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Thread: Build concrete inside fiberglass

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    Build concrete inside fiberglass

    Does anyone have experience with building a concrete pool inside a fiberglass in-ground pool? I'd like to hear stories, good and bad, and what to do or what to avoid.

    TIA
    Dave

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    Re: Build concrete inside fiberglass

    Quote Originally Posted by soflada
    Does anyone have experience with building a concrete pool inside a fiberglass in-ground pool? I'd like to hear stories, good and bad, and what to do or what to avoid.

    TIA
    Dave
    Why would you do this? If the fiberglass pool is so trashed, rip it out and do a proper pool.
    And, no, I've never heard of such a thing.
    In the industry, CSP (Certified Service Professional) by the NSPI and it's successor the APSP. My company services over 600 pools every year. I think the practices regularly espoused on this forum (especially the BBB method) are outstanding; however my comments will be often oriented towards the goal of getting it done, and getting it done right now!

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    Re: Build concrete inside fiberglass

    Why would you do this? If the fiberglass pool is so trashed, rip it out and do a proper pool.
    And, no, I've never heard of such a thing.[/quote]

    Why? Because there is a humongous screen enclosure around it and the deconstruction costs would escalate total cost beyond belief. Additionally, the space between houses and plantings would not permit excavation equipment to access the pool area. All digging/plumbing excavation will have to be done by hand.

    Now, do you have any sensible answers to what I thought was a reasonable question?

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    BobinBaltimore's Avatar
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    Re: Build concrete inside fiberglass

    Haven't read or heard of this being done. Part of the problem I can see is that fiberglass pools usually have a stone or sand layer under them which could cause settling/shifting problems with a concrete shell layered on. Also, as a matter of concrete curing and moisture dissipation, pouring a concrete shell in a fiberglass shell is kinda like pouring concrete into a plastic bag...it may not "breathe" properly. Another thought that comes to mind is that fiberglass can/does deteriorate in the ground over time, which might lead to some shifting or other pressures against in-ground pipes.

    I would think that the existing shell could be cut out without major equipment, perhaps being cut out much as you might remove a fiberglass shower enclosure. Big job, though. Assuming the shape and depth are acceptable, perhaps the prior excavation can be used as-is. Gunite can be pumped in from trucks in the front without removing the enclosure. As to whether piping could be reused (so as to avoid more excavation around the pool) I would assume it just all depends (age, location of returns, skimmers, condition, size, etc).

    All that said, I'm not a pro, and it sounds like an awful lot of work (cost) and risk. So I would step carefully in any direction taken.
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    Re: Build concrete inside fiberglass

    Quote Originally Posted by soflada
    Why? Because there is a humongous screen enclosure around it and the deconstruction costs would escalate total cost beyond belief. Additionally, the space between houses and plantings would not permit excavation equipment to access the pool area. All digging/plumbing excavation will have to be done by hand.

    Now, do you have any sensible answers to what I thought was a reasonable question?
    That would have been nice to know in the beginning.

    I think Qwax's response was perfectly reasonable given the original question. Building a concrete pool inside a fiberglass one is fraught with all sorts of issues.
    Dave J. TFP Moderator
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    Re: Build concrete inside fiberglass

    I would check into having the fiberglass pool reconditioned. I suspect this is quite possible as well as much cheaper, but I'm no expert. I have seen several youtube videos demonstrating this process. Good luck, and I hope you find a way to achieve your desired results in the most economic fashion.
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    Re: Build concrete inside fiberglass

    Quote Originally Posted by Bama Rambler
    Quote Originally Posted by soflada
    Why? Because there is a humongous screen enclosure around it and the deconstruction costs would escalate total cost beyond belief. Additionally, the space between houses and plantings would not permit excavation equipment to access the pool area. All digging/plumbing excavation will have to be done by hand.

    Now, do you have any sensible answers to what I thought was a reasonable question?
    That would have been nice to know in the beginning.

    I think Qwax's response was perfectly reasonable given the original question. Building a concrete pool inside a fiberglass one is fraught with all sorts of issues.
    I don't make a habit of posting on any forum without having a good reason and I expect responders to think in the same vein. I certainly would not have posted my query just for the heck of it! The response should have started from that point.

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    Re: Build concrete inside fiberglass

    I don't know if I'm right, but my gut tells me that building inside the old pool would be risky. The shell could flex or crack after the new concrete was poured leading to cracked concrete.

    Honestly, one option might be to see if the surface could be made safe for a liner. The bottom and sides could be lined with foam or otherwise treated to prevent liner damage.



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    Mod Squad Bama Rambler's Avatar
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    Re: Build concrete inside fiberglass

    And just how are responders to know that you have an access issue unless you let them know from the beginning?

    Nobody ever said that you didnt' have a good reason, but when you post an out of the ordinary question you have to let people know the extenuating circumstances. Of course in your case the correct answer is the same, rip the old one out and put a new one in or have the old one reconditioned.

    I'm not sure why you have an attitude about Qwax's answer or my response, unless it's simply not what you wanted to hear.
    Dave J. TFP Moderator
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    Re: Build concrete inside fiberglass

    Quote Originally Posted by soflada
    Why? Because there is a humongous screen enclosure around it and the deconstruction costs would escalate total cost beyond belief. Additionally, the space between houses and plantings would not permit excavation equipment to access the pool area.
    Unless you want to save the shell intact for some reason, from what I've been told, the easiest / most cost-effective way to remove (regardless of whether or not it's surrounded by an enclosure) it is to cut it up in place and remove it piece by piece. A sawzall might work, but one of the folks I talked to uses (if I understood him correctly) one of those gas-powered concrete saws, which you can rent.

    --Michael
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    Re: Build concrete inside fiberglass

    Quote Originally Posted by soflada
    Quote Originally Posted by Bama Rambler
    Quote Originally Posted by soflada
    Why? Because there is a humongous screen enclosure around it and the deconstruction costs would escalate total cost beyond belief. Additionally, the space between houses and plantings would not permit excavation equipment to access the pool area. All digging/plumbing excavation will have to be done by hand.

    Now, do you have any sensible answers to what I thought was a reasonable question?
    That would have been nice to know in the beginning.

    I think Qwax's response was perfectly reasonable given the original question. Building a concrete pool inside a fiberglass one is fraught with all sorts of issues.
    I don't make a habit of posting on any forum without having a good reason and I expect responders to think in the same vein. I certainly would not have posted my query just for the heck of it! The response should have started from that point.
    You left out some pretty important details in your original post which on it's own was an unusual question. Quite frankly after you described the "why" I'm sure more folks would be willing to brainstorm with you to find a solution to your problem. Asking for and sharing stories would be nice but putting a concrete pool inside a fibergalss pool, if it has been done is rare and not recommended nor something I would consider "sensible" without knowing more of the background.

    Along with great Q&A there have been many questions asked on this forum that not only end up being a bad idea but even potentially dangerous so the last thing you should expect is that we assume what your exact issue is and perhaps better explain what your good reason is so that members can better help you. Quax had no way of knowing you had access issues in your OP. Without his reply asking you to clarify "why" you likely would not have received many replies other than other members asking you to explain why.

    Now we have many members both in the Pool Building industry and DIY type folks. Knowing even more info could help them guide you further to find the most sensible solution such as your overall budget, the cost you were quoted to have the enclosure removed and re-installed, perhaps a picture or two of the current set-up, exact setback and access measurments (even if restricted) and just in general what you are trying to acheive.
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    Re: Build concrete inside fiberglass

    I'm sure the fiberglass pool could be resurfaced cheaper than building a new one inside of it. The liner suggestion is also a good one but I don't know the actual issues involved. Would need to hire someone who replaces liners to look at it for feasibility.
    The other suggestion would be to sawzall the old pool out and then just use the existing excavation and build a gunite or liner pool in it. Wouldn't need access for that but that is the most pricey and labor involved way.

    What exactly is wrong with the existing shell? Do you have pictures?
    Blaine

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    Re: Build concrete inside fiberglass

    Thanks for some good suggestions that will require further research and thought. Most critically are several comments about how well new construction inside the existing liner will both cure and live over longer periods of time. We are working with a long standing, reputable PB on this project and I have already forwarded several ideas for consideration.

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    UnderWaterVanya's Avatar
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    Re: Build concrete inside fiberglass

    Quote Originally Posted by soflada
    Thanks for some good suggestions that will require further research and thought. Most critically are several comments about how well new construction inside the existing liner will both cure and live over longer periods of time. We are working with a long standing, reputable PB on this project and I have already forwarded several ideas for consideration.

    As for curing - I wonder if they could drill holes in the existing shell to help with that aspect. People build concrete pools in clay soil which I don't think is a lot more pourous than fiberglass <LOL>, so the problem may be overstated. My real concern is that you cannot compact the soil and verify the state of the fill under the existing shell - so any shifting could compromise any type of pool surface at least potentially.

    What is the problem with the existing shell? Knowing this could help us understand how likley various options would be that have been discussed. Pictures wouldn't hurt either...
    Inlaws Pool Boy since June 14th 2012, Pool built ~ 2003, In-Ground, 16'x32'
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