Contribution of glue used to stiffness of laminated timber

[Michael Rogers]

I'm laminating Douglas fir stripwood to make spars (a yard and a boom), each 8  1/2ft long, for my current build project which is a Swallowboats Trouper 12 hull with junk rig. Lightness and stiffness are the priority properties for the spars (the mast will be CF). Glues I could use are epoxy, Balcotan (I've got an unused bottle) or Collano Semparoc 60 (which I understand is replacing Balcotan). Does the glue I use contribute to the strength and stiffness of the finished laminate? The Balcotan or CS60 are easier to use, and I guess work out cheaper too.

[David Bewick]

Michael,

Whichever glue system you use, the objective will be to leave just a thin film of glue holding the laminations together.  Apart from holding the various components together in whatever shape you put them in (in your case, a straight spar), I can't see that the glue layer itself will make any appreciable contribution to the strength and stiffness of the construction.  Personally, I always use a PU glue instead of epoxy if I can get away with it and I have used Balcotan successfully for glueing up spars.

I hope this helps,

David.

[Timmo]

Confess I've used Screwfix cheap "Joiners Mate" PU glue for the mast and spars I made for my canoe. 

Birdsmouth construction, 8 pieces per spar only 3-4mm thick for the glue line so the glue line is important though stresses and strains are limited by the size of the rig. So far they have held up fine. 

Used same glue for paddles, same result. Would be interested in any direct comparison between PU glues to demonstrate what the more expensive stuff does better.

PU us so much kinder on tools, if there's no big 'gap filling' needed I'd use it out of preference.

Tim.

On 10 Oct 2011, at 18:46, David Bewick [via UK HBBR Forum] wrote:

Michael,

Whichever glue system you use, the objective will be to leave just a thin film of glue holding the laminations together.  Apart from holding the various components together in whatever shape you put them in (in your case, a straight spar), I can't see that the glue layer itself will make any appreciable contribution to the strength and stiffness of the construction.  Personally, I always use a PU glue instead of epoxy if I can get away with it and I have used Balcotan successfully for glueing up spars.

I hope this helps,

David.

---

If you reply to this email, your message will be added to the discussion below:

http://uk-hbbr-forum.967333.n3.nabble.com/Contribution-of-glue-used-to-stiffness-of-laminated-timber-tp3410088p3410227.html

To unsubscribe from UK HBBR Forum, click here.