Glues and Adhesives Oxford MS
Glues and Adhesives
When I was growing up, the only glues I used were model glue and various brands of white paper glue. Even the local hardware store only stocked two or three types of adhesives. Now when you walk through your hardware store you are faced with a daunting array of glues and adhesives for every possible application. The problem, as with any large menu, is how do you know which is the right one?
Unfortunately, there is no such thing as a miracle adhesive that will work with all types of materials. As with many other homeowner decisions, you need to understand the basics.
All glues are carefully formulated products with specific properties, and they perform well only if the conditions, such as temperature and humidity, are favorable. Gluing well is a matter of knowing how to get the best performance from the glues you use, while also knowing their limitations. More importantly, you need to understand the relationship of the glue to the type of materials you are trying to bond. "Ultimately, understanding what product to use and how best to approach a particular project are critical elements in achieving success,
according to Craig Stone of Franklin International (Titebond). "Evolving product technologies, diverse applications, new substrates and materials and environmental impact are all important criteria that should be considered.
Glues vs. Adhesives
Glues are based on polymers, such as starch and protein, that are derived from natural sources, such as rice flour or cattle hides. Natural glues include rice and wheat pastes, fish glue, hide glue and casein glue. They consist of natural ingredients that cure by moisture loss, heat loss or a combination of both. These glues are reversible, meaning they can be reactivated with water after they harden.
The earliest glues were hide glues, and these are still in use today. Hide glue is made from animal products and is extremely useful for projects like musical instruments that often require disassembly to make repairs. Because heat and humidity cause hide glue to release its bond, its a relatively simple matter to separate pieces without damaging them. Hide glue also cures slowly, so it can be a good option for difficult furniture joints or constructions that take a long time to assemble.
Adhesives, on the other hand, are based on polymers that are chemically synthesized, like polyvinyl acetate (PVA) resins found in white and yellow glues. Other adhesives include epoxies and polyurethane glue. Synthetic glues are either nonreactive or reactive.
Nonreactive glues, such as ethylene vinyl acetate (EVA), PVA, contact cement and hot-melt glue, are formulated from synthetic ingredients but cure like natural glues by releasing water, solvent or heat.
Reactive glues, such as urea resin, resorcinol, epoxy, polyurethane and cyanoacrylate (CA), are formulated from synthetic components and cure primarily by chemical reaction. Most people use the terms glue and adhesive interchangeably, as we will for this article.
Properties of Glue
Glues can be either water based or nonwater based. Water-based adhesives are easy to handle, but they can add moisture to glued work, which in some cases would be undesirable. For instance, if youre laminating an unstable wood like beech or sycamore, youre better off using an adhesive that contains less water. Most natural and nonreactive synthetic glues (except solvent-based contact cement and hot melt) are high in moisture content. Reactive synthetic glues, with the exception of a few resorcinols and ureas, generally dont contain a significant amount of moisture.
Glues also vary in toxicity. The glues that offer higher levels of performance and power are often more hazardous than those that are not as powerful. This is especially true when comparing different variations of the same kind of glue. For example, high-fume urea resin glue (which emits powerful formaldehyde vapors) usually outperforms low-fume urea resin glue, which is safer and less noxious.
Environmental regulations are a major factor in the development of new adhesives. Concerns about toxicity and residual pollution push the industry to develop alternatives. Technological advances also spur new development. Dave Pinsonnault, development manager for the R&D team at Loctite notes that, "The latest trends in adhesives are high-performance, latex-based adhesives that meet and exceed the performance of conventional solvent-based adhesives and innovative, user-friendly delivery systems for construction adhesives and sealants. Examples of these include new Loctite Power Grab construction adhesive, a latex-based adhesive that has no odor or VOCs (volatile organic compounds) and offers superior bonding strength. This is also available in a pressure pack pressurized container that gives users more control and eliminates the need for a caulk gun.
The variety of glues and adhesives has increased significantly over the past 40 years. There is an adhesive for every application. You just need to make sure that you understand the advantages and disadvantages of each. Take some time to read the labels. Also visit the websites of the different manufacturers to get a detailed explanation of each product. Pay attention to new products and look for those with the least risk. All it takes is a little bit of effort to ensure that your project gets put together properly and lasts a lifetime.
For general construction applications, your best bet is construction adhesive. Sold in different sizes of tubes for use in caulking guns, or as squeeze tubes, construction adhesive is a thick, sticky bead that fills gaps and adheres well to a variety of surfaces. It is waterproof and can be used on wood, masonry, drywall, ceramic tile and many other materials. Most construction adhesives are made from polyurethane (although, as with other adhesives, there are many different varieties). They are good for general-purpose gluing for house repairs and any project that needs a lot of strength and water resistance. They are also good for exterior wood projects, although they can be expensive. Some types of construction adhesive, however, wont work well on pressure-treated lumber, so check the label carefully for the appropriate uses. Unfortunately, they can be messy to apply and often leave a visible residue.
Epoxy is another all-purpose alternative and is the only type that is generally stronger than the material it bonds. It resists almost anything from water to solvents. Epoxy can be used to fill cavities that would otherwise be difficult to bond. It is waterproof and bonds most materials, porous or not, except PVC or Perspex. Use it in warm temperatures, but read the manufacturers instructions carefully, since curing times vary, and the mixture of resin and hardener must be precise.
Epoxy is the best product for anchoring bolts and other materials to masonry -- including concrete, stone, brick and other similar materials. Epoxies come in a two-part formula of catalyst and resin, and are usually mixed together in equal portions to form an adhesive. There is a variety of epoxies, all of which are very strong and durable. Most have a very long shelf life, provided the components are kept separate. Once they are mixed, an irreversible chemical reaction begins, and you have a limited time to use them.
Epoxies take three basic forms: liquid, putty and paste. Liquid epoxies are easiest to use when you have a hole to fill, such as cementing a bolt into a hole in a concrete floor. The two components are mixed in a cup or other container, then poured into place. Simpson Strong-Tie, a leading manufacturer of joist anchors and other construction fastening products, offers an easy-to-use epoxy syringe. It consists of two tubes of liquid with a twin plunger handle; press down on the handle, and the two liquids flow out of the tubes and into a common nozzle, where they are mixed and dispensed.
Another type of liquid epoxy comes in a glass tube and is designed for anchoring bolts, rebar and other similar applications. You simply drill a hole, insert the tube in the hole, then hammer in the bolt, which in turn breaks the tube and allows the two components to mix and harden.
Putty- and paste-type epoxies come as two separate sticks. Simply cut an equal length off each stick, knead them together in your hands or on a suitable surface, and then place them in position. The putty works well for vertical and overhead applications, and it is easy to measure and mix only as much as you need.
One of the most popular glues around the house is CA adhesive, best known by the brand name Super Glue. CA adhesives dry almost instantly -- as anyone whos stuck their fingers together can attest -- and work well on a wide variety of surfaces. (By the way, if you happen to find yourself in a super-sticky situation, a little bit of acetone nail-polish remover helps to unglue fingers.) The only trigger that CA adhesives require is the hydroxyl ions in water.
An interesting application for CA adhesive is their use to close wounds in place of stitches (although you should definitely not try this yourself). Researchers found that by changing the type of alcohol in CAs -- from ethyl or methyl alcohol to butyl or octyl -- the compound becomes less toxic to tissue.
Another favorite is contact cement, which is applied to both surfaces being joined and allowed to dry. The two glued surfaces are then brought into contact with each other, and the bond is instant and very strong. This makes it an excellent adhesive for gluing together materials that are nonporous, such as plastic laminate countertops in kitchens and bathrooms, where you have two very wide pieces of material and both have limited porosity, such as particle board (the standard countertop substrate) and plastic laminate. Unfortunately, contact cement is somewhat sticky and messy to apply. Also, there is no room for error with contact adhesive -- once the two glued-up pieces contact each other, they are stuck for good!
Contact adhesive is available in a traditional solvent-based formula or a newer water-based formula. Solvent-based contact adhesive dries in less than 15 minutes but releases a highly flammable solvent into the air. Users must take precautions to assure adequate ventilation to prevent accidental ignition of the fumes. Read the label for all warnings.
Hot-melt adhesive or thermoplastic adhesive is another variation that bonds almost anything, including many plastics. It generally comes as a stick that is inserted into an electric glue gun. Apply it, press the work together and hold for 30 seconds. No clamping is needed, and it cleans up with thinners. It hardens within seconds, is very easy to use and works great for all types of craft projects, from fabric to paper. The gun tip gets really hot, which can cause burns, and it also has a very short working time. It isnt very strong, so its not a good choice for woodworking projects. Hot-melt glues, such as Titebond HiPurformer, use polyurethane to form an extremely strong waterproof bond with fast set times for most materials.
Working With Wood
Where are many options for gluing wood to wood. The most common is aliphatic-resin (AR) adhesive, or yellow woodworkers glue. Two of the most widely recognized brands are Elmers Glue-All and Franklin Titebond. Generally AR adhesives are for interior use only. They are easy to use, require no mixing, are nontoxic and clean up with water. They also sand cleanly without clogging the sandpaper and leave an invisible glue line if the joint is tight. Yellow glue sets up quickly and only takes about an hour to dry. It is designed to bond bare wood, since painting or staining the wood blocks the pores, thus keeping the glue from penetrating into the wood. It has a shelf life of about two years, provided it is tightly capped and protected from freezing.
Yellow glue is generally not recommended for gluing wood veneers, since it never fully hardens and may allow veneer to "creep,
or move, during seasonal changes in humidity. Yellow glue also has a tendency to bleed through and discolor the veneer. It is also a poor choice for things like high-end exterior doors or outdoor furniture. For these purposes, there are water-resistant formulations, such as Franklin Titebond II and Elmers Weather-Tite. These are technically known as cross-linking PVAs, and they cure through chemical reaction, instead of evaporation. For general woodworking use, this glue is interchangeable with normal yellow glue except that it cant be cleaned up with water after it cures. These glues are weatherproof and safe for most outdoor uses. Elmers Weather-Tite is a thicker gel formula that reduces running and dripping.
White glue can also be used for wood. Its inexpensive and can be used for lightweight gluing, like craft projects. It is nontoxic and can be stored for a very long time. However, it has poor water resistance, isnt very strong and is hard to sand. Both glues can be used on paper, cloth and a variety of other porous surfaces.
Polyurethane adhesives, such as Titebond, Excel and Gorilla Glue, are newer, premixed liquid adhesives that are fine for exterior or interior use. Once applied to the wood, they have a longer setup time than AR glue, as much as 15 to 20 minutes, which gives more time for positioning the glued pieces correctly. Polyurethane adhesives react with the moisture in the wood and the air to begin a catalyst process somewhat similar to epoxy. As the glue dries, it begins to foam slightly, and the dried foam scrapes or sands off exposed surfaces very easily. The only drawback is that polyurethane glues have a shelf life of only about a year.
Barry Chalofsky is an environmental land planner and author of The Home and Land Buyers Guide to the Environment. Visit his website at http://www.erols.com/profed.