Glue Joint Myths

[JPG]

BUT BUT BUT the end grain 'joint' did NOT (IIUC) fail due to wood fiber failure, but rather at the glue/wood interface. This is so since the wood is so much stronger 'along' the grain and that strength exceeds the glue bond. It is when the stress is normal(orthogonal) to the end grain that wood fiber failures occur before the glue bond fails.

IF Steve really things that a butt end grain joint in a frame is adequately strong, I know of a bridge in NYC that is fer sale.

One must understand what is actually being 'proven' here. Modern(at least one) glues are stronger than most wood fiber lignin. Joints themselves are a different species(pun intended). Strength along the grain that does NOT depend upon the lignin is far greater than the strength that does depend upon the lignin.

[RFGuy]

BUT BUT BUT the end grain 'joint' did NOT (IIUC) fail due to wood fiber failure, but rather at the glue/wood interface. This is so since the wood is so much stronger 'along' the grain and that strength exceeds the glue bond. It is when the stress is normal(orthogonal) to the end grain that wood fiber failures occur before the glue bond fails.

IF Steve really things that a butt end grain joint in a frame is adequately strong, I know of a bridge in NYC that is fer sale.

One must understand what is actually being 'proven' here. Modern(at least one) glues are stronger than most wood fiber lignin. Joints themselves are a different species(pun intended). Strength along the grain that does NOT depend upon the lignin is far greater than the strength that does depend upon the lignin.

JPG,

Yes, you are right. It really comes down to the construction selected and the grain orientation. As I stated previously, the key finding for me from Patrick's video is that end grain butt joints are as strong as the glue bond itself, which for PVA glues can be quite strong. The "myth" that I think was busted is I have seen/heard all over the internet that end grain butt joints are VERY weak because the end grain will soak up all the glue like a sponge leaving a very weak glue bond. In my opinion, Patrick busted that myth. At the end of the day, I still wouldn't trust a butt joint no matter the grain orientation. I prefer a M&T, floating tenon, spline or some other mechanical means to connect the boards in addition to PVA glue. Not being considered here is longevity of the joint, i.e. how do different joints and different glues hold up over several years. As an example, I would NEVER trust a butt joint to hold up outside with sun exposure and humidity changes, but the addition of a mechanical device in between would likely extend the lifetime of the joint.

[DLB]

BUT BUT BUT the end grain 'joint' did NOT (IIUC) fail due to wood fiber failure, but rather at the glue/wood interface. This is so since the wood is so much stronger 'along' the grain and that strength exceeds the glue bond. It is when the stress is normal(orthogonal) to the end grain that wood fiber failures occur before the glue bond fails.

IF Steve really things that a butt end grain joint in a frame is adequately strong, I know of a bridge in NYC that is fer sale.

One must understand what is actually being 'proven' here. Modern(at least one) glues are stronger than most wood fiber lignin. Joints themselves are a different species(pun intended). Strength along the grain that does NOT depend upon the lignin is far greater than the strength that does depend upon the lignin.

Thank you! I have one of those finger-jointed end-grain 2 X 4's in a barn stall wall, and the horses broke it cleanly at the joint just by rubbing their necks on the stud. They could never do that on a 'real' 2 x 4. These videos prove that these joints are pretty strong. They also prove that they are not as strong as the wood without a joint because it always breaks clean at the glue joint.

- David