How to bond foam

Discussion in 'Fiberglass and Composite Boat Building' started by Mark C. Schreiter, Dec 29, 2020.

  1. Mark C. Schreiter
    Joined: Nov 2020
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    Location: Tampa, Fl

    Mark C. Schreiter Junior Member

    I believe I received all my materials to start on an all composite, foam core 14 ft flats skiff. I ordered 9 sheets of 4lbs foam per the plans, however I “re nested” all the parts to fit only 7 sheets. The two extra sheets I’d like to use for??? Maybe a console or widen the bow deck or whatever else.

    Sooo my question is, what is the best way to bond foam together on edge?

    my first thought was to sand about 1/16 deep and 3” wide on both sides of each of the joining pieces, use a little thickened epoxy on the butt joint and a layer of 1208 6” wide tape in the recesses.

    Most of the foam will get 2 layers on each surface of 1208 so the seems would have 3 layers on each side.

    what are your thoughts?

    thanks in advance

    -Mark
     
  2. Mr Efficiency
    Joined: Oct 2010
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    Mr Efficiency Senior Member

    No need for anything sophisticated, whatever is most convenient to hold it together, so long as it doesn't react with the resin you use. The structure does not depend on that foam for its strength, its job is to hold the skins apart. Just think of end-grain balsa squares.
     
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  3. Mark C. Schreiter
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    Mark C. Schreiter Junior Member


    Good point.

    So if a section of deck has a span of say a couple feet and the plans call for a solid pice of laminated foam, I technically should be ok to splice a couple pieces of foam together?
     
  4. Mr Efficiency
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    Mr Efficiency Senior Member

    Just butt it together like a patchwork quilt, quite often you end up with offcuts that can be used, and on flat areas, that is easily done. Too expensive to waste.
     
  5. Mark C. Schreiter
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    Mark C. Schreiter Junior Member

    I shall try. I was wondering why the original drawings wasted 2 full sheets.

    Thanks a lot.
     
  6. Mr Efficiency
    Joined: Oct 2010
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    Mr Efficiency Senior Member

    You don't need to fuss about what you use to stick it together. Chewing gum would do ! It is probably better not to leave gaps that water can travel through, though, if the laminate gets damaged, I think on occasion I just used a lightweight Q-cell bog to "mortar" the joins.
     
  7. Mark C. Schreiter
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    Mark C. Schreiter Junior Member


    Chewing gum would cut down on epoxy costs. Lol
     
  8. wet feet
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    wet feet Senior Member

    Hot melt glue will work and is reasonably cheap and quick.
     
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  9. Mr Efficiency
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    Mr Efficiency Senior Member

    Yes, I have used it, the thing about it is that it takes a while to set up, as the foam keeps the heat in.
     
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  10. kapnD
    Joined: Jan 2003
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    kapnD Senior Member

    If you need large foam sheets or strips, say to lay over frames, you can fasten them with glue of your choice, and a light tape over the joint. Sometimes a few small dowels help,alignment.
    I have used just a light matt tape with some success, it is thin enough that it won’t require removing any foam, yet not so rigid that it makes a flat spot when bending the panel. if you tear, not cut, the edges of the mat, it will readily disappear beneath subsequent laminates.
     
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  11. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    I use raptor staples, work well, but the gun and staples set you back 250$.

    Here is a panel made up of junk, all stapled together for a kitchen cabinet panel. The white aquaplas is on the face in case I use any mechanical fastenings.
    3E77767F-6980-4976-A8FE-6233062C6233.jpeg
     
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  12. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    I try to avoid using tons of seams on hull and other structural components, but of course there are some in a 33' long panel!

    I try to use up scraps on less critical places.

    All my work is wet bagged and so there is epoxy flowing like crazy into all the seams, but I do increase corecell wetout rates with lots of seams like the kitchen panels I shared.
     
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  13. wet feet
    Joined: Nov 2004
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    wet feet Senior Member

    Its nice to know that somebody else in the whole world uses torn edges of mat.It used to be fairly common,but has become quite a rarity for some reason.
     
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