Advice sought...screws into epoxy

Discussion in 'Fiberglass and Composite Boat Building' started by massandspace, Jun 18, 2021.

  1. massandspace
    Joined: Sep 2017
    Posts: 39
    Likes: 0, Points: 6
    Location: Salt Chuck

    massandspace Junior Member

    Hello

    Situation: I will need to screw multiple fasteners into a composite (epoxy/plywood/glass skins) structure later....the location of which are not set yet. There will be a lot of screws along a single line. This is exterior....will get very wet, so how to keep the core dry is the question...

    I cannot enlarge holes and refill with thickened epoxy now (as I do not know the final screw locations) and later there are serious time constraints that will prevent me from doing the same process. I just need to quickly drive in the screws later and maintain no water to ply core contact.

    I have 2 ideas. One is to rout a groove into the structure and refill with thickened epoxy. But won’t the screw just blow apart the cured epoxy later? Or if not, what type of filler(s) would give the best chance of taking the screw? I think binding it with chopped stand might help a lot???

    The other idea is to embed a bar of Starboard fiberboard into the structure. That material is pretty soft....will accept a screw without splitting or cracking (too much). And cannot rot.

    Any other ideas welcome.

    David
     
  2. Blueknarr
    Joined: Aug 2017
    Posts: 1,206
    Likes: 273, Points: 83
    Location: Colorado

    Blueknarr Senior Member

    Plywood core
    Do it r
    Correctly now or repair latter.
    There is no quick way that won't rot!!@!!
    Epoxy plugs will split less than the plywood they replace. Chopped strand helps a lot. So do pilot holes.
    Grooving is acceptable if deep enough. Epoxy must be deeper than the screw length to be fully effective.

    Screws pull out of starboard easily.
     
  3. Rumars
    Joined: Mar 2013
    Posts: 1,187
    Likes: 561, Points: 113, Legacy Rep: 39
    Location: Germany

    Rumars Senior Member

    In the area in question, remove the plywood core and replace it with the same thickness of G10 plate.
    For thickened epoxy, chopped glass fibre and microfiber, or a proprietary blend like West 404.

    What are you attaching and how thick is the plywood? G10 can be tapped and you can use bolts instead of screws, ensuring absolute water tightness forever.
     
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