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

  1. #1
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    Default How much epoxy is needed to bond sheets of 3/4" marine plywood together?

    I need to laminate several large sheets of 3/4" okoume marine plywood with epoxy.
    I expect to fasten the sheets together with temporary screws about every foot, plus edge clamps. All the necessary holes can be pre-drilled.

    I plan to wet both plywood faces with neat epoxy, using plastic scrapers, and then join the sheets, almost green-wet-almost green, with more epoxy.
    I have not yet decided upon what thickening agent to use for the center layer (fibers vs. fumed silica, or both).

    I want to estimate the amount of mixed epoxy resin + slow hardener that is required for the epoxy layers,
    in order to prepare myself and one helper for mixing and spreading multiple small batches of epoxy in a short time.

    I have read (e.g. newporterworks.ning.com) that 9 oz of Raka resin + slow hardener might be enough for each layer of epoxy
    to join two 4 x 8-foot sheets of okoume. Is a total of 27 oz for 2 sheets a reasonable estimate? Of course I can prepare more if necessary.

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

    If the question is about volume, i'd have thought half a liter would be heaps for two sheets (one mating surface) - that's half a quart in American i think. Not sure what it is in ounces.
    I'd have thought, with A/A grade surfaces, as long as the bottom sheet is flat, both surfaces are well saturated and there's one more generous layer of neat epoxy, you wouldn't need thickening. Fibers will only create a gap, no?

    Its an odd thing to want to do - what are doing with it?
    You can buy pretty thick beechwood ply - no screw holes.....
    "People should be able to access these benefits [Social Welfare] as a matter of right, with no more loss of their own standards of self-respect than would be involved in collecting from an insurance company the proceeds of an endowment policy on which they have been paying premiums for years."
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  3. #3
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    Default Re: How much epoxy is needed to bond sheets of 3/4" marine plywood together?

    When I have used WEST I could cover a 4'x8' sheet of plywood with about a half gallon total mixed volume. So making what amounts to three coats, two unthickend and one thickened, you'll want something over 1-1/2G per bond. Mix in small batches so you don't go all exothermic. Different epoxies on different woods and grains have different coverage rates.

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

    I don't know about epoxy for this application but I've glued many a sheet of ply to another using Titebond 2 or 3. That takes about a cup of glue. They won't separate. If you have access to a vacuum bag, the job will be much easier and you'll get a better join.

    Jeff

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

    You do not need to pre drill. Get inch and a quarter construction screws from home depot and an impact driver. Send a LOT of em in, that is the trick. An impact driver gets em out as well as it puts em in.

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

    If you'll be using these for boatbuilding, I'd sure be tempted to use weights instead of screws so you don't have all those holes to seal or let moisture into the plies. But Wizbang knows his stuff and that method will ensure a tight bond.
    "The enemies of reason have a certain blind look."
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    Default Re: How much epoxy is needed to bond sheets of 3/4" marine plywood together?

    The last thing you want to do is skimp on epoxy for this task. Several times now I've glued up 1/4 inch sheets of plywood to make 1/2 inch thick sheets for bottom bow panels that had too much curvature to do up in 1/2 inch ply.

    For a 30 inch wide by 8 foot long bow section with a large gore cut out of it, say 15 square feet, I used 15 ounces of straight epoxy to wet out both panels and 18 ounces of epoxy thickened with silca to make putty. I smeared it on thick and fast with a big putty knife. I used sheet rock screws roughly every six inches along the edges, and on roughly 8 inch centers everywhere else. Power the sheet rock screws in fast (dont predrill) with fender washers or little squares of ply as washers under the screw heads. Cut little pieces of plastic garbage bag to go under the washers so that the washers don't stick to the ply. Use plenty of epoxy so that there is no after thought or worry about voids or dry areas. You don't have to use the most expensive epoxy either.

    Laminating up on the hull like this would make using weights generally impractical. There is absolutely no problem filling the holes with epoxy putty. The screw holes go all the way through. You use a putty knife to apply the putty to the holes and you see it squeeze out on the other side for complete hole filling.

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

    I seem to run about the same quantities as Dave does. For the first unthickened coats I prefer a roller. It's fast and there's no need to waste epoxy by leaving puddles of it here and there. A notched spreader is a good way to get the final layer of thickened goop spread quickly and evenly.
    -Dave

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

    What are you making up that requires several 4 X 8 sheets stacked up? That's a really monolithic block of wood!

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

    There's a section in the Gougeon Brothers book on estimating.
    They say 13 ft^2 per pound of mixed resin.

    What Wizbang says about clamping with drywall screws.
    Work from the middle to the edges.

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

    48 w
    x 96 l
    4608 A, in2 Area
    4608 in2 Area
    x 0.001 in thickness (t) 0.00254 cm
    4.608 in3 Volume
    Volume (10 lb/gal)
    t in3 cm3 oz qt lb
    0.001 4.608 75.5 2.6 0.2
    0.005 23 377.6 12.8 1
    0.010 46 755.1 25.5 0.8 2
    1/16" 0.0625 288 4719.5 159.6 5.0 12.5

    A 1/8" notched trowel gives a 1/16" thick glue thickness. You may also have 0.001" absorbed into the plywood that doesn't add any thickness.
    Management is the art of counting beans. Leadership is the art of making every being count. --Joe Finch

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

    The contact area is so large, you might want to use a less stressy and expensive adhesive.....the ply panels themselves dont use epoxy...

    We had a plywood hot press at the shipyard for laminating boards together, or adding veneer faces, mostly we used a resourcinal glue.

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

    Titebond 3 will be cheaper, easier and plenty strong

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

    Spirit,
    Are you lamming them into a curve or a shape or just gluing them together flat ?
    How many, just two ?
    Remember ,you can pre coat surfaces, let it go off, wash the amine blush and then do the bonding, if you are concerned with too many batches at once or things getting out of hand or the job becoming resin starved. Just an option.

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

    Drywall screws will not draw the sheets together, you need to use wood screws with the smooth non threaded shank at the top.

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

    [QUOTE=JimConlin;5704330] There's a section in the Gougeon Brothers book on estimating. They say 13 square feet per pound of mixed resin.

    Thanks Jim. I looked for but missed that excellent reference.

    Several members asked why I want to make such a thick slab. I am following Tom Hill's successful idea of using a 1.5" thick okoume plywood bottom for his Long Point skiff.
    Tom got a smooth flat bottom without frames that could withstand some pounding. I want the same, plus a very low center of gravity for a shallow experimental craft.

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

    I still think vacuum pressing will give you the best product. But if you want to use screws to apply pressure, consider pocket screws. They are flat headed so they won't dimple the surface and the shank is smooth near the head in order to draw the material together. As mentioned above, drywall screws are not so good in this application.

    Jeff

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

    Besides the aforementioned problem with drywall screws, one which can be avoided by drilling thru the top layer with a bit the same diameter as the threads after having drilled with a smaller bit into both layers, they will often snap off while being removed once they've been epoxied in, leaving you with a future rust problem.

    I use plain old electroplated pan head screws with the holes drilled as described and a packing tape backed wooden square washer under a metal washer. Rip out a strip of 1/4 or 3/8 by 1 1/2, back it for it's full length with packing tape then crosscut to whatever lengths you want. The thicker shanks of the less brittle panhead screws don't break.

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

    I did not say "drywall screw" .I said"construction screw".

    https://www.homedepot.com/p/Grip-Rit...2_rr-_-2049822

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

    In and out with this, they will not break off.The "impact" breaks the epoxy, not the screw.

    Drywall screws taken out with a regular drill, yes, that's a bad idea.

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

    I had a impact driver once, for about ten minutes, couldn’t handle the noise, gave it away.

  22. #22
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    Default Re: How much epoxy is needed to bond sheets of 3/4" marine plywood together?

    I like my Yankee, like this, for the job.


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

    Quote Originally Posted by jpatrick View Post
    I still think vacuum pressing will give you the best product. But if you want to use screws to apply pressure, consider pocket screws. They are flat headed so they won't dimple the surface and the shank is smooth near the head in order to draw the material together. As mentioned above, drywall screws are not so good in this application.

    Jeff
    I totally agree about vacuum bagging.You will get a much better job with the uniform pressure.Its still a good idea to have a couple of screws per layer to prevent the upper sheet sliding around and I sincerely hope you don't find yourself cutting into them in a subsequent operation.

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

    Quote Originally Posted by L.A Marche View Post
    I had a impact driver once, for about ten minutes, couldn’t handle the noise, gave it away.
    Ear/hearing protection is your friend. And for some, i.e. me, it is a lifeline to keeping what little hearing is left.

    Jeff

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

    Quote Originally Posted by Ian McColgin View Post
    I like my Yankee, like this, for the job.


    Gee, if you used this to drive the number of clamping screws required for epoxy gluing two 4'X8' sheets together, I reckon you'd have an awful blister on your palm, and the epoxy just might go off before you finish.

  26. #26
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    Default Re: How much epoxy is needed to bond sheets of 3/4" marine plywood together?

    Yankee might get em in ok, but it won't get em out . They will be glued in slightly.
    It's that obnoxious racket an impact driver makes that breaks the glue.
    I keep a yankee in my tote. I do not let wet epoxy anywhere near it.

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

    Quote Originally Posted by wizbang 13 View Post
    I did not say "drywall screw" .I said"construction screw".
    Screw.jpg
    https://www.homedepot.com/p/Grip-Rit...2_rr-_-2049822
    You may be thinking of fine thread drywall screws, which are crap. Coarse thread drywall screws don't usually have the self drilling tip, but you don't need it here and they do clamp a lot better than the fine thread ones.
    drywall fine.jpgPOS fine thread drywall screw.
    Quote Originally Posted by Gib Etheridge View Post
    Besides the aforementioned problem with drywall screws, one which can be avoided by drilling thru the top layer with a bit the same diameter as the threads after having drilled with a smaller bit into both layers, they will often snap off while being removed once they've been epoxied in, leaving you with a future rust problem.

    I use plain old electroplated pan head screws with the holes drilled as described and a packing tape backed wooden square washer under a metal washer. Rip out a strip of 1/4 or 3/8 by 1 1/2, back it for it's full length with packing tape then crosscut to whatever lengths you want. The thicker shanks of the less brittle panhead screws don't break.
    When you need a washer for a bugle head or flat heat to prevent splitting you might consider a cabinet screw:
    Cabinet Screw.jpg

    Quote Originally Posted by L.A Marche View Post
    I had a impact driver once, for about ten minutes, couldn’t handle the noise, gave it away.
    I haven't tried one of the oil pulse impact drivers, but they are supposed to be a lot quieter:
    https://www.popularmechanics.com/hom...ivers-quieter/
    A small group of new oil pulse impact drivers have been designed to cut down on the noise by at least 50 percent, as well as reduce vibration for the operator, all while performing at the same or higher level as their standard counterparts.
    Management is the art of counting beans. Leadership is the art of making every being count. --Joe Finch

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

    Whats wrong with clamps and cauls? Rough cut the pieces set up some horses and clamp it all up. 2x4 cauls with ply shims and C clamps.
    Use thicker shims in the middle of the sheets to account for the bow, thinner shims closer to the edges.
    No holes to fill, no hidden broken screws to hit later on.

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

    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?

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

    Drywall NAILS work a treat for tensioning skin when sewing a coaming into a skin on frame kayak, though. The large heads resist poking through the fabric, but the sharp points poke through easily.
    Just pop them in the sewing holes to hold tension as you sew around. They pop in and out easily and do little damage, so the tension and position can be adjusted and readjusted.

    Sorry for the drift.

    Peace,
    Robert

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    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?
    The Long Point Skiff is designed with a 1 1/2" thick plywood bottom and its nearly dead flat with hardly any rocker and no skeg. Theres no floor framing so the bottom is the structure. Sturdy and rugged and a tad fancier than the LYS. Id scarph the joints and half lap the sheets.

  32. #32
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    Default Re: How much epoxy is needed to bond sheets of 3/4" marine plywood together?

    Sounds like a fun project, any fiberglass or kevlar going between the layers ala Louis' Sport Dory build? You might give Jamestown Distributor's Tech Team a jingle, they possibly have your answer and the products you need. You can buy pre thickened epoxy that would cut down your working time in exchange for a few more pesos. We have had good luck with their TotaBoat THIXO and it comes in at a lower price point that Pettit Flexpoxy. TotalBoat ships free in CONUS.
    If I were doing that job I'd check into a pneumatic caulk gun, unless you have Incredible Hulk hand strength.

    Cheers
    Kent and Skipper

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

    I too would use Hydro-Tek rather than okoume. I'd roll a coat of unthickened on each sheet then use a 1/8 inch notched trowel to apply thickened with wood flour to one sheet then nail them together with silicone bronze ring nails on 8 inch centers in each direction. I'd glue up and nail the scarfs while laying up the two layers.

    If going with Hydro-Tek I'd use two layers of 5/8 (15 mm).

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

    Crikey I had not even thought of just using small anchorfast nails and leaving them in!
    Odd, cuz I've done it that way in the past.

  35. #35
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    Default Re: How much epoxy is needed to bond sheets of 3/4" marine plywood together?

    You're getting old and forgetful Bruce. Me too.

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