Sticky business

We bond things together. It’s what woodshops do. Sometimes joinery or hardware helps, but the core of what we do is use adhesives to make natural and manmade products stick to themselves and to each other.

As the materials in those products continually grow more complex and diverse, choosing the correct adhesive can be a challenge. Woodshops are also getting more concerned about environmental issues and whether “safer” glues will do as good a job as the old reliable ones. The answers lie in educating ourselves as to available options and the best way to do that is to find a knowledgeable supplier.

Getting it right

Pierce Covert is the president of Glue Machinery Corp. in Baltimore (gluemachinery.com). For more than 50 years, the company has been supplying hot-melt and cold-glue machinery to woodworkers. He says the top four problems when working with adhesives are using too little glue and getting a poor bond; using too much, which slows the cure, causes squeeze-out and wastes money; not paying enough attention to temperature and humidity, both in the adhesive application and the storage environment; and using the wrong glue pattern.

“The glue pattern you select,” Covert says, “along with the pattern’s length, width, compression requirements, type of glue and even the age and maintenance level of your equipment all have an impact in determining just the right amount of adhesive to use.”

The best way to combat all of these problems is to work with your glue supplier to explore adhesive options that are best suited to your specific needs. And when choosing a vendor, Covert has some advice there, too: “How do you determine if a glue machinery supplier has what it takes to go beyond a one-time sale and actually become your long-term partner? Certainly, pricing will be an important factor in your decision. But there are other things you’ll also want to consider.

“Responsiveness is critical. If it’s hard to get a supplier to answer a call or return an email during the sales process, one has to imagine that it may be even more difficult to get his/her attention after the sale is complete. Some glue-machine companies only sell and service one or two specific lines of consumables and equipment. If your question is about a system that includes pieces of equipment from outside their lines, they aren’t willing to help. Others take a more vendor-agnostic approach. For the greatest level of service and flexibility, insist on a partner that can provide comprehensive service regardless of brand.”

In addition to adhesives, Glue Machinery Corp. carries a comprehensive line of cold application equipment including handguns, complete delivery systems, label gluers, roll coaters, pumps and pressure tanks, and pattern controllers and detectors. The company also supplies hot-melt machinery including handguns, benchtop hands-free systems, roll coaters and automatic bulk systems.

Daubond adhesives from Daubert Chemical Co. in Chicago (daubertchemical.com) are used for thermoforming, lamination and assembly applications. For shops needing to learn about the process, the company has a thermoforming training video link on its homepage. The segment begins with an explanation as to why Daubert offers a two-part adhesive, instead of the single component that many shops use. A one-part adhesive has a hardener already pre-mixed into the adhesive and the company says this causes the product to age quicker, which reduces its heat resistance. That allows vinyl on thermofoil components to move excessively, eventually causing the bond to fail. The two-part system also requires less heat during activation and during its useful life it has better heat resistance. The video explains the application process in detail, including recommending a HVLP delivery system. It covers mixing, calibration, prep, spraying, drying, press layout (including using temperature strips), quality control and cleanup.

Both Daubert and Glue Machinery Corp. point out the critical nature of temperature. If pre-heating is too low, the adhesive won’t activate and set properly and if it’s too high it can damage the vinyl.

Beyond thermofoil, temperature sensitive adhesives are also widely used in simple wood parts assembly. Hot-melt adhesive, such as item No. 3776LM from 3M (3m.com) can be a practical way to assemble drawers and other components in woodshops or hold things together until a mechanical solution takes over. According to 3M, the adhesive is 100 percent solids thermoplastic resin and engineered to remelt after bonding if exposed to high enough temperatures. Among the advantages of hot-melt adhesives are that it can be virtually invisible between surfaces, quickly fills gaps and reaches its bond strength within seconds. That last means that a woodshop can move assemblies right away, which eliminates the need for clamps, fixtures or additional drying time and energy.

Going green

As with every other aspect of the woodshop industry, working with adhesives has an environmental aspect. Most manufacturers cater to this need. For example, Henkel Corp. (na.henkel-adhesives.com) has construction and woodworking adhesives with reduced VOCs and formaldehyde-free formulations. Henkel has obtained GreenGuard certification for five of its trademarked brands: Dorus, Bondrite, Formica, Hybond and Permagrip.

On the front lines of environmental advances are research-and-development entities such as Sirrus (sirruschemistry.com). Its polymerization-on-demand technology currently provides fast cure speeds at ambient temperatures to significantly reduce cycle times, increase throughput and thereby reduce energy costs. In 2014, Sirrus signed a development agreement with Elmer’s Products for the development of consumer products from Sirrus’ Chemilian and Forza monomer platforms.

Another supplier worth watching for advances in this area is Sonoco Products (sonoco.com). The company makes Sonotube concrete forms and also produces liquid, dry-blend and hot-melt adhesives. Its SonoGrip brands are designed for assembly and wood applications.

Traditional solutions

Hide glue is still available as flakes that need to be dissolved in warm water or other solutions. According to Pennsylvania-based manufacturer L.D. Davis (lddavis.com), “it is sold in many different grams strengths allowing adhesive compounders the ability to adjust open time, tack level and viscosity for running on all types of equipment. The higher the gram strength, the stronger the glue. The stronger the glue, the less open time you have.” Animal products have been largely replaced by pharmaceutical industry byproducts nowadays as the source for hide glue gelatin.

Not all hide glue needs to be mixed. Titebond’s Liquid Hide Glue (titebond.com) from Franklin International is a ready-to-use product that “provides superior creep-resistance, offers excellent sandability and is unaffected by finishes. Its sensitivity to moisture allows for easy disassembly of parts, a critical benefit in antique restoration or the repair of musical instruments,” according to the company.

White glue, such as Elmer’s, is a PVA (polyvinyl acetate) compound and is very safe to use. The polyvinyl element is a plastic and the acetate is a salt that is formed when acetic acid combines with an alkaline or metal base. White glue is a viable choice for most standard casework and furniture, including dovetail and finger joints that need more open time. It has a slight disadvantage for repair shops in that no adhesive (including itself) will stick well to it once it cures.

Aliphatic resin emulsion or yellow glue such as the Titebond II brand is similar to and just as strong as white glue, with the added advantage that it has a shorter open and clamping time. The word aliphatic means that it’s non-aromatic or, more precisely, it’s a chemical compound of an organic class in which atoms are not linked together to form a ring. While white glue has a feature known as creep, which means it’s elastic enough to move slightly over time, yellow glue doesn’t slip as much, especially during glue-up. Water-resistant or waterproof yellow glue such as Titebond III is recommended for any wood project that will see occasional humidity (on a covered porch, perhaps, or in a basement).

Polyurethane adhesives such as Gorilla Glue are an excellent choice for outdoor furniture. They can require a small learning curve. For example, parts might need to be dampened and some brands will stain skin and foam up so clamping must be done right. Once the application process is understood and followed, polyurethane adhesive is an impressive solution.

Epoxy is a great gap filler and the waterproof characteristics of many brands allow it to be used on boats and items that are sometimes submersed. Many epoxies are formulated with very fast setup times, while others allow a little open time.

Instant Glue and other cyanoacrylate adhesives are ideal for small repairs like carving details that split with the grain by mistake. However, these products have a very short shelf life, especially after being opened, and there are some toxicity concerns. Read the labels.

This article originally appeared in the August 2017 issue.