Fibreglass sheet

Discussion in 'Materials' started by DTurnham, Aug 22, 2020.

  1. DTurnham
    Joined: Sep 2014
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    DTurnham Junior Member

    Hi all,
    I wonder if anybody can help me...
    I have been mulling over the idea of building a stitch and glue canoe. I have seen a simple design I like the look of and was pricing up materials...the epxoy system certainly seems to be the most expensive part of the build process.

    However, I have found a supplier who can produce 4mm fibreglass sheets (gelocoated) to the same size as a sheet of ply.

    Do you think it would be possible to use this in place of ply along with poly resin for stitch ang glue? I don't know whether the sheet would be flexible enough or whether the gelcoat would be likely to crack.
     
  2. Blueknarr
    Joined: Aug 2017
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    Blueknarr Senior Member

    Welcome to the club

    It depends on a few factors.

    What is the canoe's design?
    Are the panels made with epoxy or polyester?
    4 mm seems a bit thick and therefore heavy for my concept of a canoe.
     
  3. DTurnham
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    DTurnham Junior Member

    Thanks for the reply. I'm not sure of the resin used in the sheets, I only assumed it was polyester as I wasn't sure why they would use epoxy to layup sheets like this.
    The thickness was arbitrary, to be honest, They also do 2mm ones if that might wwork better.

    Also, I was wondering whether producing my own sheets form chopped strand and poly resin might work. Possible make the form using a modified stitch and glue method then fair with polyester based two part/gelcoat filler?
     
  4. fallguy
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    fallguy Senior Member

    The bond strengths of the thickened poly are not ideal, imo.

    If you were going to stitch n glue poly glass sheets, I'd at least step up the bonding to epoxy. Also need to be careful to prepare the substrate for mechanical key.

    But not a big fan of the idea vs marine plywood.

    I'd also start with a dev panel plan and not guess.
     
  5. KeithO
    Joined: Jul 2019
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    KeithO Senior Member

    You can buy fiberglass siding for RV's by the foot, its called Filon. It is CSM with polyester resin, no gellcoat. Costs $15/ft 8.5ft wide available in any length. Its about 0.043" thick. I dont think it is very strong given that it is CSM with poly.
     
  6. Blueknarr
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    Blueknarr Senior Member

    Making your own sheets certainly adds a new dimension to the project.
    It is doable. There's some advantage to making your own.
    However, without knowing the design of your canoe it is impossible to give advice as to the matrix of the proposed sheets
     
  7. Mr Efficiency
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    Mr Efficiency Senior Member

    The sheets are just too flexible to be used for that purpose. You can use sandwich laminated sheets and bend them, within limits.
     
  8. waikikin
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    waikikin Senior Member

    DT
    There's some merit in the system I think you'd be best off making your own to full length and then using a female set of forms/stations so the internal tabbing or additional layup can be uninterrupted- the hull/deck join often tricky on canoes as the fine ends hard to get into. If the deck is heavily cambered that might give it's own set of surface control issues until complete. I all you want is a fibreglass kayak these are pretty cheap secondhand so begs the question are you a paddler or a builder? The sheet system has been in use before in boat construction, even back in the eighties there was one called "blue sky" - might have been Prime composites but long ago now. Fibreglass canoes are great- I've got a Canadian style that lives on the roof of my station wagon- every now and then I need to add some glass to the bow where it skids on and off the launching ramp- a quick grind, splodge on some choppy and resin and ready to go... once it's set:)
    Jeff
     
  9. DTurnham
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    DTurnham Junior Member

    Thanks for all the replies. Seems like maybe, all things considered, using marine ply glassed with cloth woud be the best option. In terms of keeping costs to a minimum, would using epoxy for the joint filleting and poly for wetting out the cloth covering be an option?
    I realise that I could buy a second hand FB canoe, but firstly, I like the idea of the challenge and satisfaction of building my own and secondly, I'm in the UK and a decent second hand open canoe here is generally at least £700. I think I can build one cheaper than that if I'm careful...hence the questions on materials to reduce costs as much as is viable.
     
  10. Blueknarr
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    Blueknarr Senior Member

    Have you settled on a design yet?
    Most newbies don't realize the engineering requirements for changing boat building materials or methods.

    Polyester has less adhesion than epoxy. It will not adhere with sufficient strength to epoxy. So don't plan on using it to sheath over epoxy joints.

    Polyester has an earned reputation for inadequate adhesion to wood. Therefore epoxy is the recumended resin to use with wood.
     
  11. Mr Efficiency
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    Mr Efficiency Senior Member

    Whilst plenty have used polyester resin to sheath timber boats, it does have the dual issues of being much less adhesive, but also more permeable by water, the latter not that great a problem unless the boat always in the water. I wonder, and it could probably easily be tested, if using an initial coat of non-thixotropic polyester ( "normal" resin contains thickening agents to make laminating on vertical or overhead surfaces practicable) applied to the plywood, would give enhanced adhesion. If Ondarvr reads this, we may get the answer, but it is likely to be an answer qualified by the type of wood involved, and even within a timber species, there is doubtful homogeneity. I guess in the end, the much reduced physical properties of polyester compared to epoxy, also factors into the equation.
     
  12. Rumars
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    Rumars Senior Member

    Yes, you can use premade fiberglass sheets to make a boat, it has been done before. The problem with this approach are weight and stiffness, fiberglass is a lot heavier and much more limber then plywood. The design has to accommodate this factors, you can not exchange 4mm solid fiberglass for 4mm plywood, especially with a canoe designed for S&G that probably has no framing at all.

    If you are looking for cheap, build a strip plank boat. Spruce/pine/fir for the strips and 200gr/sqm fiberglass in epoxy inside and out, plus some paint. If you don't buy the wood per meter at the home improvement store and use the cheapest general purpose epoxy it should be cheaper then marine ply.

    If you want a cheap foam core that works with polyester use polyurethane foam.
     

  13. Blueknarr
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    Blueknarr Senior Member


    I believe that a significant portion of the failed polyester/wood bonding is due to the tendency of polyester users to have very poor craftsmanship. They either use a thinned "sealing" coat or directly laminate to dry wood.

    You hit the nail directly on the head as to the best way to laminate to wood regardless of type of resin being used. Start with an un-adulterated coat. Wait for it to gel but before fully curred to add FG cloth.
     
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