Joining Plywood

[Ryan]

I have a bulkhead that I want to replace. It is 53" wide and there isn't anyway I can shorten it. It is made from 1/2" thick teak veneered plywood. What is everyone's opinion as to the best way to join two pieces that make up a structural item like this? One side will be plainly visible from the cabin, but there are several ancillary items that mount to the bulkhead in it's finished state that could help mask a joint line. My limited woodworking knowledge leaves me with either a scarf or lap joint as options (neither of which I have a lot of experience doing). The "other" side of the bulkehead will be in the head, so I could possibly use another piece of wood as block and go with a butt joint. My wood working tools are fairly basic (table saw, router), but I could employ the help of a local cabinet maker if I had to. Opinions?

Ryan

[Homer]

Perhaps this is not the most efficient way to go about it, but one way to produce a stunning panel is to scarf marine ply with epoxy and cut it exactly to size. Then veneer with book-matched teak. Book-matching assures that the edges you join will have the same grain patterns. You can produce whatever width you require - even go around a corner. Veneer suppliers can fix you up with beautiful material. Buy their recommended adhesive and follow their instructions. You will need a small veneer trimmer bit for your router to trim off the edges. Put on a bunch of coats of varnish and the bulkhead will not disappoint. The process is not difficult.

[Quetzalsailor]

If the joint were closer to the centerline it would be less structural; if farther outboard, it's shorter but structural. If outboard, perhaps a butt block could be concealed in casework in the head. With determination, care, and a sharp plane, you can joint the two pieces of plywood to a very high degree of perfection. Reasonable strength across the join can be done with a plywood spline (plywood so that you get fiber crossing the joint; ideally, you'd like as much fiber crossing as there is end grain along that edge). Imperfection in cutting the dadoe or the spline can be accomodated in filled epoxy, if you can arrange to clamp the show surface of the plywood into the same plane.

Making up a scarpfed panel is certainly doable, but it's something that I've avoided. Read up in Gougeon's book as well as in numerous WoodenBoat articles. Veneering a panel is certainly doable and I've been pretty successful at it; most recently, I've reveneered the exterior of a Flying Dutchman hull using 1/16" veneer and epoxy. I achieved great long perfect fits with a block plane. I clamped using staples. (Mahogany is diffuse porous so filled staple holes are camouflaged.)

Being an amateur and without really adequate clamping methods for perfection, use thicker veneer. 1/16" is quite good; 1/32" is doable; 1/42" is beyond my skill level (gotta' have something to sand!). Vacuum bagging is not in everybody's bag of tricks and will have a tougher time pulling thick, ripply veneer down.

I've veneered in the more distant past using contact cement: works fine but it's a bit flexible (as well as unforgiving of a premature sticking!). Some of my veneer has checked because the rubber does not restrain it. Classic furniture veneering is done with hot glue, but that's not boating stuff; it's water soluble. Aliphatic resin works, given adequate fast clamping.

[Homer]

Interesting to hear of other success veneering. It is really useful and the results can be spectacular. Perhaps have a go at something less obvious than a bulkhead for the first try. I am going to do the panel on the front of my icebox with ribbon mahogany once a few other pressing jobs are completed. Vertical vacuum bagging will do the trick. This is much more fun than putting in a new holding tank.

[Hirilondë]

An 8:1 scarf of plywood using epoxy is as strong the the plywood itself. There are many stitch and glue boats out there made entirely of scarfed plywood. It doesn't matter where in the finished panel the scarf is. What you do to decorate it afterword is strictly a matter of choice.