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Thread: Thickness of Shotcrete and Rebar Size and Placement

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    Join Date
    Aug 2014

    Thickness of Shotcrete and Rebar Size and Placement

    I am trying to understand how the pool shell should be constructed and have a few questions.

    Can someone tell me how thick the shotcrete should be in the floor, walls, and corners?
    What size rebar should be used? 3/8" vs. 1/2"
    What does #3 bar bond, #4 bar bond, and #5 bar bond mean?
    What should the placement be? Based on my reading here, it caries from 6" on center to 12" on center? But, what is the best placement?
    Should there always be gravel between the shotcrete and the ground?
    Should I get a soil analysis done? Is this necessary?
    Should I engage an engineer to draw the pool specs? Or can I rely on the PB?

    I know a lot of the answer to my questions depend upon my location, I live AZ.

    If anyone is from AZ, can you recommend a reliable pool builder? I have interviewed 4 and I have eliminated 2 and have reservations about the other 2.

    Thanks in advance!

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    JasonLion's Avatar
    Join Date
    May 2007
    Silver Spring, MD

    Re: Thickness of Shotcrete and Rebar Size and Placement

    All of these things vary with the pool size, shape, and the local soil conditions. Normally these details are determined by an engineer.

    Typically, if you are hiring a pool builder they take care of these details for you. You would normally only get involved at this level of detail if you are going to be your own general contractor for the build.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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  3. Back To Top    #3

    Join Date
    Aug 2014

    Re: Thickness of Shotcrete and Rebar Size and Placement

    Number 3 rebar is 3/8 thick and number 4 is 4/8 thick. The difference in cost for twenty feet of rebar is about a dollar or so. But the difference in quality is significant. Some builders use number three and some use number four and some that use number three beef up the steel in certain places with number four. If I had to do it again I would have aid extra for number four everywhere because the difference in cost is not too significant and in my experience (albeit quite limited) builders are sloppy and I'd rather they be sloppy with number four rebar since I will have much more support with it. Some builders will use number four n the bond beam and some will use number three but have extra pieces. I would insist on number four for the bond beam. As far as twelve by twelve or twelve by six the more steel the better and the difference on cost between twelve by twelve and six by twelve is not too significant. If you go to a Home Depot the price for twenty feet of number four rebar may be eight dollars or so (doing this from memory) so you can do the math to figure out the extra cost of extra steel. Typically the builders will have more steel in the deepend where they need more structural integrity. I think gravel is a good idea for drainage and the rocks they put down are very cheap so I would recommend them. In the Floor of the pool they typically want three inches of gunite below the steel and three inches above it. The walls are probably the same but not sure. In Cretan places like bond beam th may do twelve inches. When you price out the job you should ask how much steel is being used and out their answers in your contact.
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    Divin Dave's Avatar
    Join Date
    Oct 2013
    Longview, Texas

    Re: Thickness of Shotcrete and Rebar Size and Placement

    Hi Wanttoswim,

    The swimming pool is designed to withstand the forces exerted on the walls and floor by the water which will be in the pool. So the questions you ask are not straight forward. There are many factors to consider in determining how the wall should be built in order to support the load placed on it.

    The size of the rebar, the slump of the concrete, the location of the rebar, the spacing of the rebar the size and grade of the reabar are placed in the pool so it is structurally sound. So it's entirely possible, and even likely, that any given pool will have an assortment of rebar at different spacings. Water exerts a known amount of pressure upon a pool structure and the structure will be desinged to withstand that force.

    This is why concrete/ gunite pools are typically designed by an engineer and must meet the structural building codes of your municipality. Also, ANSI has minimum standards that a gunite pool should be contructed to.

    After the building plans have been drawn and have all sorts of specifications and info included... it's reviewed by an engineer in the building permit department, a building permit is issued if it meets the building code for structural, hydraulic and electrics. The building code guy is there to protect you, and as much of a PITA they can sometimes be, they generally do a good job of protecting us from ourselves as well as keeping our towns and neighborhoods safe from things that could make our lives miserable in the long run.

    There are several inspectoins performed during construction, and checking the rebar before the gunite is applied is one of those inspections. Its always good idea, if are there during the inspections in case you have any observations, concerns, or questions. The inspector should be able to ease your mind about them.

    Now having said all of this, generally speaking, concrete walls are about 8 inches thick and the floor is 6 inches thick. This assuming the soil it's being built on is stabile and not located in an earthquake zone.

    If I can offer a word of advice, try to refrain from requesting that x amount of rebar of your choosing be spaced at y distance. You will only alienate both the PB and Engineer with frivilous requests.

    If you want to know what the specs of the plans are, ask for a copy of the drawings and discuss them with the PB or the engineer. However if you disagree with the drawing, then you should proably be ready to scientifically / mathematically state your case about why you disagree and which building standard or municipal building code section your objection is covered under.

    As the pool owner, I would recommend that YOU make sure the pool is built according to the building plans or drawings and if you find a mistake during construction process, then bring that up with the PB as soon as you find it. Chances are 99% that your PB will not be there 100% of the time to check the quality of the workers, and workers are famous for making mistakes or for thinking that you really dont need what is on the plan.

    To find out about your soil, you can certainly have a geo-survey done at additional expense
    In many parts of the country, we already know if our soil is clay, loam, sand, rock, or whatever the case is, and generally how stabil it is, and what the water table is. People in the business usually skip a geo-survey and just go ahead and design the pool based upon geographiacally known conditions and a knowledge base of experience from prior projects.

    I hope this helps...
    Divin Dave,
    IG Vinyl, 15' x 30', 3 1/2' - 6' deep, Oval, ~15K gal, Intelliclor IC40, Intelliflo VS pump, Clean and Clear 420 Filter, auto-fill-disabled, Retrofit LED Color Light, Dolphin Nautilus Robot, TF100 Test Kit, Taylor K1766 Salt Test Kit, Tftestkit Pressure Gauge. Experience- it's what's learned just after you needed it most !!

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    Re: Thickness of Shotcrete and Rebar Size and Placement

    Without getting into specifics, there is usually a range of specifications for things like rebar size, concrete thickness, concrete strength, etc. At the lower end, the idea is to save money on construction. In my opinion, it's usually worthwhile to go above the minimum to help minimize long term problems.

    I would suggest that you inquire about the range of specifications, the cost differences, and the strength differences so that you can make an informed decision.

    Investing in better quality now can save you money and stress in the long run.

  6. Back To Top    #6

    Join Date
    Oct 2014

    Re: Thickness of Shotcrete and Rebar Size and Placement

    Re: Should there always be gravel between the shotcrete and the ground?

    Highly recommend the use of gravel below the pool, as this will provide a path for ground water to pass, and during construction will help keep the rebar from getting covered in mud in the event it rains before the shotcrete or gunite is applied.

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