Hi all,
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?
Aidan.
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.
Bob S.
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.
Brian
Free WW software, forums and l> Hi all,
Thanks for the reply Bob.
The mortise and tenons were a great fit even if i do say so myself. :-)
Aidan
The next post made a good point about maybe being to tight and the joint was starved for glue. Also, is the poly glue out-of-date ?
Bob S.
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.
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.
Aidan
Any chance the poly got frozen?
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.
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 assembled. Regards Dave Mundt
Glassy and smooth if i remember rightly, but i did clamp up imediately after applying the glue.
Aidan.
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