Prep for Glassing Plywood - to fill or not

Discussion in 'Wooden Boat Building and Restoration' started by rwatson, Aug 20, 2012.

  1. rwatson
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    rwatson Senior Member

    According to the build instructions, I am supposed to be at the stage where I can apply the fiberglass and epoxy on the plywood kayaks.

    The first coat of epoxy has been applied and sanded smooth.

    The holes from the wires are still open, and many of the seams still have gaps in them.

    Based on past experience, I wonder if I should fill all the spaces before I apply glass and epoxy. I keep envisaging bubbles or dry weave happening where the epoxy runs off the glass into the voids.

    What does everyone else do ?
     

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  2. hoytedow
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    hoytedow Carbon Based Life Form

    I filled the gaps with epoxy mixed with fine wood dust (collected from my sander). After it dried I sanded it smooth and to desired shape before glassing.

    This accidental gouge resulted when my trimmer bit lost its bearing wheel. The mix worked well.
     

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  3. gonzo
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    gonzo Senior Member

    Fumed silica is the best filler for that job. It increases viscosity without needing to add a huge amount of filler. That means it will not run when you laminate over it. The advantage is that you can putty the seams and holes, and glass right over it. There is no sanding needed.
     
  4. rwatson
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    rwatson Senior Member

    Yeah, wood flour would work ok - just a lot of friggen work.

    I had a bearing go in a router too - must have been from the same chinese factory. Lucky it wasnt on one of my boats, or I would have been really upset. Who would use a grubscrew on a shaft with no groove ?

    I know what you were doing at the time -

    have you seen one of these ?

     
  5. hoytedow
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    hoytedow Carbon Based Life Form

    I saw something similar at the Home Depot in Zephyrhills. It is a good tool but I don't think I will get one at this late stage in the game.
     
  6. PAR
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    PAR Yacht Designer/Builder

    When applying fabrics, you'll have a much easier time fairing the sheathed surface is the underlying substrate was also fair. Seems intuitive right, but many don't and then have to spend countless hours cutting out blisters, opening air pockets, etc., just because they thought they where saving a step.

    Fair the substrate, fill all seams holes, checks, cracks etc., then apply the sheathing fabric. Trust me on this, you'll get much better results if you start over a faired, continuously smooth and filled surface.

    "Well damn Ollie, I'll have to fair twice?" Well yes, you do, but the second go around on the fabric, is a whole lot easier and you have the bulk of the relatively delicate filler under the fabric, sealing it down.

    I disagree in that silica is what you want in these seams, holes etc. You want what is called for. A seam needs at least a light structural filler, possibly a heavy structural filler, so the composition of the filler mixture should reflect this. If it's just a cosmetic issue, then you don't need much silica at all. Generally, silica is to control viscosity and the the other materials provide the physical properties desired for the application.
     
  7. rwatson
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    rwatson Senior Member

    Thanks Par (and Hoyt) - you have provided the 'inspiration' to go to the trouble of filling. Silica would indeed be too hard a substance - fairing it back would be a nightmare, and so white against the wood.

    It really only needs soft stuff to hold the shape of the hull. I remember chasing 'bubbles' in previous builds caused by problem substrate, and it made for a lot of work as Par reminded me.

    I swore that I was going to paint these suckers, but my missus got all inspired by the polished wood, and wants two dining tables. Oh well, you can always paint out the rock damage later I suppose.

    So - off to make some wood dust :rolleyes:
     
  8. hoytedow
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    hoytedow Carbon Based Life Form

    I keep a jar into which I empty my sander dust collecter for just such situations.
     
  9. PAR
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    PAR Yacht Designer/Builder

    Sander dust is usually a very coarse substitute for wood flour. Flour particles are typically dozens of times smaller, which is why they make smooth fillets. They also have to be dry, really dry to be effective. Don't get me wrong, you can use sander dust, but the fillets will be lumpy, rough and will need to be over filled and sanded down for a smooth finish. I've made my own dust for a few years now, with an old flour mill stone and 1/2 HP motor. It takes quite a while and a lot of energy (drying) for just a little bit of flour. Fortunately, I make gallons of dust daily, most of which is burned, because it's just to coarse. Only the smallest bits that fall through a screen get ground up. It can take a day of mill time to produce 5 pounds of flour. Considering at full retail I can buy a 5 pound sack of hardwood flour (the best) for less than $20, I wonder why I bother.

    Simply put there's a pretty huge difference in particle size and the small, well ground flours available are in the 50 micron range, while sander dust, even from the finest papers will be hundreds if not several thousands of microns. If it's under 'glass and to be painted who cares, but if filling cracks, checks and coarse grain lines, maybe under varnish you'll want flour.

    Speaking of flour, wheat and rice flour work very well and offer the creamy nature you'd expect. Adding some talc (averaging 25 microns) will improve it's creaminess. Mixing wood dust with talc can improve things and modify color too.

    Something to think about . . .
     
  10. rwatson
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    rwatson Senior Member

    I seldom sand plywood with a sander. I got some scrap ply today and generated some dust.

    25% done. Very tedious !

    Whoops, just noticed Pars points on wood flour. I agree totally. The orbital sander produced quite fine dust with an 80 grit pad, and I mixed in some West Systems fairing compound to smooth it out. I think it will sand ok, it certainly applied smoothly.
     
    Last edited: Aug 21, 2012
  11. hoytedow
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    hoytedow Carbon Based Life Form

    I agree too but I don't need that level of fineness for the work I do. I just fill the voids and run the router over it again before glassing. Once it is sanded and painted you would not likely notice given the crude carpentry evident every where else on the boats I built.
     
  12. ancient kayaker
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    ancient kayaker aka Terry Haines

    Sounds like you sorted out the filling question but I didn't see anything addressing the glassing. The Kayak Forum has a good discussion thread dealing with that which may be of some help -

    http://www.kayakforum.com/cgi-bin/B.../id/219191/sbj/strip-fiberlassing-procedures/

    - and there's this web page in my favorites list for some day when even I feel the need for glassing -

    http://www.laughingloon.com/epoxy.html

    EsitL the filling's probably done already but I find a turkey baster (for big stuff) or a vet's hypo (for detail stuff) great for filling long gaps between the planks: saves a lot of time. Wrap a cloth around it so you don't set off the epoxy too quickly. System Three (and probably West Systems by now) sell filleting and fairing epoxy formulations in a caulking gun-compatible cartridge with a self-mixing tip: the tip can be taken apart and cleaned but it's cheap. The carttridges are a bit expensive but super fast and convenient.
     
  13. rwatson
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    rwatson Senior Member

    The fibreglassing is the least part of the mystery. If I could start again, I would forget about the syringes, turkey basters and all that stuff for the initial chine epoxying, and simply get a narrow brush to lay a strip of epoxy along the chines. The runs and overfills even with a syringe are a real nuisance.

    Likewise, the original advice not to bother with filling the holes before the fibre lay, might not have been as far off the mark as I feared. Certainly, dressing up the areas surrounding the filled holes is tedious, and may well make for visible patches after the final coat has been laid.

    It's not that critical on these particular craft, as they have a semi-experimental purpose.

    But, if I was trying to produce superior finished hulls, I would definitely rig up some sort of jig system to hold the panels, and forget about drilling wire holes.
     
  14. latestarter
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    latestarter Senior Member

    I am part way through cutting the ply panels for a canoe at the moment.
    It will be my first build and intended as an experiment.
    My aim is to use adhesive tape to hold the panels together until it is tacked.
    I will start a thread so you can learn from / be amused by my follies. :)
     

  15. rwatson
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    rwatson Senior Member

    Good luck LS. I think you may be dissapointed using tape. The stresses and alignment of the panels require a lot of pressure, and adjustment.

    No way tape can handle that pressure.

    Unless you have a very rigid inner frame, with some powerfull ways to force the plywood onto it, you are gloing to need wire.
     
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