all the small spaces down there, sand then water it down to push sand down as far as it can and repeat until it covered

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    bmoreswim's Avatar
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    Jul 2012
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    Central MD
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    Re: Gap under concrete border/deck

    Mudjacking came to mind. I also thought of foam, then I searched. This could be a solution...

    http://concretejack.com/erosion-under-concrete/

    One of their scrolling pictures shows your exact situation.

    But obviously any solution that someone else has to do will be more expensive than something you can do yourself. However, solutions you can do yourself have a greater likelihood of being less effective than those done by someone with the right equipment. Often times that's the conundrum.
    18'x38' Rectangle (3'-8 1/2' deep w/ diving board) - 27K gal. w/ gray plaster
    Hayward equipment (cartridge filter, 2-speed pump, SWCG, automation) View Our Build
    Coverstar automatic pool cover | StoneMakers concrete retaining wall and decking
    Spring 2013 Build | Dolphin Active 20 robot cleaner | Support TFP!

  5. Back To Top    #5

    Join Date
    Jul 2015
    Location
    Naperville/Illinois
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    18

    Re: Gap under concrete border/deck

    I have the similar problem. Does anyone know of a business who can correct the sinking around the pool in northwest suburbs of Chicago?

  6. Back To Top    #6

    Join Date
    Jan 2016
    Location
    Mesa, Az
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    536

    Re: Gap under concrete border/deck

    Is that a gunite pool or liner? If it is gunite, you could pour CLSM (Controlled Low Strength Material). It's essentially a lean grout that can be excavated, with some effort, if the need ever arises. It is self leveling so it will fill all voids.

  7. Back To Top    #7

    Join Date
    Jun 2010
    Location
    Toronto, Canada
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    Re: Gap under concrete border/deck

    Thanks everybody for the ideas. I'm going to look a bit more into mudjacking to see what this might cost versus a DIY approach.

    Quote Originally Posted by BigEinAZ View Post
    Is that a gunite pool or liner? If it is gunite, you could pour CLSM (Controlled Low Strength Material). It's essentially a lean grout that can be excavated, with some effort, if the need ever arises. It is self leveling so it will fill all voids.
    Hi BigEinAZ, I'm not sure what a gunite pool is, but we definitely have a liner over the underneath structure which I just assumed was concrete.
    20,000 Gallons Inground Vinyl Pool, 1 skimmer, 1 floor drain, 4 return jets, 1 vacuum intake
    Hayward Vari-Flo XL sand filter (SM2506T), Hayward EZ Flow Pump (SP-3107X10), Emerson Pump Motor (EB228), Hayward Comfortzone NG Heater, Hayward Chlorinator (CL220)

  8. Back To Top    #8
    Pool Tool's Avatar
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    May 2014
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    Western Chicago Area, IL
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    754

    Re: Gap under concrete border/deck

    The CLSM, aka flowable fill, would be fine to use for a liner pool as well. It is a very wet mix and flows almost like water. It will fill all the voids and dry with little to no shrinkage. Typical concrete withstands around 3000 psi of force whereas most CLSM target ~100-150 psi yield strength meaning it can be removed "easily" if you ever have to remove it unlike typical concrete.
    16' x 32' (21100 gal), vinyl, 1.5 hp Hayward SuperPump,
    Tagelus TA60/60D Sand Filter, Raypak 399K Digital Heater, TF-100

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