Glassing the decks- any preference?

Discussion in 'Multihulls' started by rturbett, Jun 14, 2022.

  1. rturbett
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    rturbett Senior Member

    About to lay some light glass over okume ply- 3 oz

    Curious about peoples technique- there is dry- which as some say, causes delamination as the wood sucks the epoxy from the glass

    There is wet, which seems to be a sticky challenge.

    My thought is to put a skim coat of epoxy down, let dry and sand it, following with a dry application of the cloth. Seems to me that this would ensure the epoxy/ glass adheres to the wood, and offers a simpler application method

    I would ask if I am off the wall, but there are so many other things to factor in to that opinion...
    any thoughts?
     
  2. Banzai
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    Banzai Junior Member

    I used the one coat, cure, sand down method. It was something reccomended by my designer and from memory it is mentioned in the Gourgeon Bros book as well. It creates a nice surface for draping the cloth on. Flatten out very gently any wrinkles with a new soft, hearth brush, you can never get them out when you put epoxy on them. Use a slow hardener. I used a short nap foam roller to apply the epoxy. I also pre poured enough epoxy and hardner into plastic cups so I only had to grab a pair of resin/hardner and stir so as to have minimum interuption during the process. Alternatively another pair of hands wont go amiss either, good luck
     
  3. fallguy
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    fallguy Senior Member

    Totally unnessary.

    Dryfit the fabric. Roll it on 3" tube.

    Roll the boat with 2 oz per square yard, plus some for the roller you can squeegee at the end. Lower nap rollers are best.

    Let it cure for an hour to sticky.

    Roll agin the entire boat to wet at 2 oz per sq yd.

    Offroll the glass.

    Roll with consolidation roller. Finish with more epoxy as needed.

    If you have never done epoxy work; this method may be scary, but this way all the work is primary bonded. Offrolling requires paying close attention to direction and overlaps, etc.

    In addition, next day for 3 oz, you need to do another weave fill at 2 oz per sqyd before sanding..
     
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  4. rturbett
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    rturbett Senior Member

    I understand the value of primary bonding- great point. I've done a lot of fiberglass patches, and a ton of epoxy work. I've just never done a complete fiber glassing finish. I have 2 stern sections- I'll try each method and see which works best for me.
    the last Shark I did had the best results ever, three coats of epoxy ( no glass) dried and sanded smooth after each coat.
     
  5. fallguy
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    fallguy Senior Member

    Either way is fine, but the sanding method takes more days
     
  6. rturbett
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    rturbett Senior Member

    Thanks- I'm looking forward to seeing if I can get great results with the sticky method!
     
  7. kapnD
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    kapnD Senior Member

    I like to get my fabric placed just right and smoothed out before wetting, and that’s just not possible with a tacky undercoat. Works ok for small patches, but big areas not too well. Recommend having an experienced team to do large areas over wet!
    Beware of offgassing.
    I haven’t noticed any significant weakness from placing fabric over dry, but then I don’t build ultra light raceboats or critical components for spacecraft either.
     
  8. rturbett
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    rturbett Senior Member

    Good advice- I can get helping hands easily, but not ones with experience!
    I do not know the technique used when this Shark was built. (it's number 7, the oldest surviving Shark I am aware of) I'm guessing that it was put on dry, as I was able to pull up and separate large sheets of glass from the plywood when I was disassembling. Although, its likely built in the late 50's, early 60's, so kind of amazing it held up so well.
     
  9. fallguy
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    fallguy Senior Member

    Wasn't epoxy if it sheared unless the ply rotted
     
  10. gonzo
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    gonzo Senior Member

    3 oz fabric is like what is used for surfboards. It can be done in one shot. Saturate the wood with epoxy, lay the cloth on top and smooth it, then wet and even it out with a squeegee.
     
  11. fallguy
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    fallguy Senior Member

    They are worried about drysuck which can happen with light glass. So many variables drive it, but mainly whether the wood is ultra dry or older seem to be a factor. If they wet out at 100%, but the wood demands 3 oz; the layup will fail.

    I've seen it happen even in 6 oz layups, which seems impossible because the glass only needs 3 oz, but I guess the wood demanded 4 oz.

    The same can happen with dry wood and resins with filler added. For example, take a thickened resin which is thickened 2:1 with fumed silica bonding old
    Or dried out wood. The wood sucks out the resins at the margin leaving only the filler, and what will someday be a failed joint. Worse yet is a margin with two dried woods, both pulling resins away from the bondline.

    I included some pictures of some recycled redwood used in my build; the wood sucked resins so bad, I two coated it before putty. After an initial coating and about 20 minutes, the wood was dry to the touch.



    265C53BE-EF31-4D7D-B456-02CA4DFE78D3.jpeg 262ECCAB-2CEE-44D4-B9AC-AE65B0E8ACBE.jpeg 8DFC7221-67BB-46C3-A95E-27B9A4D6EF45.jpeg
     
  12. gonzo
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    gonzo Senior Member

    Sure, but my point is that there is no need to let the resin cure and then sand it. Coating until it is saturated, regardless of how many coats, is the right way. I can see with some species like redwood that absorb a lot of resin, at least two coats will be necessary.
     
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  13. rturbett
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    rturbett Senior Member

    Cool photos- you are working on a much larger scale than I am! I can vouch for old wood sucking resin- the trampoline on this Shark is just getting a layer of epoxy on top to renew the finish (to be replaced next year- need to get it on the water) I know the first coat is going to disappear. FYI- I use my table saw as my epoxy mix station too!
     
  14. fallguy
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    fallguy Senior Member

    Actually, this is an overflow room. The build area was full of boat when I did this work.
     

  15. rturbett
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    rturbett Senior Member

    So I tackled this- had to do the dry method on the front of the boat, tried the wet method on the transoms- I did a better job with the dry method. One thing that was new to me- playing with the epoxy an hour after applying it- when it got sticky.

    I always new that fiberglass doesn't like 90 degree bends. When I tried to get it to stick to the outwale, it mostly said no, even after trying again when it got sticky. Not worried about it, but the previous builder was very successful with this. The rub real will cover this imperfection.
     
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