Scafing Glue

Discussion in 'Wooden Boat Building and Restoration' started by mugsman, Feb 12, 2012.

  1. mugsman
    Joined: Feb 2012
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    mugsman Junior Member

    Anyone try Gorilla Glue on scarf joints or is epoxy still the best?
  2. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Polyurethane adhesives, such as Gorilla Glue (and others) have been well tried. They work well within their requirements and limitations. Adhesive choices tend to be application based. On wood, it's difficult to beat epoxy for several reasons.
  3. Nick.K
    Joined: May 2011
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    Nick.K Senior Member

    Polyurethane isn't a good choice for a scarf,
    Firstly as it expands it tends to push the surfaces apart and since scarfs often have a lot of surface area this makes the clamping difficult.
    Second, scarfs are difficult to cut completely tight and in open joints, polyurethane will harden as foam which has very little strength.
  4. troy2000
    Joined: Nov 2009
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    troy2000 Senior Member

    Summer before last I spliced 1x12 pine boards for the sides of a flat bottomed canoe, and 3/8" plywood for the bottom, using Gorilla glue. The boat goes in the water for two or three days at a time. In between it sets upside down on blocks, baking in the desert sun. The scarfs are still completely solid.

    Of course, I cut tight joints to begin with. And I obtained clamping pressure by laying cleats over the joints, and running deck screws through the cleats and the joints, right into the wood work table.

    The biggest problem with Gorilla glue seems to be that people use too much of it. They figure if a little is good, more must be better. It ain't necessarily so....

    Follow directions carefully. Make sure you have tight joints; apply a thin layer to one surface; and dampen the other surface lightly with water. If you get anything beyond minimal squeeze-out when you apply clamping pressure, you're using too much glue.

    I've also used Gorilla glue successfully on cracked rifle stocks by injecting it into the cracks with a hypodermic, and applying pressure by tightly wrapping the stock in strips of inner tube.
  5. Collin
    Joined: Nov 2011
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    Collin Senior Member

    1. Scarfs aren't hard to do well. You shouldn't need to have to rely on gap filling to save you. A jack plane creates very flat scarfs.

    2. Gorilla glue sucks. The joints have failed several times for me. The last thing I would use it for is an application that's under a lot of stress and where it failing would leave you in a bad spot. The joints aren't as strong from day 1 and just go downhill from there. If you're laminating two pieces of wood together, it'll probably hold alright, but I wouldn't use it for the scarfs.

    3. Titebond 3 is a good choice for scarfs for a small boat that you don't expect to last forever. It's very strong, flexible and waterpoof.
  6. johneck
    Joined: Nov 2011
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    johneck Senior Member

    Why wouldn't you use epoxy? It is cheaper, easier to work with, more water resistant, soaks into the wood better, is stronger for gap filling. Am I missing something?
  7. sean-nós
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    sean-nós Senior Member

  8. michael pierzga
    Joined: Dec 2008
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    michael pierzga Senior Member

    Some people cant work with epoxy due to allergies.

    For bright finished joints some cabinetmakers don't like the dark glue line epoxy leaves.

    High clamping pressure resin starves epoxy joints.
  9. troy2000
    Joined: Nov 2009
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    troy2000 Senior Member

    If your Gorilla glue joints are failing, it's because you're doing something wrong. And it seems the mistake made by most people is using too much glue, and/or expecting it to be gap-filling. See my post #4 above....
  10. Collin
    Joined: Nov 2011
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    Collin Senior Member

    I could give you examples, but it would be better if you tested it yourself. Gorilla glue looks good when you first use it, the problems come later while it's in use for a while. The problem isn't about adding water to the joint or using too much of the glue, it's the glue itself-not the application of it.

    Scarf some wood together with Gorilla glue and glue some scarfs with Titebond 3 or something similar.

    Now flex it, brace one end on the floor and whack the other end with a hammer, flex it some more. Do a few cycles of that and test the joints.

    You'll see that the Gorilla glue will fail at the glue line. Why? It seems to have to do with just how brittle the glue is. The Titebond has enough give to it and the polyurethane adhesives just can't cope. If the joint doesn't have to flex or there's no chance of concussion, you're fine...but what doesn't flex and get hit in a boat?

    If you e-mail Frankin, I'm sure they'll tell you the same.

    I await the results.
  11. tunnels

    tunnels Previous Member

    Shame on you !! how can you even think such a thing !! Gorila glue is not good enough !! end of story there is not more !!:mad:
  12. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    All glues (natural) and adhesives (man made) have good and bad points to consider about them. When comparing to epoxy, it's extremely difficult for any to fully stack up, mostly because epoxy is so much more then just a bonding agent.

    I dislike the foaming PU's because they can admit moisture into the open cells along the edges of the joint, which in northern climates will freeze and test the glue line, repeatedly over the course of a single winter. In more temperate locations these same cells harbor little beasties and other issues. These adhesives require good joint fits, lots of clamping pressure and, though better then some are sensitive to bonding environment conditions.

    This is why epoxy has taken the industry by storm. It needs minimal clamping pressure, doesn't need tight joints, can be used as a moisture vapor barrier, can be had in thousands of application specific formulations, etc., etc., etc.

    I've done some testing with PVA's and PU's in an attempt to use these to bond sheathings. Some PVA's have shown a bit of usefulness, but not nearly as much so as epoxy.

    Ultimately, you have to make a decision, based on your own testing (if necessary), publicized vendor information and general conscientious comparison.
  13. cthippo
    Joined: Sep 2010
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    cthippo Senior Member

    I'm a big fan of Gorilla and have used it extensively in the boats I've built especially for stripping / scarfing. I use epoxy as a coating, with or without a fiber component, but for assembly I use mostly gorilla glue or, if it really really has to last, 3M 5200. I use Titebond 2 (TB3 isn't readily available around here) for certain applications such as laminating cockpit rings where the expansion of the GG isn't desirable.

    My take on it, and I'm sure some will disagree, is that if you're going to coat the finished piece in epoxy, then it doesn't matter that much what glue you use.

    To each their own, I suppose.
  14. ancient kayaker
    Joined: Aug 2006
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    ancient kayaker aka Terry Haines

    It's hard to understand Gorilla Glue's attraction - it's expensive, the foaming action is a nuisance, it's not very strong and tends to set in the bottle if there is much humidity around. The only advantage it has is the stuff that spills out of the joint expands to a weak foam that is easy to remove.

    I personally don't like epoxy for scarf joints, it's a good lubricant so the pieces tend to slide apart and it takes too long to set up, which ties up my clamps especially if I am building a strip-built boat with dozens of scarfs. Being a spoiled brat I also detest the measuring and mixing.

    IMHO Titebond III is a good choice for scarfing - it can be moved with clamps in a minute or two once the excess water is absorbed into the wood when it stops being slippery, and the joint can be unclamped in an hour or less, releasing the clamps for other jobs. I read that nothing much sticks to dried TB3 if a joint breaks which is supposed to make repairs difficult, but I have never seen dried glue exposed by a break because it's always been the wood that failed - even with oak.

    You need a decent joint fit for TB3. After a lot of experimenting I now use a bench sander for small pieces, it is accurate and fast. I use a plane for the bigger stuff; if I get a lousy fit despite my efforts I mix up some epoxy and take the day off . . .

    As far as the water resistance of TB3 is concerned, I don't believe the "waterproof" claims. If water can reach at it, it softens. Unlike most glues when it dries out it recovers most or all of its strength, but while soft it will let go easily. But it needs a lot of soaking for that to happen; for any boat that is dry moored a decent paint job will protect it. Epoxy sealing is only needed for a boat left in the water and that should be built with epoxy throughout IMHO . . .

  15. tunnels

    tunnels Previous Member

    Fast epoxy in combination with your standard epoxy !! A small amount on the centre of the join and the slower at the ends . if you are just doing 1 or 2 joins then clap lightly no more slide
    doing a bigger job usually clamp 6 or 8 0r more at the same time on a flat surface laid side ways and a layer of plasitc between each one .And dont have all the joins in the same place mix them up a little ! You shouldnt clamp really heard any way just a light clamp is all thats needed . Gorilla is a waste of time and as for water based forget it dosnt have any place in any part of a boat . :rolleyes:
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