hot-mop tar over plywood for budget houseboat hull construction?

Discussion in 'Materials' started by Squidly-Diddly, Feb 8, 2021.

  1. Squidly-Diddly
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    Squidly-Diddly Senior Member

    this is all about just pontoons, using plywood for skin of pontoons, and using hot tar to make watertight. don't really care about the deck, yet.
     
  2. kerosene
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    kerosene Senior Member

    it certainly sounds hacky. and 50' x 30' deck is not without cost and invested effort no matter how budget version it would be.

    that being said if the pontoons are removable and if there is enough safety margin that the setup stays afloat with 2 flooded in one end (or similar safety factor) then it might not end sadly. You might have to make better ones at some point in the future.

    would it cost that much to use polyester resin and fiberglass? and screws instead of nails.
     
  3. Barry
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    Barry Senior Member

  4. gonzo
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    gonzo Senior Member

    He keeps on coming with wacky ideas that are based on fantasy. Mr S-Q why don't you build at least one of your plans and show that it can be done?
     
  5. Rumars
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    Rumars Senior Member

    The hot tar will not work for long, it's not flexible enough. Some cold compounds can be used with felt in double planking, Buehler fans have done that. At the end of the day, it's hard to save money with this materials, the economy is just not there in today's market.

    If you want cheap pontoons that are "forever", do them in ferrocement. To be safe calculate them to accommodate the inevitable added weight from amateur manufacturing. If everything goes perfect and they come out to light you can always add ballast (rocks are cheap enough).
    Otherwise just use polyester and fiberglass over a cheap mold (cardboard cylinders work well for this).
     
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  6. gonzo
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    gonzo Senior Member

    If all you need is a cheap barge, used utility poles are probably one of the best options.
     
  7. Squidly-Diddly
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    Squidly-Diddly Senior Member

    You think it will soon develop cracks due to being too brittle if applied hot to inside and out of plywood and 2x4 nailed box and placed in water? I'm thinking it might need to be fairly thin coat more like paint to prevent alligatoring, similar to how thin bead of caulk in a joint can stretch but a thicker that 1:1 will tend to break off from one surface. You think it will de-lam? A buddy was building and renting duck blind boxes made out of plywood, 2x4 and standard not for used under water Construction Adhesive and some "water proof paint" and these were sunk into swamp water about 1-3ft deep and stuck to the mud bottom and lasted for years.

    Reason I was thinking of tar and plywood besides low2no cost materials is instant waterproofing/gluing of hot tar for not just construction but any mods or repairs, VS something like cement where not only do you need to know what you are doing but its going to be a few weeks before it can go in the water, and its heavy. A tarred plywood box 24x4x4ft should still be light enough to be manhandled by a few strong guys and transported and launched easy. Maybe a couple 4x4" skids to protect the bottom and maybe even some cheap plastic wheels on 1/2" simple axles through the 4x4s.

    But "no flexible enough" is a concern so I'm wondering if stuff can be added to hot tar that will make it stay more flexible when cooled. Might be as easy as dumping some dirty motor oil or lighter tar into the mix. Also still wondering if tarred floats would be a big environmental violation.
     
  8. gonzo
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    gonzo Senior Member

    Can you post a source of your claimed "no-cost" materials? :rolleyes:
     
  9. Rumars
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    Rumars Senior Member

    It's all a tradeoff, to thin and it won't waterproof, to thick and it will crack in service, to flexible and it will soften and run in the summer heat. Any hard corner like a frame to skin intersection will be a liability. Trying to adjust properties by mixing in things is a job in itself, you can just forget about it. I would use hot tar only if there was no other option.
    The only marine formulation for a hot tar product is Jeffries marine glue, used to pay the seams in traditional decks.

    Low cost is relative, for the 200$ a pro charges to hot mop, one can buy enough budget epoxy and glass to do the job.
    With ply, surface protection is secondary, edge protection is paramount. Tape the edges, bog and tape over all fasteners, paint the faces and it's good. Maybe use some wood preservative on the panels before painting.
     
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  10. gonzo
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    gonzo Senior Member

    I used tar products in the past to fi leaks in a plywood dinghy. The repairs would last a few days until water got behind the tar and leaks started again.
     
  11. bajansailor
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    bajansailor Marine Surveyor

    Squidly, I think the general consensus here is that flinging tar at your new house boat is most definitely not a very good idea - there are many better ways of keeping the water out of your houseboat, and protecting it.
     
  12. KeithO
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    KeithO Senior Member

    Who would even allow a tar covered behemoth to be launched in California nowadays ? Its only a couple of steps removed from launching an oil slick... Tar is a pretty toxic material.
     
  13. gonzo
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    gonzo Senior Member

    Tar is elastic as long as the oil content doesn't leach out. It is like asphalt. You can observe an old asphalt road after some time when it get grey, dry and starts cracking and crumbling.
     
  14. Squidly-Diddly
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    Squidly-Diddly Senior Member

    thats a big question. I've seen fairly recent tar coated telephone pole sized pilings sunk into water, and AFAIK hot tar is still in common use for roofs and still used on roads.

    Just like you can do ANYTHING if you call it an "emergency repair" and Build Dept is kept at bay (only wealthy people seem to do this or be able to), maybe I could call it "just a big patch" when the whole thing is covered with tar.

    I guess I'll just have to make a test box about 2'x2'x4' tall and coat with tar then set out in some willows with some ballast.
     

  15. gonzo
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    gonzo Senior Member

    Utililty poles are coated with creosote not tar.
    Roads are paved with asphalt not tar.
     
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