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Thread: How much epoxy is needed to bond sheets of 3/4" marine plywood together?

  1. #36
    Join Date
    Oct 2000
    Location
    Padanaram, MA USA
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    9,471

    Default Re: How much epoxy is needed to bond sheets of 3/4" marine plywood together?

    I think I have some Anchorfast nails around here somewhere. If I could find them, I'd have to find a hammer. Nothin's simple.

  2. #37
    Join Date
    Jun 2008
    Location
    hood river oregon rgods4@msn.com
    Posts
    87

    Default Re: How much epoxy is needed to bond sheets of 3/4" marine plywood together?

    Impact driver my #1 choice, going in and out. It's only noisy when having to "work" to get something done, otherwise it sounds just like an electric drill. Careful with drywall screws - if broken off, all area around screw needs to be waterproofed/airtight. Deck screws probably same way, in my opinion. Anything bronze is golden; no problem if broken. Personally I like 'duplex nails' for a lot of my temporary holding. Allows epoxy to get on them, but it won't stick very well - pull out with hammer and block. I went to a paint roller (3" or 4" roller cover x 1/4" thick). After it's first use, let epoxy dry. Then use a rasp and remove high spots. Makes for a heck-of-a "bulldozer" when spreading unthickened epoxy over a large area, and it moves it really quick! My roller finally ran its last race after about 40 or so uses. More controllable than a spreader.

  3. #38
    Join Date
    Jul 2013
    Location
    Emerald Coast, FL
    Posts
    582

    Default Re: How much epoxy is needed to bond sheets of 3/4" marine plywood together?

    Cool screws Wizbang, star drive or square drive, either way a good bite to get them out.

    For the OP, I would focus too much on pulling panels tight tight tight other than to keep the panels from moving around, the thickened epoxy fills the gaps. Too much pressure can squeeze the epoxy right out and leave a starved joint.

    Good luck with your boat!

  4. #39
    Join Date
    Mar 2001
    Location
    FL
    Posts
    236

    Default Re: How much epoxy is needed to bond sheets of 3/4" marine plywood together?

    Quote Originally Posted by signalcharlie View Post
    Cool screws Wizbang, star drive or square drive, either way a good bite to get them out.

    For the OP, I would focus too much on pulling panels tight tight tight other than to keep the panels from moving around, the thickened epoxy fills the gaps. Too much pressure can squeeze the epoxy right out and leave a starved joint.

    Good luck with your boat!
    Agree with that, let the epoxy do the work...no screws are needed unless it makes you feel good. I use old car batteries as weights for gluing large ply panels and it works fine. In cases like outboard boat transoms I "peck" the mating surfaces before gluing for extra tooth...probably not needed but it makes me feel good.

  5. #40
    Join Date
    Dec 2003
    Location
    Portland, Oregon
    Posts
    51,169

    Default Re: How much epoxy is needed to bond sheets of 3/4" marine plywood together?

    Quote Originally Posted by wizbang 13 View Post
    As usual, the plot thickens!!
    Two layers of occume for a boat bottom!
    Is there rocker? Will they be scarphed or staggered?
    Have you considered hydrotek over okumme? (half the price and more decay resistant but heavier).Maybe two half inch layers would work?
    Yes, as usual, it takes some work to tease out the pertinent details.

    Another question - Will you be flexing the first bottom plywood layer, then gluing layer 2 to it? Or do the plans call for gluing up the panel first, then bending it into place?

    And, as usual, people tend to suggest the methods they are most familiar with. Often the only method they are familiar with. Sometimes they luck out and that particular method actually is a good idea. Sometimes not.

    There a couple of reasons I wouldn't use either bagging... or clamps & cauls. First - they are both more work than screwing or nailing. The extra hassle is worth it if you are wanting to maintain an 'appearance-grade' face for finishing bright, but not - it seems - in this case. Second - one of the hazards of this type of layup is squeezing too hard, and starving the joint. Epoxy doesn't like 'skimpy'. It's much harder to modulate pressure accurately with cauls, and impossible with a bag. You can get around that by laying laying something in the joint to keep the faying surfaces from getting too cozy. A sheet, or strips, of fiberglass is one option. Another workaround is to machine mating 'keyways' (can be nothing more than saw kerfs, or if you want to get fancy, routed dovetail slots) in both faying surfaces.

    Or you could just screw or nail.

    Or a session with the Gougeon book might recall an even better approach that we're all forgetting for the moment...
    David G
    Harbor Woodworks
    https://www.facebook.com/HarborWoodworks/

    "It was a Sunday morning and Goddard gave thanks that there were still places where one could worship in temples not made by human hands." -- L. F. Herreshoff (The Compleat Cruiser)

  6. #41
    Join Date
    Mar 2001
    Location
    FL
    Posts
    236

    Default Re: How much epoxy is needed to bond sheets of 3/4" marine plywood together?

    Quote Originally Posted by David G View Post
    Yes, as usual, it takes some work to tease out the pertinent details.

    Another question - Will you be flexing the first bottom plywood layer, then gluing layer 2 to it? Or do the plans call for gluing up the panel first, then bending it into place?

    And, as usual, people tend to suggest the methods they are most familiar with. Often the only method they are familiar with. Sometimes they luck out and that particular method actually is a good idea. Sometimes not.

    There a couple of reasons I wouldn't use either bagging... or clamps & cauls. First - they are both more work than screwing or nailing. The extra hassle is worth it if you are wanting to maintain an 'appearance-grade' face for finishing bright, but not - it seems - in this case. Second - one of the hazards of this type of layup is squeezing too hard, and starving the joint. Epoxy doesn't like 'skimpy'. It's much harder to modulate pressure accurately with cauls, and impossible with a bag. You can get around that by laying laying something in the joint to keep the faying surfaces from getting too cozy. A sheet, or strips, of fiberglass is one option. Another workaround is to machine mating 'keyways' (can be nothing more than saw kerfs, or if you want to get fancy, routed dovetail slots) in both faying surfaces.

    Or you could just screw or nail.

    Or a session with the Gougeon book might recall an even better approach that we're all forgetting for the moment...
    Even Gougeon doesn't always have all the right answers...I still remember the 5'x5' x $40 each panels I purchased from them for "westing" a 30'r. The leftover panels delaminated while sitting in the rafters of my enclosed shop waiting to be used for another project. Evidently the stuff was interior grade and sold for exterior sheathing. Most likely the reason they quit selling wood.

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