Help support the WCHA Forums by making a tax-deductible donation!

Fiberglass question

Discussion in 'Strippers, Stitch-n-Glue, and Other Wood Composite' started by Dabluz, Sep 11, 2012.

  1. Dabluz

    Dabluz Curious about Wooden Canoes

    I will be fiberglassing my old cedar canoe. There is a lot of great info on the internet but nowhere is there mention as to how to finish the fiberglass job at the prow (pointy part) of the canoe. Do I try to smooth the fiberglass cloth so that it fits tight at the prow and worry about the wrinkles on the sides of the canoe or do I just trim the fiberglass and overlap the cloth at the prow? How much overlap should I have? In my mind, this overlapping will make a large bulge at the prow. If the overlap is too large, it must show even after a couple of coats of epoxy and paint. Do I let the fiberglass harden and then sand off the extended fiberglass joint? Anyway, this part of glassing the canoe is a mystery for me.
     
  2. Todd Bradshaw

    Todd Bradshaw Sailmaker

    Normal fiberglass does not wrap around corners very well, so you want to glass up to a point just short of the stem and stop. This also allows you to concentrate on the glassing job for the rest of the hull, making sure there aren't any bubbles or problems (which is a big enough job all by itself). Then you want to let those main fiberglass layers harden just enough that you won't disturb/smear/mess-up the glass as you work on the stems before proceeding. In the mean time, you start cutting strips of fiberglass cloth for the stems from your roll of cloth. Depending on stem width, these may typically be 3"-4" wide - enough to cover the stem and overlap by an inch or so onto the main hull's cloth. The key to this whole process is that rather than cutting these strips square to the weave of the roll of cloth, you cut them at a 45 degree angle to the weave (diagonally, called "on a bias"). A bias-cut strip will, with some coaxing, wrap neatly around a very tight corner or a very complex shape. You want a couple layers of these bias strips (which can both be applied at the same time) and if desired, you can also add a couple more short sections down below,in the lower stem area where you might encounter rocks.

    Once all the glass has been applied and has stiffened up enough that further work won't disturb it, you can start rolling coats of plain resin on the entire hull to fill the fiberglass cloth texture. No sanding should be done at this stage. You risk bruising the glass and also green resin dust is not something you want on your skin. Keep applying filler coats until the cloth texture on the main hull part disappears and then add one more. You will probably still be able to see some level changes where the bias strips were applied, but they will be substantially smaller than they were and will be dealt with later. Let the epoxy cure for about one week. You want it completely cured before you start sanding.

    When it's cured, wash the surface down with plain water and a scotchbrite pad, dry it and start sanding (80 grit or so). Sand the hull smooth and in the process, feather out any lumps at the stems where the bias strips were applied. That's the only spot on the boat where you actually want to be sanding down into the weave of the cloth a little bit as needed, in order to achieve a fair shape and smooth surface.

    A couple other things......... If this is a rib and plank-style canoe, every tack head dent and every crack between the planks needs to be plugged with something before glassing. Otherwise, the resin will drain out of the cloth over these gaps. This leaves what looks like spots of screen wire over the holes and they are extremely hard to fix and make watertight.

    Then there is always the question "Is fiberglass the best and proper way to fix this boat in the first place?" For most of the boats that we see here, it really is not and can spell eventual doom for a boat that has managed to survive many years and could survive many more with the proper restoration. Not knowing what your "old cedar canoe" actually is, it's impossible to say more about it at the moment.
     
  3. OP
    OP
    Dabluz

    Dabluz Curious about Wooden Canoes

    Wow....great stuff! No mention of this on the internet.

    Yes....my canoe was originally a wood/canvas canoe. It had been redone at some moment with a thin cloth material (maybe dacron) or maybe fiberglass but I guess they used so little resin that nothing stuck to the hull. Yes, I could have re-canvassed the canoe but it seemed too fragile for that. It's a canoe built by Picard of the Huron group near Quebec City and I'm sure that it was a canoe made to be sold via Simpsons Sears or Eatons in Canada. Even when new, it was probably not a very robust canoe and the reason that I have decided to use fiberglass and epoxy resin is to have a stronger canoe. Weight is not a problem....I have a 14 foot Sportspal for the long portages. The 16 foot square stern canoe that I am working on will be used principallly for fishing.

    I even plan to add some reinforcement at the bow by adding extra ribs and I will be adding 2 corner supports made of maple at the stern instead of the angle iron and I will even add a maple support from the bottom of the canoe to the transom and also fit a wooden wedge inside the bow of the boat. The front deck will be maple too. Even though I have a nice maple plank that is 1 1/4 inches thick, I may use cherry wood instead. I also have high quality 11/16 inch maple plywood to add to the inside and outside of the transom.

    I will be painting the fiberglass after the 2 coats of resin and 2 coats of spar varnish. I haven't decided on the colour of the canoe yet. Burgundy really looks nice and different from all of the other canoes that I see.

    For the gaps and cracks in the hull, I have used up close to a quart of plastic wood and I will be doing the first sanding job tomorrow. I'm sure that I will have to add more plastic wood to the nail heads and to a few small dents in the hull.
     
  4. Todd Bradshaw

    Todd Bradshaw Sailmaker

    The typically quite thin layer of fiberglass on the outside of a wooden canoe hull doesn't actually add much "strength" to the boat at all. Most of the stresses that a canoe hull gets in use are from forces pushing inward on the hull - beaching, hitting rocks, waves, and simply the weight of the paddlers forcing the hull down into the water and the water pushing back. These forces put the outside skin of the boat in compression, where a thin layer of external glass does virtually nothing to help. By itself, a laminate made of one or two layers of 6-8 oz. fiberglass saturated with epoxy is about as stiff as a plastic milk jug and would add about the same tiny amount of resistance to compression that an empty milk jug would have if you poke it with your finger. If you hit something, it will flex and basically just move out of the way while the impact shatters the wooden structure inside the boat (which is what is providing the actual resistance to compressive forces, no matter what it is covered with on the outside).

    The true "strength" of fiberglass is its tensile strength. The strong, straight, thin fibers resist being pulled apart quite well, and better per ounce of weight than a lot of other fibers. In order to take advantage of this strength, you have to put them in a place where the forces they encounter are trying to pull them apart, not push them together or just bend them as happens from compression on the outside of a canoe hull. If you look at something like a stripper canoe with glass both inside and outside, it is the inner glass that is providing the tensile strength to resist compressive forces like rocks pushing inward on the bottom, not the outer glass layers. This is why the common rookie mistake of reducing the laminate on the inside of a stripper to save a few pounds is such a terrible idea. They may save a few pounds alright, but they'll probably also reduce the compressive strength of the hull (the strength that it actually needs out in the real world) drastically. They build a boat that does fine if you plan to put it in the water and jump up and down in it (which does put the outer glass in tension where it can contribute strength to the hull) but they will have drastically reduced the hull's ability to survive an impact with a rock. On a rib and plank hull, there is no inner glass, the outer skin (whatever it is) isn't in a position to add compressive strength and so that strength has to be provided by the wood structure. To boost it substantially with outer layers of fiberglass you would need to add enough glass to basically build a stand-alone fiberglass canoe hull - and who wants to tote a canoe around which weighs nearly twice as much as it should?

    The one "strength" that a fiberglass outer skin can add to a wooden canoe hull is increased abrasion resistance, though the difference compared to canvas and a good filler isn't as much as a lot of folks think. In some ways, I suppose you could also say that the glass skin is potentially a lower maintenance covering, as you're less likely to have problems like paint cracks from the skin expanding and contracting - and the glass skin won't absorb water in use and add temporary weight to the boat. On the other hand, if your maintenance ever involves replacing cracked ribs or planking, the glass skin will make that much more difficult. You also want to be sure to maintain the varnish on the wood carefully. Water-soaked wood up against a fiberglass skin is a formula for rot.

    So, in the long run, it's like everything else in life, there are trade-offs. With the fiberglass, you gain a few things and you lose a few things, but don't think for a second that fiberglassing the outside of a wooden canoe hull is really going to reinforce the wood or make the hull stronger, because it's just not going to happen.

    p.s. In order to bury the glass enough to avoid sanding into it and weakening it, you will probably need more than two coats of resin - and the spar varnish under the paint won't do anything at all and may actually shorten your paint life by exceeding the proper coating thickness. Just sand the resin surface smooth to about 100-120 grit and paint the boat.

    FYI - this is my fiberglass-skinned 1972 Old Town. I've been there, done that, got epoxy on the T-shirt and it came out pretty nice. Would I do it again? Probably not, as I think there are better options.
     

    Attached Files:

  5. OP
    OP
    Dabluz

    Dabluz Curious about Wooden Canoes

    My old canoe would have been a real headache if I wanted to stretch canvas on it. I've also seen quite a few canvas covered anoes with ripped canvas just laying around people's cottages. I don't think the gunwales would not have withstood the tension. The edge of the gunwales were pretty rough too. Anyway, I had the opinion that canvas was inferior to fiberglass and epoxy resin. I've played around with fiberglass and epoxy resin before when I made a flatbottom 12 foot rowboat (stitch and glue method) out of 1/4 inch plywood. Even though it was a flat bottom 48 inches wide, it did have a bit of "rocker" and worked marvelously. Yes, the bottom flexed quite a bit but the sides didn't flex much due to the curvature. The problem was that I could not find marine quality plywood and water seeped into the wood. The flexing caused small cracks in the paint. It was fun to make though and took about 3 days of work and waiting time.

    The covering on my canoe was not stuck to the wood except in a couple of spots where it had been patched with fiberglass or what ever was used on the canoe before I got it.
     
  6. Kathryn Klos

    Kathryn Klos squirrel whisperer

    I sincerely hope you attend a WCHA chapter event or our annual Assembly, where you would be treated to dozens of canvas-covered canoes, some of which would be 100 years old or more, fully usable and looking wonderful. On a ribbed canoe, canvas is the preferable covering, not simply for historical reasons but for reasons Todd mentioned. I'm glad Todd jumped in to reply to your question before those of us with memories of a torturous fiberglass-removal began a reply with NOOOOOOOOOoooooooooooo. But I hope your opinion of canvas is in the past-tense (you HAD the opinion that canvas was inferior to fiberglass and epoxy resin) and that you now understand that canvas belongs on a ribbed canoe, but every canoe-owner has the right to repair/restore as he/she chooses. I'm glad Todd was here to give you the answers you needed for your canoe.

    Kathy
     
  7. sjmoore69

    sjmoore69 Curious about Wooden Canoes

    this was very educational. thanks for sharing all of your experience.
    steve
     

Share This Page