Can plywood be successfully butt glued?

harpone

New User
Harpone
I have a small project (old pattern called a book house) I am making for grandchildren's school's annual fundraising The plan called for the back to be piece of 3/4" plywood approximately 13"x13". I have LOTS of plywood cutoffs courtesy of a local contractor's cabinetmaker but nothing the right side. I can easily butt glue two pieces together to get the right dimension but will it hold? Would backing the glue joint with a piece of wood work?
 

Newboy

George
User
A scarf joint is what you want. That’s what you use for plywood boats.


Sent from my iPhone using Tapatalk Pro
 

Brantnative

Jeff
Corporate Member
13 x 13 is pretty small and the application doesn't sound like it needs a lot of strength. I've used biscuits for a similar project as Mike suggested. Mostly to keep things in alignment though, not for strength.
 

drw

Donn
Corporate Member
While I am not positive, I think the scarf joint Newboy mentioned would mate the two boards along 45 degree edges (think in terms of a french cleat).
 

shawn

shawn
Senior User
I,ve edge glued fairly large pieces of ply without issue except getting a consistently flush surface. The thickness of ply can vary a little so you wind up burning through the veneer when sanding.
 

Rwe2156

DrBob
Senior User
The alternating plys that run parallel to the edge will glue together, but the end grain layers will not. Glueing on a backing strip will work. I've done this various times for backs of book shelves, etc when I was in a pinch and didn't feel like driving to lumber depot.

So my answer is yes, so long as you keep the plys matching up, you will probably be surprised at how well it works.
 

Jeff

Jeff
Corporate Member
+1 to gluing on a back strip. The bookhouse is a small, simple project that's not going to have a lot of stresses while it's in use so don't over-engineer it.



185303
 

Gofor

Mark
Corporate Member
A true scarf joint is a ratio of 8:1 width to thickness. Therefore, for 3/4" ply, the pieces would overlap 6 inches. Typically in ply you would stair step the overlap at each ply. That produces a joint that is as strong as the original wood while maintaining the flexibility. Overkill for this purpose IMHO, and a 45 degree end mating of ply wouldn't give much more strength than a basic butt joint. Personally I would probably go with biscuits, or a 1"- 1 1/2" half lap, with biscuits being the easiest and the half lap being the stronger of the two. Another option would be a spline.
 
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harpone

New User
Harpone
Thanks for all the ideas. I had to look up what a scarf joint is: another learning experience for a novice woodwoker!:) I haven't considered buying a suitable piece of plywood because (1) I am trying to use up what I have in stock and (2) I am cheap. I don't think I have the tools to cut an effective scarf joint for gluing. I can probably get a friend to biscuit join (I do not have a biscuit cutter or appropriate router bit) . Glueing on a back strip would be easy.: how wide would the strip have to be? One last question: would a shiplap joint be satisfactory? I think I could do that on the Bosch router table I just got.
 

Jerry C

New User
Jerry
A plywood glued joint works well. Getting the grain to match can be a problem. Even Norm Abrams used a glued plywood joint on New Yankee Workshop.
 

shawn

shawn
Senior User
Try edge gluing a sample piece. I think you will be quite satisfied with the result.
 

red

Papa Red
Red
Senior User
Biscuits will work fine or you could use a spline. Either are great options.

Red
 

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