when i strength tested these joints i got a lot of failures on the glue line and i'm
starting to wonder is my glue as good as i think it is so time for some glue tests
this is the glue i was using and i've got 10 other glues here to test against it and for all these i
made several samples where i glued one of these pieces onto this piece and these all came from
the same piece of 2x4 so they should be consistent and i'll be testing them with the screw jack which
is on top of some load cells to measure the force the test samples are clamped to this post and this
jack will push on here until it breaks first up construction adhesive that's john heist's favorite
so this shows the current force in kilograms and this kind of graphs it with just a character graph
and it's done broke at 58 kilograms next up arrow hot glue
so there's certainly some yielding happening here but it's still holding at 85 kilograms 86
87 this joint is yielding hot glue is a bit more flexible and it decided that
it yielded enough and just kind of decided back off of that hot glue is stronger than
construction adhesive who would have thought but i've got three more samples of each to go
i was very careful making my hot glue joints heating both surfaces hot enough that the glue
was liquid against both of them i just got to finish that break so i can get the next sample
i'm raising the jack to get the next two samples lepage carpenter's glue from a brand new bottle
i guess that one didn't beat the hot glue either this brand of epoxy from home hardware
this is the first one so far to really tear a chunk out of the wood
gorilla glue the kind that really foams up
well i think that was the strongest one so far
oh yeah broke some of the wood too weld bond
tight bond three
so i was definitely seeing some wood failure there
this uh this piece here split this one is using my big jug of le page which is
the same as this but i'm not sure if this has gotten too old or something
this was weaker than the glue from the new bottle but only by five kilograms and it's
only the first of four samples superglue from the dollar store
gorilla wood glue that's a pretty good showing and actually part of the wood failed here too
elmer's school glue
so the only one weaker than that so far was construction adhesive
five minute epoxy from the dollar store well that's the winner so far so that was
one of each so far the rest of these are repeats of the same kinds of glue
this sort of gradual yielding failure was very typical with a hot glue
though some hot glues performed much better than others
so
and here's my results bars in red are where the wood mostly failed
highest failure strength was the five-minute epoxy followed by weld bond super glue type on three
uh via bond epoxy that's a slow setting one old bottle of lepage the aerobrand hot glue
all only two samples a fresh lepage bottle gorilla glue gorilla wood glue school glue heavy duty hot
glue supposedly heavy duty construction adhesive was the second weakest and the weakest was some
random hot glue i had my glue gun so interestingly enough the fresh bottle of lepage carpenter's glue
was a little bit weaker on average than the old stuff so i think that's just random variations
and with quite a few wood failures here the ones in red are really mostly wood failures i really
need to retest the stronger glues with hardwoods the weaker glues construction adhesive the random
hot glue and the glue gun and the school glue all failed without tearing much of the wood
whereas a lot of the other ones you see here for instance this more wood failure than glue failures
or here but it's all quite random so i've remade all these with hardwood but i've eliminated the
weaker glues like construction adhesive and the crummy hot glue first hardwood test super glue
that's a lot more than i was getting before
oh oh oh i didn't clamp that hard enough super glue take two
once the force exceeds a certain level i slow down the stepper motor so it doesn't skip steps
and the wood broke well actually the glue joint failed but so did the wood weld bond
the slow epoxy gorilla wood glue
tight bond three
and here's my results with the maple the braking forces were substantially higher than i had with
the soft wood this is on the same scale even the glues where mostly the glue failed seem
to do better with the hardwood and this is using the same geometry as i had used for the softwood
and the softwood surface was actually pretty rough and fresh cut but perhaps the softwood just
doesn't stick as well to the glue as the maple does the percentage variability was also a lot
less uh if we go back to these scale to full graph you can see these jump around a lot more than what
i got with the maple so i trust these results more this is uh softwood and hardwood tests
and you can see all these a lot of these nearly doubled and the best one with the hardwoods was
a super glue followed by gorilla wood glue weld bond titebond three five-minute epoxy gorilla glue
lepage and aerobrand hot glue so which glue is best well it depends the super glue did best in
my tests but it's not suitable for large glue ups and just too much of a hassle to deal with
same with epoxy and the gorilla glue the type that foams up though it did okay it's just not suitable
for any sort of joinery where you might have a gap because it foams up and basically squeezes out
most of the glue which makes for a very weak joint of the woodworking glues with the maple gorilla
glue did best followed by weld bond followed by a tight bond this didn't do as well although with
a soft woods this was still the weakest one but not by much in terms of going bad i think
weld bond is the worst uh in fact the first bottle i bought from the hardware store had already
gone bad and i had to go back for another one titebond three goes bad not as fast and i think
gorilla glue goes bad a little bit slower than the titebond 3 but i'm not quite sure
and of course this doesn't go bad at all and it also may depend on what you're gluing
because even the glues that didn't tear a chunk out of the soft wood did better with the hardwood
than it did with a soft wood so i think that softwood was just maybe a little bit more oily
than the maple i was using and so the glue didn't stick to it as well as for construction adhesive
it's really not a woodworking glue but i may not have given this enough time to dry
i gave it 48 hours which might not have been enough but it is suitable for low temperatures
so are these glues but of course these are kind of a pain in the ass to deal with these ones
all have low temperature limits although this one seems to be the most tolerant based on the labels
not that i've tested all of these require at least 13 degrees or whatever that is in fahrenheit my
surprise here is that the gorilla wood glue out did the titebond 3 and this stuff is cheaper
and i think it goes bad slower so i kind of have to endorse it a little bit even though i really
hate uh this gorilla glue i only bought a tiny bottle because i knew the rest would go bad on me
and two more tests so this is construction adhesive on here but this time i wetted the joint
and then dried it for just one day on the radiator to see if this is going to glue better and then
this is gorilla wood glue and it's doesn't look the best anymore it's gone kind of chunky but i
glued these two joints with it to see if this gone bad glue still glues good construction adhesive
at 46 and 48 kilograms uh that's uh very weak uh perhaps the water didn't help any
because water is supposed to speed up how this cures or maybe the heat damage did i don't know
clumpy old gorilla wood glue oh the wood is split along here so that's not really fair anymore
so i've got splits all along this wood which allows it to
bend much better but the glue is still holding on
so this isn't really a glue failure second clumpy gorilla would glue
at 210 this is actually above average for my gorilla wood glue samples so uh that's really
impressive for uh gorilla wood glue that's gone all chunky on me so the lesson is if you can still
get into the bottle it'll still glue good i should also point to some tests done by wood by wright he
tested over 60 glues under different circumstances overall testing over a thousand wood samples
unfortunately his tests don't include a sort of a long range or long grain at a right angle test
because to me that's the most relevant because most wood joinery comes down to long going to
long grain at a right angle i've got his online google docs spreadsheet of all of his results
and he's had some overlaps with the tests that i've done so some of the glues that i tested he
tested as well and so i scaled his results because it's a completely different type of test he's done
and some of those kind of agree he also had surprisingly good results for super glue or
ca glue and these ones pretty close he didn't test hot glue not surprisingly
and unfortunately no gorilla wood glue because i was curious about that one so going forward
if i'm using hardwood and strength really matters i'll probably start using this more
but for most other things and for soft woods i'll probably continue to use this stuff because
it doesn't go bad it's cheap and it doesn't ruin my clothes if i get them on there the weld bond
did beat it by about 15 or so but i just don't like using that stuff very much so yes it is