problems bonding walnut to cherry

tom in caledonia · Post by **tom in caledonia** » Wed Aug 31, 2005 11:45 am

I was bonding walnut scupper blocks to a cherry inner gunnel last weekend (thickened West Systems epoxy and 205 hardener). A few days later I picked up the assembly and immediately heard the sound of the epoxy cracking when the piece bent. Sure enough I could remove all blocks with a bit of a pull and a putty knife. The bonds all failed at the walnut/epoxy interface. I glued freshly planed surfaces together. I may also have removed too much epoxy by clamping too hard although a uniform layer could still be seen on the cherry. Could the walnut have a natural oil residue on the surface? If so, will washing with acetone remove enough for bonding? Should the walnut also be sanded to increase the tooth? The seats hang from these things so I want a good bond. Also, the Redbird that I'm making has a fair bit of recurve on it. Anyone had any good results steam bending walnut? It would take significant force to bend the gunnels to shape without it.

Glen Smith · Post by **Glen Smith** » Wed Aug 31, 2005 12:53 pm

Here is how I would do it: Clean the wood surfaces with acetone or lacqueur thinner then sand with 80 grit to provide a bit of "tooth". Apply straight epoxy (resin & hardener) without any thickeners to both bonding surfaces a few times, until the wood will no longer absorb epoxy. Wipe off excess epoxy. Apply thickened epoxy to bonding surface and clamp lightly.

Not soaking the surfaces first will cause the wood to suck the epoxy out of the thickened mixture leaving a dry joint. Not sanding with 80 grit will leave a surface that might be too smooth for the epoxy to get a good bond. Not washing the wood first could leave oily residues or contaminants on the surface. Over-clamping will force out too much epoxy creating a weak joint.

I have not yet made canoe gunwales out of walnut so I can't comment on that except to say that if you have some spare walnut, you could try a test to see if it will steam-bend well.

tom in caledonia · Post by **tom in caledonia** » Wed Aug 31, 2005 1:25 pm

Thanks Glen. I did the unthickened epoxy on both walnut and cherry until saturated but the walnut obviously was not interested. I'll try the solvent and sanding next time. Right now, I'm off for a 7 day backpacking trip in Killarney. The canoe will have to wait a week. Yeeha!

Its Me · Post by **Its Me** » Wed Aug 31, 2005 2:21 pm

Just to let you know it can be done. I have walnut gunwales bonded to cedar scuppers and all expoxied onto the shear line of the canoe. No problem. I used thickened Raka epoxy (silca was the thickner).

http://pg.photos.yahoo.com/ph/georgetcu ... /my_photos

Post by **Patricks Dad** » Wed Aug 31, 2005 3:05 pm

Huh,,, Now you've got me worried. We built our decks out of 2 pieces of walnut with a sliver of cherry down the middle and glued them together and to the cherry gunwales with West System epoxy. Also, our yoke and seats (cherry) are attached to our gunwales using walnut dowels. I don't think any of these joints have seen any real stress yet. I hope we don't have the same problem... :praying

Bud · Post by **Bud** » Wed Aug 31, 2005 3:44 pm

I've never had a problem joining any woods with epoxy, but I always follow all the steps that Glen outlined earlier. The only thing I do differently is wipe with thinner after sanding with 80 grit.
Bud

Bill from Louisiana · Post by **Bill from Louisiana** » Wed Aug 31, 2005 8:28 pm

I have used walnut on southern pine on my Redbird with no problem. I also used stainless steel screws when I attached my inwales and left them there. Countersunk and used walnut plugs for a nice contrast with the pine. Makes for a very strong bond.

Bill

Erik, Belgium · Post by **Erik, Belgium** » Thu Sep 01, 2005 12:31 am

I do the bonding as Glen described it, the only different thing I do is soaking both bonding surfaces only once because epoxy hadn't been soaked up entirely by the wood when I did it.
I used walnut scuppers on ash gunnels (in and out) without problems on my 38SPL.
And on the Winisk I glued walnut in and outwales to a walnut sheer strip. Here I used some different product instead of thickened epoxy: I used an epoxy paste (very thick reasin) mixed with my regular epoxy hardener. I also soaked the bonding surfaces with fresh epoxy here. Both products are from the same manufacturer and in fact it 's both the same epoxy brand. This worked out very nicely, and quite easy.

I glued cherry on walnut in more then 5 paddles using PU glue, worked out fine, but I wouldn't recommend it for gunnels.

Erik, Belgium.

wilk · Post by **wilk** » Fri Sep 02, 2005 6:17 am

I am a retired owner/operator of a custom woodworking shop so have some experience on this topic that may help. There shouldnt be ANY problem with bonding cherry and walnut, the cell and grain structure is nearly identical in the two woods. There has to have been a problem in either the technique or the epoxy for it to fail so easily. Be very careful with "pre- bonding" to fill the grain. That can actually lead to a weak joint by not allowing the wood to absorb the epoxy on the final assembly. All you would end up with is a molecular bond of epoxy on epoxy when what you really want is the wood to be bonded to wood BY the epoxy.

Rick · Post by **Rick** » Fri Sep 02, 2005 7:34 am

I agree, it's really strange that the woods would separate so easily, even a minimal amount of epoxy should create a bond. Have you checked the leftover epoxy itself to see if it cured properly?

Jeff in Pembroke · Post by **Jeff in Pembroke** » Wed Sep 07, 2005 7:11 am

I put solid walnut gunnels on my Redbird. It was necessary to steam bend the ends of the outer gunnels to make the recurve profile of the stem. The gunnnels were put together with several shorter pieces or walnut, scarfed and glued with epoxy. One of the scarfed joints was in the section I steamed and the joint held with no problem (I used WEST 105/205). The ends were steamed and clamped into position and allowed to dry for a couple of days before attachment. Both the inner and outer gunnels were epoxied onto the hull with no screws or other hardware. The inner gunnels were scuppered and the ends were tapered - they were flexible enough to install without steaming. There are some pictures posted in the project directory.

Cheers,

Jeff

Post by **Patricks Dad** » Wed Sep 07, 2005 7:31 am

Jeff, I noticed a couple days ago that the picturs of your Redbird no longer show up on the your post in the Project Directories. Are the links bad?

Jeff in Pembroke · Post by **Jeff in Pembroke** » Wed Sep 07, 2005 11:13 am

Thanks for the note Randy,

I checked with my friend and his website was recently revamped - the canoe file (not really related to his business) got deleted. I called him and the file was restored. I think the pictures are working now.
BTW - I may have missed some posts - is your Redbird in the water yet? I've had three wilderness trips in mine this year so far - still love the way it paddles, especially in choppy, wavy water.

Cheers,
Jeff

Post by **Patricks Dad** » Wed Sep 07, 2005 11:17 am

Indeed they are working now. Thanks for fixing it so quickly.
Our Redbird is getting pretty close. Look for a post in the next couple weeks!