Glue Test on Baltic Birch

[LelandCrooks]

Several years ago when I first started on this I tested glues. PL, Liquid Nails, epoxy, Tite bond II. Butt glued an upright board, screwed it to the bench, attached a 250lb pull type scale and started pulling. I don't remember the numbers, but PL was so superior I've never tried anything else. Epoxy was the closest.

The trick with the PL is it has a bit of give. All the others go snap. PL just kind of tears loose, with utter destruction of the plywood. Which makes sense, because it's original purpose is underlayment on floors. You want that bit of give, it prevents squeaks.

[MissileCrisis]

IF the joinery is very tight and if the cab is a SLA/TLAH you can sometimes get away with wood glue for intricate pieces like baffles and edges that show as it is easier to tidy up. That being said, I will never use anything but PL on a subwoofer/PA.

[msprague]

Good discussion and I've learned a thing or two.

I have added a new test just with Titebond II and Locktite PL Premium. I let both joints cure for 7 days.
This is just a small 1" butt joint so it would break within the limits of my digital scale.
PL break point = 6.7 LBS - had a bit of give before it broke but did not tear out any wood with the glue joint itself breaking
Titebond II break point = 12.8 LBS - had a pretty consistent tear out of wood from the top veneer of the plywood.

Picture of the PL joint before breaking:
http://www.mikesprague.net/GlueTest/pho ... 43.44.html
Picture of the PL joint after breaking:
http://www.mikesprague.net/GlueTest/pho ... 48.41.html
Picture of the Titebond II joint after breaking:
http://www.mikesprague.net/GlueTest/pho ... 48.51.html

This is in no way a conclusive, scientific test and the data points are way too few but it gave me an idea for a particular joint I was have trouble with on a horn lens I was building.
The PL was very hard after 7 days and had some give to it before it broke. And, of course does not shrink at all. As highly suggested on this site - very good for box construction where wood joints might not fit completely tight or on blind joints where you can't validate the glue joint. I was surprised that it did not tear any of the wood like the Epoxy or Titebond II but the PL does not seem to soak into the wood. However, as everyone has pointed out, if the test joints were not completely flat and tight, the PL would have easily out performed - especially against the Titebond.

I plan on doing a more exhaustive test ...

[LelandCrooks]

Dampen the joint before glue up. In my test the pl ripped the ply apart.