Thread: Advice for Gluing up timber

When ever I am working with spotted gum I use acetone to wipe down prior to glueing.

thanks Cava

What glue were you using?

i always use Titebond3 for chopping boards.

Yep Titebond 3

I prefer polyurethane for laminating; it's not affected by oily timbers and the join never creeps

Originally Posted by elanjacobs

I prefer polyurethane for laminating; it's not affected by oily timbers and the join never creeps

Any particular brand Elan?

We used Timbatech (PU15 and PU60) at work and never had any delamination issues.

Thanks heaps for that Elan. Would you still wipe it down with acetone before gluing. Or you'd just glue it.

Thanks!

Acetone on oily timbers is a good idea.

Originally Posted by Bernard Zhang

Or should I not worry about that and make sure there is enough glue and clamping force.

I trust that you're aware that there is such a thing as too much clamping force? It'll squeeze the glue out, leaving you a dry joint that will fail over time.

In many cases you don't need clamps at all...

If you used a roll of Clingwrap (or similar) to protect your bench, glued both faces of a joint and then simply rubbed the faces together until the glue went "tacky" and started to grab, you could have done away with them altogether.

Just glue it. It will foam up as it sets, so it's a good idea to put some plastic down on your work bench (glad wrap will do fine) and don't get it on your clothes because it does not come out of fabric. Ever.

The number on the glue is the minimum clamp time in minutes, but we'd usually leave it in 3-4 times that unless we had a lot to do; one hour for PU15 and 3-4 hours for PU60 is stacks. Full cure is 24 hours

I'll put in 5c worth. The primary reason for failure is that the surfaces to be glued together are not appropriately jointed, i.e., they are not flat. One test you should do is that if you can see daylight while holding the two pieces together with your hands, then you need to get the edges straight. The second reason is the type of glue and cleanliness of the surfaces. During winter, Titebond 3 might not set all that well. Try clamp your workpiece evenly and bring them indoors, and leave it overnight. Polyurethane doesn't suffer that temperature problem to the same degree, but it needs good clamping pressure. I have never had glue joints failed because of too much pressure myself.

Originally Posted by justonething

....... I have never had glue joints failed because of too much pressure myself.....

I've often read of "starved joints" due to excess clamping pressure. I guess it's theoretically possible to squeeze out most of the glue from a join, but not sure you could squeeze out everything. The joint strength increases as the glue thickness decreases (within limits), so squeezing out most of the glue could actually increase joint strength, other factors being equal.

Rational cures come from accurate diagnosis - there are many reasons why joints fail. Putting cutting boards in the dishwasher, as some of my offspring insist on doing, is a great recipe for de-lamination, whatever glue is used & however well the joints are made!

I would suggest that failure associated with heavy clamping pressure is likely due not to squeezing out the glue per se, but because of the reason for the heavy clamping being a poorly-made join. If you don't get nice, even squeeze-out with just a little pressure, it's likely your jointing technique needs a bit of work. If you have to clamp heavily to close parts of the join, when the clamps are taken off, there is likely to be excessive tension at those points. If that is close to, or exceeds the tensile strength of wood or glue, failure is inevitable. All PVA glues are prone to creep, furthermore they are 'thermo-plastic', i.e., they soften more at higher temperatures making them more likely to creep or fail. Titebond 3 is claimed to be the best of the batch in this regard, but I wouldn't trust it entirely. PU glues are reputed to be less prone to creep, and I can vouch that hide glue is too, but of course it remains water soluble & not suitable for anything potentially exposed to moisture, like cutting boards.

Another common cause of the ends of joints failing on table tops etc., is from using wood with a higher moisture content than it should be. Even if finished immediately, the ends dry more quickly & shrink, which may stress the glue or wood to the failure point. This will be more likely where you have large seasonal temperature & humidity swings.

If your edges are well prepared, it should take very little pressure to get even squeeze-out along the entire length of the join (top & bottom). You can, as Skew says, make "rubbed joints" which need no clamping at all. Instrument makers do this all the time, and I often do it when glueing up thin panels, but I've only managed it successfully with hot hide glue. I've read where others have done it using PVA type glues, but it didn't work for me when I tried it.

Glues work at the molecular level, which is orders of magnitude less than the length of light rays - in other words, if you can see daylight between your boards when you hold them up to the light, then the gap is certainly too large....

Cheers,

It is immensely strong, can withstand prolonged immersion in salt and fresh water, does not soften in high heat (or become brittle in low temperatures). Has proven its long term effectiveness many times over. It is chemically resistant to acids, solvents and oils, and resistant to Uv degradation. It can glue difficult and oily woods. It is harder, slightly stronger and more permanent than epoxy.

It is a two part system with a reddish liquid resin and a brown powder hardener, with an unmixed shelf life of about 3 years.

The mixed pot life is temperature dependent, but about 1hr - 1.5hrs at 25C, increasing as it gets colder (and decreasing in hot weather)

Clamping time at 25C is about 6hrs.

Resorcinol is what outdoor structural timber like glulam uses, and I suspect commercial butcher block counterpoise also use it.

Resorcinol is complete overkill for something like this and, IMO, has more drawbacks than benefits compared to PU for furniture and other small pieces.

It leaves a dark glue line, requires accurate mixing, has a much longer cure time and has more health hazards (in the unmixed/uncured state).

As a test, we left a sample glued with polyurethane in a bucket of water for a few weeks with no detectable glue failure. If your cutting board needs to do better than that, it might be time to buy a plastic one...

Unless you're building bridges or boats, I see no good case for resorcinol or any other formaldehyde based glue in the home shop.