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Thread: Base and Backfill material for fiberglass installation

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    Base and Backfill material for fiberglass installation

    Hi all, Looking for some thoughts on base and backfill materials, specifically for a fiberglass installation. I have done lots of research and spoken with many experts (local and online) on the benefits and challenges of sand, gravel, round stone or pea stone, and even flowable fill.

    Sand - seems to be the old standard, and while soft, and easy to grade for a base, it allows for settling and even wall bulging (especially when wet). I know many people talk about being able to 'wash' the sand into voids, but my research also indicates that this is not as effective as many installers and manufacturers will lead you to believe. I'm inclined to think that this may still be one of the best materials for base material (so long as water does not get under the pool shell and the base was prepared perfectly).

    Gravel - 3/4" minus washed stone seems to be very solid, allows for water to pass through, naturally compacts when placed (upwards of 90%, I believe), and does not have the same challenges as sand. That said, even though the pieces are small and should not cause damage to a fiberglass shell, and some reputable installers will swear that there is not chance for damage, they are still angular and sharp in nature, causing potential for damage.

    Round Pea Stone - My understanding is that this has many of the benefits of gravel, but without the sharp edges, thereby removing the potentially hazzardous sharp edges. Supporters will say that makes this a better medium than gravel, but others have said the stone's round nature act like ball bearings against each other and cause slippage and settling.

    Flowable fill - I'm still learning of the properties of this material, however, it sounds as though it's extremely sturdy and easier to fill into difficult areas (without leaving voids or falling back), such as under stairs and swimouts. I know that most FG manufacturers reinforce these areas of their shells, but also that these areas are difficult to back fill and are prone to cracks if not backfilled properly.

    Based on the below info, wondering if the best approach is a sand base with round peastone side fill and flowable fill underneath stairs and swimouts. Thoughts? Thanks.
    10k gallon fiberglass freeform pool, Paramount SwingJet system, Dolphin DX5 robot, Pentair 48" Tagelus sand filter with glass media, WhisperFlo 1 HP pump, Hayward H200FDN natural gas heater, TF-100 Test Kit, and, of course, Margaritaville Tahiti blender!

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    CUTiger78's Avatar
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    May 2009
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    NoVA
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    Re: Base and Backfill material for fiberglass installation

    You might want to PM member MCaswell and see if he has any insight. He had an interesting fiberglass pool thread at http://www.troublefreepool.com/threads/41555-New-fiberglass-pool-is-full-of-cracks-HELP!.

    ​Good luck!
    36K gallon 42X22 gunite/plaster kidney-shaped IG;
    1 hp Hayward Super Pump (new in 2012);
    Hayward S244T sand filter w/ Zeosand (both new in 2009);
    175K BTU LAARS Lite2 LG natural gas heater; Polaris 380;
    TF-100 test kit.

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    Re: Base and Backfill material for fiberglass installation

    Hi. Thanks. We have had some PMs in the past, thanks!
    10k gallon fiberglass freeform pool, Paramount SwingJet system, Dolphin DX5 robot, Pentair 48" Tagelus sand filter with glass media, WhisperFlo 1 HP pump, Hayward H200FDN natural gas heater, TF-100 Test Kit, and, of course, Margaritaville Tahiti blender!

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    Join Date
    Sep 2009
    Location
    Frederick County, MD
    Posts
    175

    Re: Base and Backfill material for fiberglass installation

    I am a believer in gravel. My PB has used gravel for over approximately 400 pools.

    While you can use anything, the compact-ability of gravel is far superior to the issues with sand and pea gravel. I have not seen flowable fill used as back-fill material so I cannot comment on that.
    Jim

    Southern Frederick County, MD - Leisure Moroccan 38 Fiberglass Pool - 19,800 gallons
    Pentair 1.5 hp 2 speed pump - Cartridge filter - Dolphin robot - TF-100 Test Kit - SWCG

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    Re: Base and Backfill material for fiberglass installation

    Hi Winger 03, thanks for the reply. Pretty sure I know who your PB is based on location and # of pools you mentioned. I have had emails with them, and they have been very helpful. I like their approach as they appear to be focussed on quality and getting the job done right. I agree on the compactibility factor and therefore, have been considering gravel for the side backfill, but still with compacted sand as the base due to the no sharp nature. The flowable fill stuff seems to be a great product and was recommended for under those pressure point areas. Appreciate the reply!
    10k gallon fiberglass freeform pool, Paramount SwingJet system, Dolphin DX5 robot, Pentair 48" Tagelus sand filter with glass media, WhisperFlo 1 HP pump, Hayward H200FDN natural gas heater, TF-100 Test Kit, and, of course, Margaritaville Tahiti blender!

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