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Thread: Hard bottom vs. soft bottom on wetlands

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    Hard bottom vs. soft bottom on wetlands

    I'm in the process of contracting a PB and working out the details for the pool configuration. It will be a vinyl w\steel wall 15 x 27' kidney (12k gallons) ranging from 3.5' to 6.5' deep. I live near the water on Long Island. I recently had a test hole dug on my property and found that the water table fluctuates between 4.5' to 6' below my yard surface depending on the tide. Most of the material that was found was sand, but there was some bog at the 6' level. The price for dewatering is 3k which includes the dewatering process and a hard bottom consisting of concrete mixed with sand and the installation of a dewatering pipe which can be used for future dewatering when it is time to change the liner. I complained to the PB about the price of dewatering and he said I could save money if I don't go with the hard bottom, which would mean using a sand bottom that comes with the standard pool package. Does anyone know what the pros and cons are of this scenario? I have a feeling the PB might be trying to make the deal seem more attractive, but I would prefer to spend the extra on the hard bottom if it will help me in the long run.
    12.5k Doughboy, 24'x16'x52" Oval, 6' Deep End, Semi-IG, Vinyl, Sand, Waterway 1.5 HP 2 speed. Power Ionizer, Full Sun

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    Re: Hard bottom vs. soft bottom on wetlands

    I don't think I understand the advantage of a hard bottom. It seems to me the liner may float if the table comes up high enough regardless of the type bottom. What does the hard bottom do to prevent that?
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    Re: Hard bottom vs. soft bottom on wetlands

    From what the PB explained, if you have lot of bog it could be an unsuitable foundation for a pool bottom. The hard bottom would help provide support. There are tons of pools in my area and I'm not aware of any issues with liners floating from the water table. This isn't to say it cant or hasn't happened, but the PB did not mention that it would be a problem.
    12.5k Doughboy, 24'x16'x52" Oval, 6' Deep End, Semi-IG, Vinyl, Sand, Waterway 1.5 HP 2 speed. Power Ionizer, Full Sun

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    Re: Hard bottom vs. soft bottom on wetlands

    It would seem that there are two separate issues here that the PB is bundling under one heading.

    The first is that the high water table may cause the liner to float were you to empty the pool at some point in the future. This can be overcome with the dewatering and the dewatering pipe for future use and as Dave has stated is an issue independent of floor/pool type.

    The second is that the soil conditions at the bottom of the pool may not be suitable without further grading/support which I assume where the hard bottom comes in. My question would be if that were the case what would stop the hard bottom from moving? Has an engineer been involved in looking at the soil sample or was this just done by the builder?

    Both issues are related to water table and soil conditions but I would see them as separate issues.
    38'x24' freeform IG gunite, 26k gallons, 3.5' - 7'
    8t Moss rock waterfall with gunite slide
    SWCG, 2 x 2.7hp Hayward Tristar pumps, booster pump, 425 sqft cartridge, 400,000 BTU heater, Polaris Black Max 280, ProLogic PS8 & Aquapod

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    Re: Hard bottom vs. soft bottom on wetlands

    Well, you may have to get more from your PB. If the subsoil is unsuitable for a sand base, I would depend on his experience but I would learn more from him.

    The water table after construction (liner floating) is a seperate issue like cbink said, but I would get some reassurance you won't have issues. Wellpoints to lower the surrounding water table are easy now but very difficult after construction.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    Re: Hard bottom vs. soft bottom on wetlands

    I appreciate everyone's help with this. It sounds like I should press the PB for additional info. The company I'm dealing with has a good reputation and experience building pools in my area. The downside is I'm dealing with a sales rep that doesn't have the same experience as the engineer\construction lead so he may not be giving the best advice and answers.
    12.5k Doughboy, 24'x16'x52" Oval, 6' Deep End, Semi-IG, Vinyl, Sand, Waterway 1.5 HP 2 speed. Power Ionizer, Full Sun

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    Re: Hard bottom vs. soft bottom on wetlands

    if you go sand and the liner does float plan on the sand shifting and the floor needing retroweled. when I do liner repalcements I won't touch a sand floor, here in Cincinnati we use vermiculite/portland cement mix for our floors. I have seen a liner float and with a hard bottom you can pump the water from behind the liner and get it to go back in place. Go with the hard bottom!!!!

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