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Thread: Float Tank

  1. #1
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    Float Tank

    Hi All,
    I have no experience with fiberglass. I have been researching how to work with it. I am making a float tank. A float tank is for relaxation and meditation. It has 10 inches (25cm) of water heated to skin temperature 93.5 - 94.5 F (34.2 - 34.7 C) and 800 - 1000 lbs (363 - 454 kg) of epsom salt, so that floating is effortless. It's going to be 8' x 5' 6" x 7' high (2.4 m x 1.7 m x 2.1 m high). I'm planning to make a box by framing the walls, floor and roof with 2x6 (5x15 cm) lumber, attaching OSB (chipboard plywood) on the inside of the framing, applying mold release agent to the inside, and then fiberglassing the inside. I heard that fiberglass does not like 90 degree angles, it's weaker. Is that true? I ripped some 2x2 (5x5 cm) lumber diagonally that I will put in the corners so the corners will be a little rounded. Will that make the tank stronger? For the ceiling, can I apply resin overhead? Will the resin soak into the mat? Oh by the way I plan to use 2 layers of 1.5 oz chop strand mat (I'm not sure how to convert that to metric, but I think its equivalent to 450 gm csm) and isophthalic polyester resin. Will that be strong enough for me to take the mold off and move the empty tank without cracking or breaking it? I will need to have one hole in each end of the tank to add the plumbing for the filtration system. Is it better to perhaps cut the hole in my mold, apply release agent to the pvc pipe, and then cast the fiberglass around it, or just cut the hole through the fiberglass later? Can I use carnuba car wax as a release agent? If I put wax on the mold would that wax get into the resin and cause it to have a hard, non-tacky finish? I don't want that because I want to add a second layer of mat, and two coats of gelcoat. The final coat of gelcoat would have the wax additive. Are two coats of gelcoat sufficient?

    Thank you in advance for any answers to my questions and any advice. I'm sure I'll have more questions.
    Last edited by Darren; 13-11-2015 at 08:51. Reason: found the conversion for csm

  2. #2
    Super Moderator Alex's Avatar
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    Hmmm,

    I can tackle a few answers now but overall I am not sure you have quite grasped the engineering or perhaps I am not understanding this post correctly.

    >>attaching OSB (chipboard plywood) on the inside of the framing, applying mold release agent to the inside

    So you plan on making a mould. This is fine but OSB is probably the worst material you could use as a mould face. It is so rough and gelcoats/resins absolutely love to stick to it. You wont be able to use this as a mould surface without sealing it first with either plug facing paint or bonda surface sealer (3 coats) or 2 pack before suggesting a mould release agent could be used. I would probably use melamine board as the plastic coating doesn't require release agent and will leave a gelcoat with a sweet finish when released.
    You cannot mould sharp corners, you will get air bubbles where the mat will not conform and the gelcoat will chip. If you use wood fillets they will need to be sealed and treated like any wood. To be fair the fillets don't have to be big, normally plasticine is used to create these (with a ball ended tool) and the plasticine is removed once released from the mould.

    >>For the ceiling, can I apply resin overhead? Will the resin soak into the mat? Oh by the way I plan to use 2 layers of 1.5 oz chop strand mat (I'm not sure how to convert that to metric, but I think its equivalent to 450 gm csm) and isophthalic polyester resin. Will that be strong enough for me to take the mold off and move the empty tank without cracking or breaking it?


    It probably will be strong enough to remove but will be pretty wobbly. This will be about 2mm. If you filled that with water it would be about as rigid as a balloon. If you want a unit that is light and rigid you will need to use a core material like nidaplast
    of about 15mm. Your layup would be along the lines of :Gelcoat> 1 layer 1oz> (allow to cure) 1 layer 1.5oz with the nidaplast attached to this wet layer (then allow to cure)> then a 1.5oz liner all over the inside> topcoat (either premixed of gelcoat with wax) This will make the flat areas stiff and will have a massive sound deadening boost which I am sure will be welcome for this sort of thing.

    If I wanted a float tank, that's how I would make it. Check out the nidaplast link to see how it is fitted and it's benefits.

    Why are you fibreglassing upside down, I don't understand why you wouldn't make the lid separate and bond it on.

  3. #3
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    Thank you

    Hi Alex, thank you for your reply and your advice. You're absolutely right I don't quite grasp the engineering but I'm happy you do and you're willing and enabled to share. I've been looking for someone who can answer some of my questions.

    I'm not even familiar with the materials you mention. I will do some research and reread you post a few times.

    My reasoning for applying release agent to the OSB is so that I can move the tank. I was thinking that with the OSB and the framing it would literally weigh a ton and I am concerned that trying to move it would break it.

    Got to go ...

  4. #4
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    How would I

    Hi Alex,
    Am I correct that you said I would need to put fiberglass all over the outside and the inside of the box made of nidiplast? How would I bond the top?

  5. #5
    Super Moderator Alex's Avatar
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    Yes you would have to fibreglass both sides but the nidaplast weighs very little and for the same rigidity from an equal thickness of wood. So a panel would be as stiff as one with a wood core but without the weight of the wood!

    What do mean about bonding the top, it wouldn't be any more difficult, right?

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