Just bought a bottle of the titebond "foaming" polyurethane glue and the
first two projects (mortise and tenon joints) have just "broken" apart with
a slight tap.
I am aware that one surface should be damp. I am guessing that I wasn't damp
enough. How damp is damp?
Damp is just a slight enough moisture to help the poly cure. I doubt that
was the problem if a slight tap broke them apart. More likely the joint was
not as tight fitting as it should have been and perhaps you were thinking
that the poly is a gap filing glue? Its not and the web the foam makes as
it dries is very weak.
Clean it off and use some epoxy glue if you need to fill a gap, or add some
"shim" material to the cheeks then re-mill them to have a nice firm fit in
the mortise. Be sure the mortise walls are clean and flat and are parallel
to the tennon cheeks.
If it foamed, there was enough moisture. I would check that you had a
tight enough joint, or that the opposite wasn't true - that the joint
was too tight and became glue starved.
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Aidan Place wrote:
Thanks for the replys,
I am confused now. At first I also thought that perhaps glue starvation was
it, but the joints are a firm hand push fit. Also i reglued the joints with
PVA this afternoon and they are solid as a rock.
Its very cold and damp here today, perhaps thats something to do with it.
Greetings and Salutations...
On Wed, 26 Nov 2003 21:52:48 -0000, "Aidan Place"
Perhaps not. I have found from experience that Polyurethane
glues CAN be fairly brittle. That is good, in that they are
sandable and will not mess up your paper. That is bad, in that
they do not survive impact.
Another bit of information that I did not see whas
how the joint looked when you took it apart. Did the layer
of glue seem "foamy", or was there just a little foam, and
most of it was glassy and smooth? In the latter case, the
glue might have "skinned over" before the joint was
Theoretically the moisture in the wood alone should be enough to allow the
wood to cure. Misting one side just kind of helps the cure along.
Assuming the glue was good and you know it if it wasn't, it'd be somewhere
between Jell-O and rock, the fault has to pretty much lie in joint
construction, glue application, or clamping. Don't like the stuff much
myself but, to give the devil his due, it does make for a strong joint.
The glue could be old and might have been sitting on the shelf for a long
time. My favorite local hardware store was a great place to get things
(before the BORG assimilated them) but I would never buy glue there because
I knew that it sat on the shelf way too long.
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