Which glue for solid transom

[Paul Eaton]

I am about to glue up my transom - solid wood (bubinga - African rosewood) 1"thick 3 planks. I was planning on using West System epoxy as I am familiar with it and never had problems. However I have never edge glued panels before. (My Penobscot 14 didn't need any)

I have planed the planks up and they are a nice fit. I am concerned that if I clamp up the panels because of the good fit I will end up with a glue starved joint. I was going to spline the edges to make fitting easier which may help.

I also have some Aerodux resorcinol glue which I have never used before but, I have been told, is an ideal glue in this situation.

Am I worrying about nothing in which case I would go with what I know or should I use the resorcinol? Any advice out there?

[Tom Robb]

Wellwood plastic resin glue works just fine. Cheap, water clean-up, lo-tech. What more can one ask?

[Dave Gray]

I have no experience but based upon what I have read drift pins and resorcinal are the best way to go. I think Greg Rossels (sp?) book discusses this and there may be something in the FAQ, although it is much reduced from what it used to be....

[Thorne]

I'd ask Bob Smalser about the Aerodux resorcinol, but as long as you've got the required clamping pressure and temperature (70 + degrees??) it sure sounds like the way to go. How oily is the rosewood?

[Paul Eaton]

Bubinga isn't oily like teak.

http://www2.fpl.fs.fed.us/TechSheets/Chudnoff/African/htmlDocs_africa/Guibourtiaspp.html

Comes up very nicely bright.

[Bob Smalser]

...solid wood (bubinga - African rosewood) 1"thick 3 planks. I was planning on using West System epoxy as I am familiar with it and never had problems. However I have never edge glued panels before....spline the edges.....



I'm afraid I don't have any experience with Bubinga except piddling around with a few turning squares of it....I don't know how it glues. The USDA says it "glues well", and that may mean epoxy done by the recommended sequence of unthickened left to stand for 5-10 minutes followed by thickened and light clamping pressure...just enough to make the boards touch...will probably work fine.

I'd use resorcinol to be sure, however....or urea resin (Weldwood, DAP etc) if a purple glue line is a problem. One reason is these glues have been proven in marine use longer than epoxy , but my main reason is clamping pressure...both these glues like a good bit of it. That means I can lay them up with no fear of starving the joint, which is very easy to do on large layups of large pieces of very hard wood using epoxy. Probably the majority of glue joint failures relate to incorrect clamping pressure, and if you don't have hundreds of successful layups behind you, you won't go wrong with these oldies providing you have 70 degrees or warmer temperatures. Use a heat blanket if in doubt, as temperature with these is critical compared to epoxy. Use only resorcinol for glue joints below the waterline, however.

And by all means drift the transom after layup, bedding the drifts in bedding compound or red lead instead of more glue. Should the transom ever be damaged in use, the drifts will hold it together....and they also serve to distribute the various forces on the transom to all three boards comprising it, not just one or two. For a 1" transom I'd probably be looking at 4 drifts of 3/8" diameter.

There's also no need for splines in a simple layup of three flat boards, square edges are just as strong and just as easy to line up on your bar clamps using a rubber mallet. With splines there is greater danger of voids and subsequent rot pockets. Insure your clamps are clean and on a dead-flat surface....use bar instead of pipe clamps which bend under pressure....and keep your layup both flat on the bars and the edges aligned using your fingers to feel and the mallet to adjust as you torque down on the clamps. Then monitor the flatness of your assembly for the first few hours of curing do make sure nothing goes awry. At least one clamp on top of the layup for every two on the bottom, and you'll have fewer problems than cutting and fitting splines.

But when you do need splines, then quarter-inch marine plywood for the splines and a matching piloted slotting cutter for the router are the cat's meow, as unlike a table saw, they follow any irregularities in the board perfectly. Route your slots from both the top and bottom of the board for perfect centering of the slot.