Thread: Issues with edge joint - bad glue?

The other critical bit of info you haven’t mentioned is, what is the timber?

Parfix PVA. Would not be surprised if there's a fair amount of extender (flour) in it. Unfortunately it's another case of you get what you pay for.

Originally Posted by DJ’s Timber

The other critical bit of info you haven’t mentioned is, what is the timber?

Shining gum

I have used Parfix PVA for years and have seen no indication that it is second rate.

I would not be using 4 year old glue - just in case.

I bought some aquadhere exterior. I'll see how I get along with it. I don't seem to be using enough that cost is a big issue tbh.

Before I developed confidence in the tightness of my joints, I used slightly thickened epoxy as my go to glue. It's gap filling properties compensated for my deficiencies in craftsmanship.

PVA is not a gap filler so this might be an issue. The age of the glue could also be an issue. I have not had issues with gluing shining gum (aka nitens).

both Titebond and Aquadhere are good products - I don't know about Parfix. When you buy stuff from the super discounters, you will expect a high proportion to be crap, a small percentage are gems. One problem with Bunings is that they stock Good products and crap products side by side, and often their staff do not know the difference.

One thing to keep in mind with all PVA emulsion based adhesives is they are made by polymerisation to produce polymer particles of various sizes suspended in a water base. With time gravity takes effect and the particles settle leaving a thin liquid layer on top which inside a glue bottle can be very hard to see and very difficult to re-disperse. This is especially the case with imported products such as my favorite Titebond which may well be 1 year old when sold at the retail level here in Australia.
Cheers,
Paintman

Originally Posted by Carriage

I bought some aquadhere exterior. I'll see how I get along with it. I don't seem to be using enough that cost is a big issue tbh.

Aquadhere exterior should do the job.. bit messier to work with comparing to PVA.. but I never had any issues with it.. at one occasion I had 600 x 2000 x 45 board falling off the stand after being glued up.. timber cracked and split board in pretty much half length wise..but glue did not give up.. just applied glue to the crack line.. and clamped it again.. cant even see where the crack was..

Originally Posted by Prle77

Aquadhere exterior should do the job.. bit messier to work with comparing to PVA.. but I never had any issues with it.. ..

??? I thought Aquadhere was a PVA ???

Originally Posted by GraemeCook

??? I thought Aquadhere was a PVA ???

According to the Aquadhere website, Aquadhere Exterior is a PVA (it says it on the bottle).

Please post some pics of the failed joints.

Ok, big misconception on glue... A properly prepped joint is typically stronger than the surrounding wood... BUT... The glue is not stronger by itself. All of us can attest to wide glue lines failing well before the wood.

Epoxy is one of the only glues that can tolerate some gap in the joint.

Typically "glue failures" are actually jointing failures.

A few things:
*Freshly prepped wood surfaces glue much better.
*Given equal jointing quality, planed joints are considerably stronger than sanded joints...
*But... A poorly prepped planed joint will be much worse than a well prepped sanded joint.

The #1 thing in studies tends to be the joint tightness prior to glue. Every 0.1mm of extra sliding clearance makes loose wobble which turns into a broken joint.

If you have a loose joint that you need to shore up, epoxy can be your friend. You need to use the good structural stuff used by sailboat guys, like West Systems. The wood still has to be carefully prepped immediately prior, and the epoxy prepared properly and applied to whet all the wood surfaces.

Unfortunately I didn't take any photos and have already reglued the joint.

I would have thought that I should have had good contact somewhere, it being an edge joint. However I don't recall finding any spot that looked like timber failure. Also, from some unrelated reading, I don't think any gap would have been bigger than what a spring joint would have. I could be wrong there though, both on memory of what I had and on how spring joints work.

I also can't recall if/how much I adjusted the fit when I was cleaning the dried glue off the edge of the boards

Originally Posted by Carriage

... I would have thought that I should have had good contact somewhere, it being an edge joint. However I don't recall finding any spot that looked like timber failure. ...

Having contact somewhere is not enough. With most glues you must have contact virtually everywhere. The exceptions are the gap filling glues which essentially means epoxy.

A tiny bit of glue will fail before the timber; a moderate amount of glue will tear the timber out.

But if the glue itself is defective - long out of date or stored too hot - then it ain't glue anymore.

The questions that you are asking are all good; we have all been there ! The trick is to try not to repaet the same stuff ups too many times.

Re-gluing any joint is a risk. Glue works by bonding with the fiber of the wood. When a glue joint fails the original glue remains and adding new glue simply does not penetrate the wood blocked by the original glue. The joint will always be weak.
Without doubt this is a topic that could roll on forever but here are some Youtube links that might shed some light on the great end grain glue debate.
calabrese55

Glue Myths: 1. End grain https://www.youtube.com/watch?v=m7HxBa9WVis

End Grain Glue Myths | You May Have Misunderstood

End Grain Glue Myths | You May Have Misunderstood - YouTube

A misunderstanding of the end-grain glue "myth" video?

https://www.youtube.com/watch?v=dwLWmoGh59g


in general
https://www.youtube.com/results?sear...ng+glue+joints