Comparing Adhesives

Pros discuss the relative merits of various glues in cabinetmaking and woodworking applications. October 20, 2005

I'm looking for a better glue system, other than Titebond. Id like something that is easy to use, not too expensive, with long enough open time to glue up casework, but is fast setting. Does PUR glue need clamping? Is the open time long enough to clamp if you need to?

Forum Responses
(Adhesives Forum)
From Jeff Pitcher, forum technical advisor:
There are actually two different PURs available for use in most shops. One is a liquid PUR such as Gorilla Glue or Excel. The other is a PUR Hot Melt available from a number of companies.

Generally, Titebond is preferable to liquid PUR unless you need something waterproof or you are gluing things other than wood. For most applications Titebond is more than adequate and significantly less expensive than liquid PUR. Both must be clamped, both have about the same open time but Liquid PUR is 3-4 times the price and doesn't clean up well.

Hot melt PUR might be a good alternative if you can justify it in terms of increased production and decreased labor cost. If you can't see real savings in these areas you'll be spending five times the money on adhesive with no real increase in bond quality.

From contributor B:
About fifteen years ago, when PL Premium polyurethane construction adhesive was introduced, I discovered that PL pretty much welds to melamine as well as any other porous joint, such as plywood edges to solid wood, covering most case joinery.
I embarked on a test. I made a bunch of 4" x 4" x 4" L-shaped sample joints in melamine and birch ply, to test in an arbor press with a weight scale to record the threshold weight the joint would hold at the point of breaking.

Joints were dado, biscuits, and screws using Titebond, versus a set of joints that were simple butt joints glued with PL premium, and a set of butt joints with PL and a 3/4" x 3/4" cleat glued and pinned on (no clamps) for added glue surface area.

The results were as follows:
Melamine: The screw joints broke at around 30 lbs, same with the biscuits. The dados went to 37 lbs. Dados are far weaker than people think due to the fact that the cutting of the groove destroys the integrity of panel.

PL broke at around 45 lbs, ripping out the HDPB core, but no joint failure.

Heres the real discovery:
The joint with the PL and glue cleat broke at 127 lbs!

Essentially the same results with the pressure tests on the plywood.

My whole cabinet business was revolutionized, and all my case joinery utilizes PL premium butt joints and two "locator" nails to keep the joint from slipping during cure. I put a couple deep-throat clamps in the middle to aid in pressure till set. Its hard to measure, but I figure I saved about 10 - 15% overall time by eliminating the time consuming joint cutting operations like insertion dowel, dado, etc.
For face frames I use PL all the way. I would use Titebond only for solid wood-to-solid wood.

From contributor C:
We recently had a Jet-Weld gun in our shop for a week or so. It is a PUR hot melt system. I was interested in using it to bond mitered moldings, including crown moldings. After some testing we found we could get a perfect crown molding joint bonded with a 90 degree corner. We made a simple fixture that gave us a 90 degree corner to work from. We then glued one surface, rubbed the two corners together to spread the glue and held in position for 15 second. In five minutes you could sand and you could handle the parts in 20 minutes. It was very strong. The down side was that the tube could only stand being heated for 16 hours before it would have to be discarded, and it was expensive. For our purposes we did not have the need for the added speed. I could see the value in the future to increase flow and reduce labor. If I was installing in the field I would get a Jet-Weld gun or one of the smaller Franklin systems. The speed and strength is amazing and you could eliminate many, if not all pins. You would add about $20 an install in material.
I got the local 3M rep to loan us the gun.

From contributor D:
For tricky casework PL Premium is the only way to go. It actually lubricates tight joints so they fit well without grabbing. I'm starting to use it for tabletop edge-to-edge laminations simply because it can be sanded and the glue line looks and stains like wood. Fewer clamps are needed too.

From the original questioner:
I'd like to try the PL but where do I get some PL Premium to try? Is it the same "PL" line of adhesives I see at Home Depot? With the short shelf life of PUR glue, I don't think it would work here.

From contributor D:
All the big hardware stores carry it. I buy the big tubes.