help with laminating several foam sheets together

Discussion in 'Fiberglass and Composite Boat Building' started by Tungsten, Aug 10, 2019.

  1. Tungsten
    Joined: Nov 2011
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    Location: Canada

    Tungsten Senior Member

    I have some 1400mmx450mmx12mm corecell A 1200 cut offs i^d like to laminate together.What is the best way to join the long sides together?This is for a small boat hull ,skins will be approx 2mm thick.
    The boat is a 14’ Jon flat bottom. Construction will be stitch and glue.
    First thought is to build a strong back with bulk heads in place so I have a form.
    Second would be to build a flat table to butt join the foam ,skin one side then stitch.
    Looking for ideas thanks.
     
    Last edited: Aug 10, 2019
  2. Mr Efficiency
    Joined: Oct 2010
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    Location: Australia

    Mr Efficiency Senior Member

    How about contact cement ? Or maybe resin will attack it.
     
  3. philSweet
    Joined: May 2008
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    Location: Beaufort, SC and H'ville, NC

    philSweet Senior Member

    Build a 16' table and cover with Melamine or Formica and coat with a mold release such as Maguiar's mold wax (about 8 coats) or some other release agent. Layout the panel, adding any pockets, nonskid pattern sheets, or edge flanges to the table. Lay the glass skin down and wet it out with a good, slow laminating resin and let it start to kick. Thoughoughly coat the foam with resin - two or three wet coats on faces. - this can be done with a faster resin. Use a slightly thinkened resin to bog the sheets onto skin. Don't try to scooch them around, just lay them down and walk away. The bog coat should be the same slow laminating resin - you don't want to add any heat at this point. It helps to weight the panels down slightly, but do it evenly. I've laid plastic and plywood down and shoveled sand on top. Once set, you can bog the panel joints. If necessary, kerf the joint first. Or use popsickle/tongue depressors sticks as spacers when placing the foam. At this point, you have a choice. You can skin the foam panel as it sits now, or pull the panel and build a shinier skin on the table and bog the foam panel to it. You'll usually need to do some careful fairing of the foam either way, so coat with resin then trowel (or spray) a decent layer of easy to sand resin (lots of bubbles) let that set rock hard, and staple sand paper belting to a 2 x 4 and longboard the whole thing.

    TLDR: Don't glue them together. Bog the kerfs after they are in place.

    PS I could build about 20 jonboats out of lumber in the time it will take you to do this if you are starting from scratch.

    An alternative might be to build the entire hull out of 6mm plywood stitch and glue. Then bog in the foam pieces on each panel. Stop the foam 3" short of all panel edges and bevel the foam 45 degrees. Then cover the floor foam with 3mm ply, Tab all chines and exposed foam edges with 12 oz biax and glass the entire inside with two layers of 10 oz cloth. That should be pretty durable, and it makes more sense in terms of methods. Stitch and glue isn't very handy on composite sandwich construction. If you go that way, bevel the foam as described above and just have a single skin at the panel edges where you stitch them together.
     
    Last edited: Aug 10, 2019
  4. Tungsten
    Joined: Nov 2011
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    Location: Canada

    Tungsten Senior Member

    Thx Phil,ya I agree building out of ply would be easier.I have enough of these foam panels for a 14'boat ,if I dont use them now my fear is they will never be used.
    Could I tape the seams with biax say 6", bevel the edges then when cured flip over and bog the voids then laminate the skin?With plastic and weights I could get the edges to line up as the tape cures.

    Thanks,
     
  5. philSweet
    Joined: May 2008
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    Location: Beaufort, SC and H'ville, NC

    philSweet Senior Member

    You would only need 2" or 3" of tape. I'd lay a board along the joint and bash it with a hammer to get a rebate in the foam, then screed the joint level after taping. You only need a tiny bit of indent. But you do need a resin rich bond. The rebate helps pool resin. The old CSM could be accurately made into narrow strips by laying a straightedge on it and running a squeeze dispensing bottle with acetone along the straightedge. It gives you a naturally feathered edge and was plenty resin rich and was cheap. I'd use that. But tell the vendor you want a seizing that dissolves in acetone. 3/4 oz CSM 3" strips should work fine.
     

  6. Tungsten
    Joined: Nov 2011
    Posts: 465
    Likes: 10, Points: 18, Legacy Rep: 75
    Location: Canada

    Tungsten Senior Member

    Not sure the 12 lb density foam will compress that easily. May have to cut rebates for the tape not sure. Epoxy will be my resin. Looks like I need to build a table. Thanks for your help.
     
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