Resin viscosity in hand layup

Discussion in 'Fiberglass and Composite Boat Building' started by hardcoreducknut, Jan 12, 2017.

  1. hardcoreducknut
    Joined: Aug 2011
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    hardcoreducknut Junior Member

    I'm considering doing another boat build via stitch-n-glue using epoxy.

    One of the issues I faced with my last two builds was trouble with substrate adhesion due to outgassing, and lack of penetration with the epoxy through the current layer I was working on. This caused a lot of sanding, grinding, waste, etc. I was using high viscosity epoxy at the time.

    What situation is one viscosity of epoxy (low, med, high) more appropriate than the other? Would I have better success with low?
     
  2. Scot McPherson
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    Scot McPherson Senior Member

    The best scenario is to lay another layer up when the previous layer is in the green stage, this allows all the layers to bond together chemically.

    If you have to let the previous layer cure first, then you MUST scuff the previous layer with 60-80 grit sand paper THEN clean it with ACETONE in order to permit the layers to be bonded mechanically and the acetone wash avoids any blush or other contaminant from preventing proper adhesion.

    The viscosity is more about what job you are performing, and will the epoxy hold on while wet.

    Additionally, if you are talking about your first layer, chose A/C plywood instead of A/A and put the C side on the outside. This is the rougher finish, and will help the epoxy and glass to adhere to it.
     
  3. hardcoreducknut
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    hardcoreducknut Junior Member

    Scot,

    Thanks for the response.

    I used Plascore PP Honeycomb as my core material. I'm unsure what you mean by green stage but I'm going to guess that it's while it's still wet and/or tacky. I had done as you said with sanding after curing, then wiping off with SLX as opposed to Acetone and letting that evaporate.

    The next build will be done layer after layer in succession, however my hull has an enclosed top thus the top and bottom halves must be joined together. This was one place where I encountered problems.
     
  4. upchurchmr
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    upchurchmr Senior Member

    "Additionally, if you are talking about your first layer, chose A/C plywood instead of A/A and put the C side on the outside. This is the rougher finish, and will help the epoxy and glass to adhere to it."

    This is a continuing bad suggestion.
    Epoxy will bond to any plywood and doesn't need the "bad side" of plywood.
    For a boat, don't ever use something as bad as AC.

    If you have some teak plywood you might need to do something special, but any other common boat building wood will work without sanding/ roughing.
    Try it you will like it.
     
  5. PAR
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    PAR Yacht Designer/Builder

    There are several issues at play here, lets pin them down.

    Outgassing occurs on raw wood that's being given sealing coats of epoxy. If the epoxy is pooling on the surface and the substrate warms in the green stages, air bubbles will rise up, through the pools, leaving little pinholes and bubbles everywhere. To prevent this, insure the substrate is cooling during the process or us my technique (see my site's tips and tricks page) for applying epoxy to raw wood, where it doesn't matter what the substrate temperatures do, in the first stages of the cure.

    Next is using the appropriate procedures to apply goo and/or fabrics to a substrate (plywood, foam, whatever). Log onto WestSystem.com, SystemThree.com and my site to get free downloads of manuals that can greatly improve your understanding, of the techniques and proceedures employed. These processes are all about the right technique, if good results are desired. Skip a step or two and you can quickly screw the pooch, which you've already experienced to some degree. Again, to avoid these (and a whole bunch of other ones), bone up on the information available and maybe practice a bit on some scraps to get a feel for stuff, first, before the costly goo hits the expensive substrate again.
     
  6. Scot McPherson
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    Scot McPherson Senior Member

    A vs C is not good vs bad, its finely sanded versus rough surface...there is no difference in the ply quality, the interior laminates, the void potential, nor the glue. It's about the surfaces and the surfaces only.
     
  7. upchurchmr
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    upchurchmr Senior Member

    How many footballs allowed in the C side?
    I think you are mistaken.
     
  8. Scot McPherson
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    Scot McPherson Senior Member

    have you considered inspecting the plywood before you buy it? No one said to buy plywood with footballs in it
     
  9. upchurchmr
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    upchurchmr Senior Member

    Every piece of AC plywood I ever had has footballs.
     
  10. endarve
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    endarve Junior Member

    I don't know about offshore ply brands but in the US the APA says fillers (footballs or resin) are ok on A,B & C faces of marine and exterior ply. I used AB exterior to sheath two sailboats (42' & 32') and no problems. 3 yrs later the 42'r sailed from N. Carolina to Alaska, then down to Samoa and back to Florida. 10 yrs and no issues. The ply was epoxy glued to the old wood hull and fastened with bronze boat nails. I set the heads down and filled over with epoxy. NO cloth but several thick coats of epoxy. Yep, I was on a budget but the ext ply worked.
     
  11. PAR
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    PAR Yacht Designer/Builder

    Only the APA uses the arabic coding system for plywood. The two or three letters describe mostly the face finish, but also panel construction under a specific grade subsection. The APA marine grade is marked Marine PS 1-95 in either an AA or AB grade sheet. There is no such thing as an "Exterior/Marine" sheet, though the "Exterior" siding also carries the PS 1-95 build quality mark and is essentially similar, typically other than the faces and minor panel construction differences (internal void and defect counts, etc.). The Marine AA or AB, PS 1 -95 is usually a slightly better panel than a AB Exterior sheet. Commonly I've found the A faces to have no defects, knots or blemishes on the Marine PS 1-95, I have seen repairs on AB Exterior sheets, built to the same standard (PS 1-95). Yes, there is a difference in the quality of the veneer on a C face, particularly when compaired to an A face. A C face will permit several repairs, defects, lots of knots, pith pockets, etc., meaning the veneer used on this face, isn't nearly as good as the A face.

    Simply put, they just don't change the ink stamping machine logo at the end of a AB Exterior sheet run, with a Marine AB label, so they can just keep running the same lot. Even though the APA grading system is voluntary, most of the manufactures build marine sheets to a tighter tolerance. If you break open a couple of pallets of APA Marine and compare their general quality against a couple of pallets of AB Exterior, you'll quickly see the difference, even though the PS 1-95 grade doesn't ask for any special attention.
     
  12. SukiSolo
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    SukiSolo Senior Member

    I'd second PAR's wise advice especially on temperature of the substrate. Also often worth a pass with hair dryer/paint stripper gun/Propane torch over the just applied resin to get the resin to run in and sink into the pores and allow small air bubbles to burst free.
     
  13. PAR
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    PAR Yacht Designer/Builder

    Warming the work, just prior to epoxy on raw wood is a well tested method to help eliminate outgassing. Waving a torch or heat gun over the work, that is outgassing is often a futile affair, simply because the bubbles never stop coming and you're just chassing your own tail. Admittedly, I've chased many a bubble with a torch.

    If you do use a torch or heat gun on freshly applied resin, then you'll lower its viscosity a bit, but I've found my "mash and go" technique works better and eliminates the possability of outgassing, when coating raw wood or other porous surfaces.

    It divides into two basic areas, substrate temperatures, which many have little control over and providing places for the bubbles to form. If the substrate rises in temperature or the resin is cooler than the substrate, bubbles will form in the resin and rise to the surface. I handle this by not providing a place for the bubbles to form, regardless of substrate temperature, on initial raw wood coatings.

    So these are the approaches, - insure the substrate is cooling and is lower in temperature than the resin and/or appropriate application of raw wood coats, whereas there's no place for bubbles to form (any pooling resin). Have a look at my Tips and Tricks section where I cover it pretty well and your outgassing issues will end.
     
  14. Tungsten
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    Tungsten Senior Member

    I think this thread has gone a little off course,the OP is not using plywood.

    Heating the epoxy will reduce the viscosity,I think most hand layup brands are around 600, with heat you can reduce this too 300.
     

  15. pauloman
    Joined: Jun 2010
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    pauloman Epoxy Vendor

    trying not to be self promoting, but my basic no blush epoxy has bubble breakers in the part A than addresses some of the issues mentioned, plus non blushing. wet out has much more involved than viscosity. I have an epoxy paste used with fiberglass cloth for pipe wraps and it wets our fine. - won't mention my company.... note that epoxies take over a week for full cure so the chemical bonding is in place for about a week.
     
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