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Permalink Reply by Rick Newman on December 14, 2010 at 8:12am

Jerry, thanks for sharing the article.  This will save me some time, mess and money on my build. I like seeing test results like this.

 

Rick Newman

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Permalink Reply by Jordan Davis on December 14, 2010 at 11:27am

This is awesome info for sure.  It raises some questions though...Although we know that the Type I PVA used in the article states it is "waterproof" we also know it is not submersible or to be used below the waterline.  My question is then this, if we are going for the best and strongest joints on frames and chines, why aren't we using this type of adhesive?  In my experience I wouldn't say that PVA is less flexible than epoxy, but probably of equal value in that respect.  On the other hand, we know that 5200 or Sika is far flexible than either of those.  This opens a whole can of worms....Thoughts?  I hope to hear from some of the experts here on this one...

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Permalink Reply by John Greenleaf on December 14, 2010 at 1:58pm

IMO, there's no silver bullet. For furniture making, sure, go with PVA - cheap and good; but this is a very static situation. With boats which experience water, dynamic movements, gaps in joints or fillets etc. things change and there are many possibilities. I used all three in my build: PVA, epoxy, and 5200 (not to mention a polysulfide for the chine caps). It all depended on the circumstances. and they're all good when used for the correct application. BTW, Great article (came across it awhile back) -one thing the article does not mention though: clean up (especially the 5200). That in and of itself can be a game changer for some folks.  

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Permalink Reply by Jerry Thompson on December 14, 2010 at 2:27pm

I wonder if PVA, ie. Titebond III isn't as good as epoxy for bonding scarf joints?  The thing won't be constantly submersed. I know that my boat will be in the water for at most a day at a time, then will rest for at least a week or two,  and if the joint is stronger than the wood and water resistant and coated with paint or varnish. What the heck?? I guess you roll the dice and see. So, my thoughts are, Titebond III from the chine up and 3M 5200 from the chine down (bearing in mind that the roughest water I will ever see is the Green from the Dam down to Little Hole and possibly the Big Horn below Yellow Tail Dam or the miracle Mile on the North Platte). Any pros or Cons???

 

Jerry

 

 

 

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Permalink Reply by lhedrick on December 14, 2010 at 4:56pm

End grain glue ups are a problem for PVA glue.  I would stick with epoxy for plywood scarf joints.  Epoxy only requires contact pressure.  PVA needs tight clamp pressure.

 

If you are going to try end grain glue ups with PVA III, do it on test stock first.  I my experience in working on some picture framing in the last few weeks PVA won't hold on end grain.  On the frames I built it held the joint together well enough to cut slots and insert corner splines.  

 

It took very a very small hit to brake a 45 degree frame bond.  The is the same type of end grain joint which we would use on a gunwale scarf.

 

I have yet to try gluing some stock and putting them in water to see what happens.

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Permalink Reply by AJ DeRosa on December 14, 2010 at 3:03pm

John is right on in his reply.  The dynamic forces at work on a boat, even one that floats on easy flowing water, are far different than what is expected of a fine table or chair.  Just loading and unloading the boat from the trailer will stress the joints.  Having restored many old boats from the 50's and 60's it is easy to see that many of the frame joints are void of the adhesives used in those days and are now held together by the mechanical fasteners alone.  It will take many more years to see what happens to our modern epoxies and polyurethane marine adhesives when they have seen 40+ years of use but my money is on the new goo as opposed to the furniture builders glues.  How many of us have a favorite old chair that has sucumbed to using it's two back legs as a rocker.  Usually it is a failure in the glue regardless of the craftmanship of the joint.  The article brings some very interesting results but fails to address joinery that we deal with in framed boats.  Just add water for many years and those results might not look the same.

I did enjoy the article and it will bring some lively discussion.  After all, that's why we come here.

 

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Permalink Reply by Randy Dersham on December 14, 2010 at 4:35pm

Completely agree A.J.  I believe there was a follow up article to this one that included a test by soaking the joints in water.  The PVA "waterproof" glue failed at an alarming rate.   We should try to find that sister article.  I believe it was about one year later.

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Permalink Reply by Eric Loudenslager on December 15, 2010 at 8:05am

Titebond (PVA) glues are usually not recommended for bent-lamination construction in woodworking...search for other articles at Finewoodworking Mag on bent-lamination methods.  The PVA glues remain too elastic when put under such stress.

 

This would be the type of stress found within a scarf joint on a side panel that was bent around frames or a strong-back.

 

Threads at various wood boat building forums have generally been cautious about using PVA for scarf joints.

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