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Thread: What sort of pool for difficult soil types? SE Texas.

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    What sort of pool for difficult soil types? SE Texas.

    I'm looking for some ideas / views that I may not have considered for a new pool build south of Houston, TX. Sorry for the length, there are several questions in here; I'm finding conflicting data and would appreciate some independent expertise.

    I prefer the feel of a vinyl liner or tile to a plaster finish, and would prefer to avoid plaster if possible. I've looked at “smooth” plasters such as durazzo, but still prefer either vinyl or glazed tile. Is there another finish I should be looking at? I like fiberglass too, but I can't see how to make it work for us.

    Basically, we live in a swamp. Mostly gumbo soil (expansive), in a shallow depression, with significant groundwater drainage problems (minimal risk of flooding from waterways, but rain takes a LONG time to drain away, and the local water table can sit right at grade level for several days after a heavy rain).

    So, I'm worried about in-ground gunite & plaster or fiberglass pools floating, and about the pressure that the expansive soils can apply to pool walls.

    Is there a significant risk from the expansive soil on vinyl pool walls? The market around here is almost exclusively gunite, I suspect this may be related, but I can't get a definitive answer on why the market is that way. Aren't gunite walls also susceptible to expansive soils?

    One option we are considering to minimize the risk of the pool shell floating is to go with the pool sitting partially out of the ground, keeping the water level several inches above grade, but I'm still concerned that maintenance down the road is going to be nearly impossible if the groundwater is high. Is there anything I can do to mitigate the risk of a shell popping out?

    I have not found a fiberglass pool that can be left partially out of the ground, and I don't have enough space to slope the deck gradually up from current grade at the house several inches up to the pool edge.

    Is one construction method better than the others for this type of soil? How about blending techniques? I am willing to think outside the box if none of the "big 3" methods is suitable.

    I considered getting a gunite shell for strength, and lining it with vinyl for the feel, but there could be a problem with water getting behind the liner – already confirmed by web searches and posts on this website. Is there a way to avoid that? One solution I am contemplating is to utilize the main drain in the gunite shell as a drainage sink for water between the liner and shell. I don't want main drains in the pool anyway, I'm going to rely on skimmers and a vacuum. But if I got a gunite shell with main drains, is there anything I could put over the main drain to protect the liner while allowing water to drain away? Is this opening up a can of worms for mold growth?

    Are there other solutions?
    Houston, TX
    Designing pool for 2013.

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    duraleigh's Avatar
    Join Date
    Apr 2007
    Sebring, Florida

    Re: What sort of pool for difficult soil types? SE Texas.

    A liner pool has a common disadvantage in a high water table.......the liner will float. This can be corrected (usually) by establishing "wellpoints" or French Drains around the pool's perimeter so that the ground water is always at an acceptable level next to your pool.

    Secondly, both gunite and liners pools must be drained VERY cautiously in a high water area. The gunite can pop up and the liner walls can collapse.

    Fiberglass will be even more susceptible to popping up.

    My bet is there are some PB's there who know your local conditions and can handle vinyl construction if that's what you want.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    Join Date
    Apr 2012
    Klein Tejas

    Re: What sort of pool for difficult soil types? SE Texas.

    I don't think I would call our soils "difficult". Yes it's sand and expansive, impermeable clay with no natural rocks. It digs easily and it's composition known.
    Only some parts of town have high water table issues, primarily in the south and southwest parts of the city or if you are located near any bayous. Look at some of the builds on this sight and you'll water flooding the hole as they are digging it. That's a high water table.

    I know nothing about vinyl pools but it might be these unstable clays that prevent their use. I've never seen an inground vinyl pool in this area.

    I like the smooth finish also that's why I went traditional marcite plaster in my pool.

    edit to add: once the pool is filled with water it will resist the uplift forces from the hydrostatic forces. I've seen pools float out of the ground but only when they are drained for significant lengths of time.

    Duh, I reread your post only to see that you said you're south of the city. You might have your excavator bore some soil samples to determine if you have a water table issue or just trapped water. In an internet search I found this document on engineering pool shells in Houston
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    Re: What sort of pool for difficult soil types? SE Texas.

    I built a liner pool this year and ran into water at a bought 4 to 5 feet and pumped out 100 gal a minuet during the build. If you do a liner pool I would use composit walls and you need to have at least 2 feet of cement around pool to lock in the walls. I would also use stone backfill so if you pump down the water in the pool you can pump the water down around and under the pool first . Once water in pool is a little above ground water you can shut of your drain pump. Do you have someplace to run some drain pipeto. You could run some drain pipe around pool in the stone 1 or 2 feet down to a storm drain or ditch.

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