Epoxy glued scarfes

Quick question ....

Lots of build guides recommend using epoxy as a method of gluing scarf joints when making up panels or for lengthening gunwales, etc...

Is this because thats "how its been done" for the past few decades ?

Is there any reason not to use something stronger, like titebond or gorilla wood glue ?


9 replies:

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RE: Epoxy glued scarfes

Tony-Nic,

Probably, because epoxy has been proven to work for that application and is stronger than the wood it's bonding. Even if you were certain that tightbond or gorilla glue is stronger, it will not make the overall structure stronger.  Do you want to discover that environmental conditions might lead to its failure or that you've compromised the structure's strength by shifting the stress or failure points?

Call me old-fashioned, but I'm reluctant to experiment with something upon which my life might depend --- unless the upside is extremely high.

Cheers,

Dick

RE: Epoxy glued scarfes

 Hi Tony,

  PVA glue (Titebond) is not at all suited to end grain applications like scarfs. Gorilla glue ditto. As good as it is at some things, it's miserable stuff for woodworking. It foams up and makes ugly yellow squeezeout. Both glues require high clamping forces and very tight joinery to achieve the best bond.


Thickened epoxy is stronger than both and achieves full strength without heavy clamping. Plus it works at full strength on end grain and even gappy joints. For end grain situations I saturate the gluing area with unthickened so it wicks into the fibers, then follow with thickened. Cab-o-cil + epoxy is super strong glue.


We used Titebond III to edge glue strips in a strip built kayak and the glue lines have discolored under the epoxy.

Cheers,

ev

 

 

RE: Epoxy glued scarfes

Yes, I used resorcinal-formaldahyde glue for scarfs. It discolored the wood. It was a mix. If not careful the glue would be grainy and not stick if too dry. It would often set too early.   But why would you want too?  Epoxy is easier to mix, has good pot time, and matches all those other joints in the boat.    

RE: Epoxy glued scarfes

   Thanks very much for all your replies, most appreciated.

Its not so much that I want to use an alternate to epoxy, just simply curious.

The Gorilla glue would have been their wood glue (non foaming) which I use on all exterior projects - never had a joint fail, hence part of my question.

I'm perfectly happy - and indeed intend - to use epoxy, but I'm a curious sort, so to know is to understand.

Thanks all for your courtesy - I know that asking non-standard questions on some forums can lead to heated replies by some ...... akin to "why would you want to use a round wheel when we've been using square ones for all these years" :)

Enjoy your weekends

RE: Epoxy glued scarfes

 I don't consider a scarf to be end grain (but do precoat or butter both sides), and epoxy doesn't actually work on real end grain much better than other glues. It's strong point is low pressure and gap filling. For hand scarfed ply, it's super helpful since pressure and perfect joints are difficult. For scarfed sticks, especially if machine-cut (with a jig on a table saw, for instance), I use woodworking glue all the time, since it's easy to firmly clamp and it dries (enough) within an hour so I can get on with shaping and installing. 

RE: Epoxy glued scarfes

   Thank you for your reply nemochad - very interesting - really appreciate your reply

 

RE: Epoxy glued scarfes

I checke a number of Titebond wood glue and the labels state they are not for structural glueing and not for use below the waterline. Since these are both requried for a kayak or other watercraft, I would not use them in building a boarr or accessories. Even if one does not think an item will be immersed in water for a a long time, I would not risk it.

If water were to get under the expoxy it could migrate to the wood glue and cause a failure of the joint. You might try contacting the manufacturer and see what he has to say about using his product in a watercraft.

 

 

   

RE: Epoxy glued scarfes

   I am undecided yet which recourse to take so I'm going to experiment between scarves and puzzle (finger) joints

It will be interesting to see the pro's & cons of each including : ease, strength, alignment, looks, ridgidity, etc.....

RE: Epoxy glued scarfes

Tony,

I think that you'll find that properly (epoxy) glued scarfs and puzzle joints are both stronger that the wood/plywood that they join. Regular planed edges for scarfing plywood sheets are expensive to manufacture for kit vendors and prone to shipping damage, so were usally left to the builder to make. Puzzle joints are well suited to the CNC equipment used today and save the builder time and labor.

Having built with both, I prefer the puzzle joints as they are pre-cut and easier to align properly. If I were building from plans, I might plane my own scarfs or buy pre-cut puzzle jointed plywood sheets from CLC, depending on the plans. Puzzle joints are not applicable to solid timber where scarfs can be either planed or cut.

Cheers,

Dick

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