Thoughts on Glues and Gluing.

March 16, 2023

Glues a sticky subject
I use a variety of glues in making my landing nets, and I would like to pass on my thoughts and understanding of this subject to you.
First I would like to talk about glues in general. I like to separate glues by their primary property.

A. Reactive or catalyzed glues. This group includes the epoxy resins and resorcinol glues (These glues typically are a two part glue with a resin and harder.) The glue may react with the natural lipophilic resins, phenols (natural alcohols) or saccharides (complex sugars) in the material glued to form their bond. In some cases such as the epoxies, they may rely mainly mechanical adhesion with the microscopic surface imperfections.

These glues are activated/catalyzed by a second additive. For urethane glues, such as Gorilla glue, applied or atmospheric moisture can act as the catalyst. For others glue, such as the polyester resins (sometimes called fiber-glass resins, think Bondo) a second chemical (MEK-P) accelerates the linkage between the polyester molecules. The urethane-formaldehyde powder glues contain the resin and hardner in the same tub. When water is added the reaction between the two components starts. (atmospheric moisture is enough to start this reaction and is the major cause of the limited shelf life.)

As a group, these are excellent at bonding dissimilar materials.

B. Affinity Glues. (the resin molecules have an affinity for each other and want to become entwined.) These glues work by the diluting fluid, such as water, either evaporating or being absorbed by the glued material. As the resin molecules of this type of glue come close each other they link up into a complex molecule that forms the glue bond.

For the polyvinyl acetate glues such as Titebond, the moisture causes the wood fibers to swell and are coated by the vinyl acetate resins, they a may also bind with a similar resins that are natural to wood.

Examples, that use a solvent other than water, are rubber cement, contact cement and P-47.

C. State change glues. Hot melt glue is the classic example with the glue melted in a glue gun. The glue quickly sets as it cools. This makes it excellent as stabilizer for an unusually shaped work piece or for quick assembly of a shop jig.

Another example is hot melt hide glue, the glue flakes are melted by heat in a glue pot. This glue quickly sets as it cools making quick clamping possible. This also means heat can be used to disassemble an object. This is seen as a benefit in the restoration of antique furniture.

Getting it to stick.

As I have broken the glues down into the various types some of their best applications become apparent.

The catalyzed glues generally have longer pot life and allow for more elaborate glue ups and clamping. They as a group tend to have greater water resistance. Their chemistry allows better adhesion of dissimilar materials.
The affinity glues, particularly those with water as a solvent are excellent for general woodworking and their interaction with the natural chemicals in the wood provide a strong bond.
The state change glues have limited use in building of a landing net. (There are some industrial hot melt glues that maybe the future of wood working, but probably won’t be a problem for me.)

How I use them

I use urethane-formaldehyde resin glue for most of my net building. It has a long pot life, excellent adhesion, is highly water resistant and machines well. (doesn’t gum up sanding belts) In addition it blends into the color of a urethane varnish or epoxy finish.

This glue does require mixing with water before use and can not be stored in a mixed state. It has a couple of disadvantages. Historically it was formulated with excess formaldehyde. This caused it to give off the excess formaldehyde when it was mixed and used. In the current formulation this is much better controlled. The current product meets national and California standards for release of formaldehyde. Good news, well sort of. It means that the chemistry of the product has changed. There is a recommended minimum pot time of 15 minutes. ?What? This means you should let the glue sit for 15 minutes before you use it, to allow for the glue to start catalyzing. The glue has a working time of 30 minutes ( time from application to final clamping) and a pot time of about 2 hours.

I have had students who report problems with adhesion. I have not had problems with this but I have some insight. The product you receive is really a two part product. The resin and catalyst are mixed in the same container, along with a wood dust filler. Typically this is sold in a plastic container. Plastic containers ARE NOT moisture proof. Most manufactures suggest a 1 year shelf life, when stored until normal conditions. Most of the glue I have bought over the years has been okay. When Dapp stopped making this product there was some post date product being sold on the internet. I am now buying this glue as Pro-glue. (Check Joe-woodworker.com or Vac-u-clamp.com ) (Woodcraft carries this glue but in 5 gallon buckets, go figure.) Cascamite is another brand available on Amazon. It comes in a 220 gram tub. Given that it takes about 3.5 oz or 100 grams to glue a net, it is a pricey product.

I have not had adhesion problems, EXCEPT once early in my experience. I glued up a very a beautiful curly maple net. The glue seemed a little crumbly in the plastic container, but I broke up the chunks and mixture it with water. So good so far. Glue up seemed okay and it dried into a nice powder as the net fell completely apart. (A similar event happened to a friend who let the net freeze in his shop before the glue had dried.) I now store the glue in GLASS jars to avoid atmospheric moisture activating the glue. AND would NOT use the powdered glue if it has any caking (dry lumps of glue powder).
This type of glue is still used extensively in the veneer plywood industry, where they use radio frequency to set this glue. (micro wave) As I have read the industrial literature about this glue one important point, that has not been pointed out in the general information, is that this glue is best “dried” / “set” in a 110-140 degree environment. One of my students tried this glue and let it set in his 50 degree shop. The whole event was a mess. I use a “hot box” (a shop made box with old fashion light bulbs for heat) to cure the glue. I have also used a small electric space heater in a bathroom for larger projects.

Two last insights about this glue. When you mix it, put the powder in a bowl (I use one hemisphere of cheap rubber ball and a silicon spatula) Put in a SMALL amount of water, mix that into a paste then keep mixing and adding water until you have the right consistency for the batch. Let it set for 15 minutes, (you may need to add more water before using).
I wear rubber gloves when gluing up a net, to protect my hands. When I need to clean up the glue from my hands, I use a mixture of white vinegar (1/3) and Joy dish washing detergent (2/3). (This glue is made by adding acid to urea, the acid in the vinegar and the ammonia in the detergent upset the chemistry of the glue and make clean up much easier.) (Dawn detergent doesn’t seem to work).

Why do I still bother with this glue. Long work time and pot time. Water clean up. Excellent machine-ability. Hidden glue lines. Excellent water resistance. I don’t have the slippery mess that I have with PVA resins. Also it doesn’t stick the inner tube tires together like epoxy or urethane (Gorilla) glue.

Do I use the other glues? you bet-cha.

The urethane glues for dissimilar materials or if I need a quick highly water resistant bond, Epoxy, as needed for its gap filling qualities, best with inlays and stabilizing metal parts. The PVA glues (Titbond) for about everything else.

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