I would like to build a plywood hot tub.

Discussion in 'Boat Design' started by sprit, Sep 26, 2014.

  1. sprit
    Joined: Jul 2013
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    Location: Lexington, MA, USA

    sprit Junior Member

    I have had this post on the Wooden Boat Forum, with modest input. Perhaps there are others who would like to comment.

    It seems to me that our expertise with marine plywood should make it easy to design and build a simple backyard 2-4 person hot tub out of top quality marine plywood. My brief searches on Google for a suitable plan has not been very productive, so I decided to ask us… the pros who love playing with wood and glass and shapes and glue.

    Square plans would seem to have some advantages for seats in the corners, but circle plans would be stronger.

    Can epoxy stand the heat? Or is resorcinol necessary?

    Has anybody done this who is happy with the result?

    I am NOT interested yet in how to heat the water. I am NOT interested in a plastic tub. I don't want to use redwood etc.
     
  2. rasorinc
    Joined: Nov 2007
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    rasorinc Senior Member

    Heat will not be a problem unless you want to boil yourself. You will need an outside frame around it, a rather stiff one, so the weight of the water will not push the plywood out.
    You will need a ton of epoxy as you normally do not drain a hot tub at least 5 coatings, not thinned, on the inside and 3 on the outside for spillage. The more the better. I would also use a 7oz layer of glass finished Bright. Good luck............................
     
  3. Petros
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    Petros Senior Member

    it might actually be kind of fun to make it like a old carvel planked (plank on frame) boat hull, but "inside out"; frames on the outside, planks on the inside. Caulk the joints, use bronze screws and typical boat carpentry details, bronze plumbing, and it might actually be attractive and a fun piece for your deck.
     
  4. rwatson
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    rwatson Senior Member

    The appearance of the ply will not be fantastic unless you use very expensive clear epoxies and lightweight cloth.

    have you done the costings on plain Gelcoat on Polyester resin ?


    If you go square, save yourself a lot of finishing work and pre-epoxy the flat panels before you assemble them.
     
  5. gonzo
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    gonzo Senior Member

    All you need is to build a box and caulk the corners. Any polysulfide will do a good job. You can frame it with 2X4s and fill the gaps with styrofoam. There is no need for epoxy or other sealers if you are using boil tested marine plywood. If you want something better looking, then build it with cedar boards like a cask. They are not caulked but tight fitted and held together with hoops.
     
  6. fredrosse
    Joined: Jan 2005
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    fredrosse USACE Steam

    Plywood Hot Tub

    One day out on the lake the heavens opened up, and rain began falling at an amazing rate, soon the boat had about 6 inches of water in the bilge of this flat bottomed boat. Had no bilge pump at the time, just a scoop made from a plastic milk carton to get water out of the boat.

    My steamer is built of 1/2 inch and 5/8 inch marine plywood, covered with epoxy and fiberglass cloth. Steam exhaust piping, without insulation, is routed below the floors.

    The water got hot with the steam pipes submerged, soon to hot for comfort on the toes. No harm done, epoxy with fiberglass covering had no problems.
     
  7. philSweet
    Joined: May 2008
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    philSweet Senior Member

    Have you ever been responsible for maintaining a hot tub? You need materials that are compatible and understood so that the chemistry can be maintained correctly. That is the primary requirement. That is why plastered gunite, tile, and gel-coated fiberglass are so popular. Redwood or cedar work fine if you have a large hotspring nearby to feed the thing (no chemicals). Get a job at a pool company for a year and you will realize why this is a way to build a really hard to maintain hot tub. The purchase (or construction cost) is nothing compared to the operating cost of these things.

    I'd rather build a plyboat. The boat is cheaper to run, easier to clean, and has better resale value. There aren't too many objects which you can say that about, but a hot tub is one of them.
     

  8. SamSam
    Joined: Feb 2005
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    SamSam Senior Member

    I made one 4' square and 4' high using 3/4" cdx plywood, it sat outside in the open on a small deck. I had a 2x4 band around the top and bottom, the outside was painted with house paint. All the inside corners, the sides and the bottom, had triangular strips of wood to make it easier to fiberglass and clean. I used polyester resin, 1 or 2 layers (I don't remember) of 1-1/2 oz mat and gelcoat.

    There was a valve drain in the side at the bottom and a high inlet and low outlet fittings. The heater was wood fired, an old water heater tank with a 50' coil of copper tube inside, no pumps or anything, it just ran on convection.

    2 people were enough for that one, I also had another one I built in the traditional way with redwood. That was round with a 5' diameter and 3 or 4 could fit in that. I heated that the same way.
     
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