Fiberglassing plwood boat

Discussion in 'Wooden Boat Building and Restoration' started by Stavbergen, May 12, 2019.

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  1. Stavbergen
    Joined: Apr 2019
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    Stavbergen Junior Member

    Hi all, i was watching some youtube videos on restoring some old chris-crafts and they spoke about how woooden boats should never be fiberglassed because when water gets inside the hull it penetrates through the planks and gets to the fiberglass and has no where to go so just stays there and rots the wood. Which makes sense. Is this true? Also does this apply to plywood as well?
     
  2. Blueknarr
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    Blueknarr Senior Member

    Mostly sort of kind of true, but not always.

    I liken it to my law of fingers: for every rule of thumb there are at least four fingers of exception.

    Most techniques for sealing water out will be more effective sealing water in.

    Stich-n-glue plywood construction requires some fiberglassing. If it is done poorly then water can inter the plywood far faster than it can leave. Like a kitchen sponge soaks up water way faster than it dries out. If the fiberglassing is done correctly then there is little chance that water will enter until the glasswork is damaged. Often extra glass is applied over at risk areas.

    Glassed over wood boats need to be inspected frequently to ensure the wood is not compromised.
     
  3. missinginaction
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    missinginaction Senior Member

    You can search for threads on this subject for more information and there is a LOT of it on this site. Paul Ricelli (known as PAR) who passed away last year posted generously on this topic for years. I don't have time today to beat this subject to death but I will tell you this: Done properly, PROPERLY being the key, plywood and hardwoods can be sealed from water penetration using EPOXY resin and epoxy resin only. Epoxy's waterproofing properties have to do with the chemical interlinking of the cured resin matrix. Polyesters are not waterproof for similar reasons. Poly has it's uses to be sure but as a coating and waterproofing for wood it's no substitute for epoxy.
    Sealing plywood for instance requires a minimum of three coats of resin on all six sides of the piece. Every fastener that passes into or through the piece needs careful attention. Good bedding compounds, epoxy grommets (see photo - that's a sealed hole for a 1/4-20 machine screw in the side of my flybridge which is made of plywood with fiberglass sheathing) and even better, no fasteners at all. epoxy grommet.jpg

    The bottom line is that with proper encapsulation and coating you can achieve completely waterproof wood//fiberglass/epoxy composite assemblies that will provide many years of service. It's time consuming though and expensive. This is why just about all modern boats are made of fiberglass, composites or metals.

    I'm not qualified to comment on building strip plank hulls as I've only worked in ply or mahogany decks and boat cabins/flybridges. I believe though that those Chris Craft hulls were originally designed to be varnished and caulked. This allowed the wood to get wet, swell and seal itself. Using epoxy and trying to keep water out would be counter to the way the hull was designed to work.

    Search for posts by PAR and/or go to his website at paryachts.blogspot.com and read the sections on liquid joinery and epoxy tips and tricks. That will give you a good start. You can also find some good info in The Epoxy Book, located at the System Three Resins website.

    Good Luck,

    MIA
     
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  4. ondarvr
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    ondarvr Senior Member

    Only to fine tune the subject of “waterproof”.

    Nothing is waterproof, there are only varying degrees of water resistance.

    As a coating, polyester and epoxy could both be considered waterproof, Both of them absorb water, neither allows it to pass through in sufficient quantities to rot wood when applied correctly.

    Epoxy is more water resistant than polyester, so it requires a thinner coating to be considered waterproof, which is about 10 mils. Neither of them are typically applied at 10 mils unless some glass is used (it requires multiple coats of epoxy to reach 10 mils).

    Epoxy is also much stronger, so at 10 mils it will hold up when used in an unreinforced manner (no glass), polyester would have a tougher time at 10 mils, but would need to be thicker to be considered waterproof.

    Epoxy also bonds better, so there is much less of a chance that it will peel off any substrate.

    What typically happens is people compare the two products when used in the same exact way, which is the epoxy style of use, or even less well done. This results in the polyester failing, typically from cracking, which allows water to reach the wood and start the rot process. The wood doesn’t care which resin was used, it will rot if it gets wet.

    If the polyester is used correctly it will be waterproof enough to not allow the wood to rot. Using it correctly is where most builders fail, in fact even if production boats were built with epoxy the wood wouldn’t survive, the quality of the build was so poor in the past that much of the wood wasn’t even coated well enough to keep it dry the first time the boat was in the water.
     
    Last edited: May 12, 2019
  5. Blueknarr
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    Blueknarr Senior Member


    Case in point:
    Last year a small twin jetted boat from a well known manufacturer came into my shop for minor scratch repair near bow from repeatedly being beached. I noticed and documented considerable bottom flex aft and crazing where it rested on the bunks. Rotten balsa core. While removing the cancer I noticed that one inner skin of CSM saturated with what appeared to be gelcoat fell shy of the side hull. Raw balsa for 1\2 inch by more than 2 feet was exposed to bilge water. Unfortunately the warranty had expired three months earlier.
     
  6. upchurchmr
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    upchurchmr Senior Member

  7. DCockey
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    DCockey Senior Member

    Why? All designs of stitch and glue construction?
     
  8. Blueknarr
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    Blueknarr Senior Member

    Well every design I've seen called for at least FG tabbing over seams.
     
  9. ondarvr
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    ondarvr Senior Member

    I have a hard copy of the book signed by Meade, he gave me a tour of the workshop and the projects they had going on at the time. I was there going through their training program on what products they have, and how to use them.

    He was very passionate about his designs and future projects.
     
  10. missinginaction
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    missinginaction Senior Member

    I'm just starting a stitch and glue boat from Chesapeake Light Craft. Just a little nesting pram for my boat. Without fiberglass tape over the seams there wouldn't be enough area for the epoxy to bond to. The seams are structural and subject to stress that would pull them apart. With tape you go from point loading and spread the load out across the tape and wood substrate. Much stronger.

    My experience is that Ondarvr is absolutely right. Insufficient wet out in the original layup in many spots on my old boat. I spent quite a bit of time (and cloth and resin) dealing with shoddy layups. Never where they could be seen, mainly under decks where floors were tabbed into the chine area or where floors were joined with stringers. Or up in the bow under the v-berth. Too little glass used in making the engine stringers themselves. This led to the engine settling over time and getting way out of alignment wiping out the packing gland and almost sinking the boat. As I did the restoration all these problems were corrected. It's funny though, as bad as some of the fiberglass joinery was, the hull itself, that big tub laid up in the female mold, was remarkably solid and very well done. My old boat is 46 years old, spends it's summers in the water and is blister free.
     
  11. DCockey
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    DCockey Senior Member

    Agree, but the entire surface of the hulls do not always have to be fiberglassed.
     
  12. Blueknarr
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    Blueknarr Senior Member


    Hence my use of the qualifier "some".
     
  13. DCockey
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    DCockey Senior Member

    Looks like I read your original post too quickly.
     
  14. Blueknarr
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    Blueknarr Senior Member

    Something I've been guilty of.

    No worries
     

  15. Stavbergen
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    Stavbergen Junior Member

    Thanks for all the responses.
     
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