The Sticky Issue of Adhesives, Glues and Tapes

Well, maybe I'm exaggerating just a little bit, but without modern adhesives, much of what we take for granted today would not stay together. Special glues hold our cars, our countertops, our furniture and our computers together. Adhesives allow thin things made of different materials to be bonded together in ways that are impossible with mechanical fasteners. Thin materials most of all demand creative fastening... and glues are often the best choice. The words "glue" and "adhesive" are oft used interchangeably. To set the technical record straight (even though I still reserve the "creative license" to call an adhesive a glue and vice versa), glue is defined as:
"... a hard, brittle gelatin made by boiling animal skins, bones, hoofs, etc. to a jelly: when heated in water, it forms a sticky viscous liquid used to stick things together" Webster's New Universal Unabridged Dictionary
Just makes you want to dance with the chickens, doesn't it? On the other hand, "adhesive" is any product, including glue, that can be used to bond two separate objects together. Unfortunately, no one adhesive works in all situations, though some may be used in all sorts of situations. Fun, right? The Natural Handyman carries a variety of different adhesives in his bag of tricks. Here is where you can take a peek inside... just keep these secrets between me and you. Happy gluing!!


Using Hot Melt Adhesive

I have grown fond of hot melt adhesive. Fast setting is its most noble attribute. However, it is not an especially strong adhesive and is intended to be applied somewhat thickly. This makes it generally unsuitable for quality finish woodworking. I have seen inexpensive cabinets literally fall apart because they were assembled with hot melt.
But this is not to take away from its versatility and usability. It is employed extensively in craft making, artificial flower arranging, in manufacturing to seal cardboard boxes and in some product assembly. Hot melt glues are available in high and low temperature formulations.
It is great when used as a secondary adhesive, to hold items together for screwing or primary gluing (see the Famous Glue Trick).
There are many types of hot melt adhesives manufactured for professional and industrial use that far exceed the strength and durability of the typical hardware/craft store products. The seaming tape that carpet installers use is glued with a special hot melt adhesive and, as I'm sure you know, carpet seams are about as permanent as anything in this life!
Adhesive Technologies, SDA/Craft Technologies, H.B. Fuller and 3M are all major manufacturers of hot melt glues, and their products are widely available in hardware, home and craft stores.
Tips and tricks...
Hot glue guns are simple to use. Plug the gun in, allow it time to heat up, and then squeeze the trigger to apply the adhesive. Melted glue very hot and will burn the skin instantly, so be careful! Press the parts to be glued together and hold till set.
Sometimes the glue stick will not feed properly and may need a push. Feeding too much glue at once will cause the gun's mechanism to slip against the stick till more of the glue stick melts. Also, once a stick is almost used up the gun may need a second stick to push the first through.
Different hot melt glues have different setting times, and this will determine its proper uses. Some glues dry almost instantly and are best for situations where repositioning of the parts is unlikely and speed is important, such as in many craft projects. On the other hand, slower hardening glues are better when it may take a little time to position the parts, such as when installing cleats for drywall repairs. In my own work, the only hot melt adhesive I used was a slow-setting type. I realized that each time I changed the glue, I had to waste whatever was remaining of the stick I started. Waste not, want not!
Most importantly, hot melt glue is designed to be applied thickly and seems to stick best when it is not squeezed too thin. That means it can't be used where the tolerances are tight, such as in fine woodworking. No problem, since there are stronger, better glues designed for woodworking, such as polyurethane glue or good old wood glue, that allow the repositioning time needed to apply clamps.

Duct Tape... Uses and Abuses

I was, at one point in my career, a duct tape addict. I would lash together lumber, repair hammers, fix my trusty wooden tool box... ad infinitum. Then, in my travels through thousands of homes, I came to see the weakness in duct tape as some repairs done with it days, weeks or months before began to fail. The weakness in duct tape's armor is due to three factors... poor adhesive quality, heat and ultraviolet light.
The adhesive used on duct tape is tenacious. If you've ever torn off a piece and had it touch itself, you know the meaning of sticky! Straight to the garbage can for that strip, yessirree. But as strong as this adhesive is, it is not really permanent like a setting-type adhesive. And some "bargain basement" duct tapes are not worthy enough to wrap fish!
Heat can soften duct tape adhesive, making it lose strength. If there is weight or stress on the repair, this softening can cause the tape to slip and the joint or attachment to fail. This can be prevented by use of a secondary fastener such as a clamp or strap. A classic example of this faux pas happened to a customer of mine a number of years ago...
A repair person was called in to troubleshoot and repair a dryer vent line which no longer blew to the outside. All visible connections seemed to be OK, so he had to cut the wall open behind the dryer to assess the situation. What he found was a failed junction between two pieces of plastic duct hose connected together at eye level by a 12" long piece of 4" round aluminum ducting with duct tape alone as the fastener!
I suppose he thought that the last guy just didn't use enough tape, so he wrapped the connection in what appeared to be half a roll of duct tape... with no other fasteners... and closed the wall back up. It took about six months for the repair to fail. I'm amazed it lasted that long! The heat from the clothes dryer caused the connections to separate as the tape softened, until the two sections of pipe totally separated from each other within the newly repaired and painted wall. Darn..
The repair guy, of course, has never been heard from again.
I don't have the trust in duct tape I once had. So as a rule, unless I am looking for a temporary repair, I always find a way to supplement the strength and air-sealing properties of duct tape with a more permanent fastener!
Using duct tape outside...
No, I didn't forget about the effect of ultraviolet light on duct tape, Randy. If you don't know Randy, he is the editor of the Feather River Canyon News, and a while back he reminded me of the problems in using duct tape outside for anything but temporary repairs... especially when exposed to the sun. He likened it to a "a powder-coated set of threads with dried up adhesive." Enough said!
However, I understand that there are some newer duct tapes that are UV-resistant, making them more suitable for outdoor use. For example, both Gorilla Tape and Scotch® All-Weather Tape are outdoor-friendly. Be sure to read the label before purchasing and duct tape for outdoor use.

The Many Types of Wood Glue

Good question! You would think that with the chemical marvels described above a water-based wood glue would have gone the way of the dinosaur. You couldn't be more wrong. In its own element... that favorite of termites cellulosis dinnerosis (a.k.a. wood)... good ol' wood glue... is as strong or stronger than those other fancy-schmancy adhesives.
Why? A number of reasons...
Wood glue is designed to set thin so there are no gaps between wooden parts.
They set slowly or quickly, depending on the glue chosen and your needs.
They are available in interior, water resistant or waterproof varieties.
There are three basic types of wood glues to be concerned with. There are of course variations on these and new glue products and formulations are popping up like mushrooms. So experiment if you like, but these three are recognized as the premier woodworking glues.

PVA (polyvinyl acetate)
PVA's are the traditional wood glues, and some of the most common adhesives. They are also called "aliphatic resins". They provide a strong wood-to-wood bond but will not adhere strongly or consistently to nonporous materials, such as metal or plastics. It is important to use clamps to hold the wood parts firmly while the glue is drying. Any movement after the initial "set", usually occurring in a few minutes, will cause breaks in the glue bond that will make it much weaker.
PVA's do not stick well to other glues, so they are of little value in furniture repair where old glue failure is the culprit... loose chair spindles immediately come to mind. Though the "pros" tell you to remove the old glue to give the new glue a chance to absorb into the wood, in reality it is often difficult or impossible to remove the old glue sufficiently to make a lasting repair unless the entire piece is disassembled. Instead, use a solvent-based adhesive, such as GOOP (see article on GOOP for more info).
Though widely used by woodworkers, PVA's are not really suitable as a primary adhesive or for edge gluing... attaching boards together to make wide surfaces such as tabletops or other furniture. They are "plastic", so without other supporting fasteners such as screws or nails, metal reinforcements or dowels, the glued joints will eventually break apart. For pro-quality wood gluing where extra fasteners might get in the way, read the sections in this chapter on polyurethane glue and hide glues.
One of the more well known PVA adhesives... for all parents and anyone who was ever a kid... is Elmer's White Glue... effective on paper but not very strong on wood. Yellow wood glues offer more strength and greater water resistance. Note that PVA glues are not completely waterproof, however.
Some examples of PVA glues are Titebond Original Wood Glue and Elmer's Carpenter's Wood Glue.
Water-resistant PVA glues have all the benefits of regular PVA glue but have increased tolerance to moisture and extra mildew resistance. Because of these additional benefits, I use them for all applications PVA glues are suitable for rather than keeping both standard and water-resistant PVA in my larder.
Titebond II and Elmer's Carpenter's Exterior Wood Glue are two widely available brands of water-resistant exterior glues.

Polyurethane glue
Polyurethane glue is one of the best waterproof glues available, but until recently was not available outside professional circles. It is a one-part adhesive that will adhere to wood, metals, stone, ceramics and many plastics.
Polyurethane glue does not dry like PVA glues, but instead chemically reacts with moisture in the objects being glued or even in the air. This reaction causes an expansion of the glue, filling all voids and giving an exceptionally solid glue joint. If the material is dry, spraying a light mist onto it before gluing accelerates the curing process.
In many ways, polyurethane may be the best wood glue. It both accepts wood stains and sands well in thin coatings, neither of which are true for PVA wood glues. Most other adhesives act as a sealer on the wood surface. And removing these other adhesives can be difficult because they dry to a "gummy" texture that resists removal from the wood by sanding... the second strong reason to consider trying polyurethane glue for your next project.
Polyurethane glue has a longer setting time than PVA glues, so you have more time to adjust misaligned clamps and other errors before you reach the gluing world's version of the "point of no return".