Glassing fir to prevent checking

Discussion in 'Materials' started by jbo_c, Apr 19, 2020.

  1. jbo_c
    Joined: Jul 2017
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    Location: Gainesville, GA

    jbo_c Junior Member

    What’s the consensus here on weight of glass to prevent fir from checking? I’ve read anything from 2oz to 6oz. 2oz seems pretty light, but is 6oz really necessary? Hate to put 6 if 2 will do it, but I don’t want to find out 2 was really too light one day down the road. Just go with 6oz?

    And just to confirm, this is plain woven cloth, not twill or something else, right?

    Jbo
     
  2. bajansailor
    Joined: Oct 2007
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    Location: Barbados

    bajansailor Marine Surveyor

    Will you be using epoxy or polyester resin?
    I think that it will depend a lot on the thickness of the fir that you want to coat in fibreglass (I presume that this is what you want to do?).
     
  3. jbo_c
    Joined: Jul 2017
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    Location: Gainesville, GA

    jbo_c Junior Member

    Only epoxy for me.

    Why would the ply thickness matter? Isn’t checking just on the surface? To answer the question, it will be 1/2” and 3/4” AB marine fir.

    Thanks.

    Jbo
     
  4. bajansailor
    Joined: Oct 2007
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    Location: Barbados

    bajansailor Marine Surveyor

    My apologies, I thought you were going to glass solid timber planks, rather than plywood, hence the question.

    Are you laying a fir plywood deck, or will this glass be on the hull?
     
  5. jbo_c
    Joined: Jul 2017
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    Location: Gainesville, GA

    jbo_c Junior Member

    At least a deck for the time being, but I own the wood and I’m getting the itch, so sooner or later some will likely become a hull. :)

    Though I guess on the hull is moot on the outside at least, since it will probably sport some biax cloth anyway.

    Jbo
     
  6. kapnD
    Joined: Jan 2003
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    Location: hawaii, usa

    kapnD Senior Member

    If you’re using it as a deck, I’d tend towards heavier glass, for protection.
    2 oz will be eggshell thin, very susceptible to damage, 6 oz proportionately better, but IMO, still not enough protection for a deck.
    Proper priming and painting should be enough to just prevent checking, if the lumber is dry.
    Of course, this all depends on variables not stated here.
    Are we talking about a flyweight racing boat, or a commercial trawler?

    “I’m getting the itch”, LOL, that will come soon after the resin hardens!
     
  7. jbo_c
    Joined: Jul 2017
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    Location: Gainesville, GA

    jbo_c Junior Member

    Definitely not building a flyweight boat with fir. Just replacing a deck on a bass boat right now, but will be building a small “trawler” of sorts soon enough.

    Yes, ‘the itch’ manifests itself in different ways at different times.

    Jbo
     

  8. BlueBell
    Joined: May 2017
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    Location: Victoria BC Canada

    BlueBell Ahhhhh...

    Title of thread, no mention of plywood.
    From OP
    Second post first mention of ply...

    2 oz would suffice to stop checking.
     
    Last edited: Apr 19, 2020
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