Wood glue
Wood glue is an adhesive used to tightly bond pieces of wood together. Many substances have been used as glues.[1][2][3]
Types of wood glue
- For many centuries animal glue, especially hide glue was the traditional glue for all kinds of woodwork. It is still used today, mainly for musical instruments (lutherie) and in making sympathetic repairs to antique furniture. You can now find a liquid version of it, Old Brown Glue. Hide glue does not creep. Hide glue joints are easy to repair, by just heating and adding more hide glue.
- Urea-formaldehyde resin adhesives feature low cost, low cure temperatures, resistance to microorganisms and abrasion, and light color. It does not creep, and can be repaired with epoxy. Can rapidly deteriorate in hot, moist environments, releasing formaldehyde (a carcinogen);[4][5][6][7]
- Resorcinol-formaldehyde resin glue is very strong and durable (resisting immersion in boiling water, mild acids, salt water, solvents, mold, fungus, ultraviolet light, etc.). It must be mixed before use (liquid resin and powdered catalyst). It has a dark purple color which may be objectionable in some uses. Toxic.[8] For many years, the FAA has stated that "Resorcinol is the only known adhesive recommended and approved for use in wooden aircraft structure and fully meets necessary strength and durability requirements"[4] for certificated aircraft, however in fact the vast majority of wooden aircraft built in recent decades (mostly amateur-built aircraft) instead use other types of adhesives (primarily epoxy resin systems) which offer greater strength and even more importantly, much less criticality in perfect application technique. Most newer adhesives are much more tolerant to typical construction mistakes (such as small gaps or misalignments between parts) than resourcinol, which offers virtually no tolerance for such everyday construction situations. This can pose major difficulties, especially in complex assemblies. However, resourcinol is still used by some builders/restorers, and is commonly seen in vintage aircraft.;
- Phenol formaldehyde resin is commonly used for making plywood. It is cured at elevated temperature and pressure.;[4]
- Casein glue was used to make strong and robust joints in early aviation, but fell out of favor due to its susceptibility to attack by bacteria.
- Hobbyists commonly use polyvinyl acetate (PVA), also known as "white glue" or "hobby and craft", and aliphatic resin emulsion, commonly referred to as "carpenter's glue" or "Yellow glue", which has similar relative ultimate strength. The two have different grip characteristics before initial set, with PVAs exhibiting more slip during assembly and yellow glue having more initial grip. PVAs are non-toxic and very easy to use, but hard to repair since nothing else sticks well to the hardened glue.[7] PVAs will creep under constant load.
- Polyurethane glue (trade names include Gorilla Glue and Excel) is becoming increasingly popular, especially where water resistance is required. They bond to textile fibers, metals, plastics, glass, sand, ceramics, and rubber, in addition to wood. However, in water-saturating tests, polyurethane bonds "were much less durable than the resorcinol bonds on both [Douglas-fir and yellow birch]."[9]
- Epoxy, usually as a two part mix system, cures under a wider range of temperatures and moisture content than other glues, does not require pressure while curing - clamping actually weakens bond, and has good gap-filling properties - near perfect joints with very small gaps actually produce weaker bond. Bonds to most cured wood glues (except PVA).[7][10] Two part epoxy adhesive is very resistant to ultraviolet light and salt water, most epoxy is heat resistant up to 350 °F, the formulations containing powdered metal and rubber or plasticizers are very tough and shock resistant. Epoxy can trigger long-term sensitivity (allergies) from overexposure, and is often expensive.;[11]
- Cyanoacrylate (Crazy glue, Superglue, CA or CyA) is used mainly for small repairs, especially by woodturners. Bonds instantly, including to skin. Cured CA is essentially a plastic material. Versions are available that are able to wick into tight joints but bond with reduced strength because much drips out and much soaks into the wood leaving very little on surface for the bond), or thicker formulations (gel) which can fill very small gaps, do not flow out of the joint, and do not soak so quickly into wood. Thinner cyanoacrylate glue does not bond more quickly nor form shorter polymer chains than the gel version when used on wood. The chemical nature of wood significantly delays polymerization of cyanoacrylate. When it finally polymerizes in a wood joint, enough gel remains for a better bond than with the thin version. Too much glue is a weakening factor but almost no glue at all remaining in a wood joint attempted with thin super glue leads to weak or no bond at all.
Versions are also available that are foam safe (regular CA dissolves most plastic foams) which are usually also marketed as low odor. Cyanoacrylate is stiff but has a low shear strength (brittle) thus normal wood bending can break the bond in some applications. Often, too much adhesive is applied which leads to a much weaker bond. CA has quickly become the dominant adhesive used by for builders of balsa wood models, where its strength far exceeds the base materials.;
Usage
Several wood glues have poor "gap-filling" ability (they bond tightly to wood, but not to itself). Therefore, woodworkers commonly use tight-fitting joints that need surprisingly little glue to hold large pieces of wood. Most wood glues need to be clamped while the glue sets.[2] Epoxy resins and some other glues can be thickened with structural fillers (or with thicker formulations of the resin) to help fill gaps, however it's obviously preferable to try to minimize gaps in the first place.
See also
External links
References
- ^ Patrick Spielman (1986). Gluing and Clamping: A Woodworker’s Handbook. Sterling Publishing. ISBN 0-8069-6274-7
- ^ a b http://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr113/ch09.pdf Forest Products Laboratory Wood Handbook, ch. 9, Adhesive Bonding of Wood Materials, Charles B. Vick, retrieved 2009-10-31
- ^ http://www.lowes.com/lowes/lkn?action=howTo&p=BuyGuide/GlueGuide.html Lowe's Guide to Glues and Adhesives, retrieved 2009-10-31
- ^ a b c http://rgl.faa.gov/REGULATORY_AND_GUIDANCE_LIBRARY/RGADVISORYCIRCULAR.NSF/0/99C827DB9BAAC81B86256B4500596C4E?OpenDocument FAA Advisory Circular AC 43.13-1B CHG 1, Acceptable Methods, Techniques, and Practices - Aircraft Inspection and Repair, retrieved 2009-11-01
- ^ http://www.fpl.fs.fed.us/documnts/pdf1996/conne96a.pdf Anthony H. Connor, "Urea-Formaldehyde Adhesive Resins", Forest Products Laboratory, USDA Forest Service, retrieved 2009-11-01
- ^ http://www.djmarks.com/stories/djm/Woodworker_West_Article_On_Urea_Formaldehyde_Glue_109015.asp David J. Marks, "Working with Urea Formaldehyde Glues", Woodworker West, September/October 2007, retrieved 2009-11-01
- ^ a b c http://www.sawmillcreek.org/showthread.php?t=21822 Bob Smalser, "Are Your Glue Joints Repairable?", retrieved 2009-11-09
- ^ http://www.dap.com/docs/tech/00030205.pdf DAP Technical Bulletin, DAP Weldwood Waterprof Resorcinol Glue, retrieved 2009-10-31
- ^ http://www.treesearch.fs.fed.us/pubs/5964 "Strength and Durability of One-Part Polyurethane Adhesive Bonds to Wood", Charles B. Vick, E. Arnold Okkonen, Forest Products Journal, vol. 83, No. 11/12, retrieved 2009-11-01
- ^ http://www.gurit.com/core/core_picker/download.asp?documenttable=libraryfiles&id=1109 "Bonding with Epoxy in Wood Construction", Gurit, retrieved 2009-11-03
- ^ http://www.cpadhesives.com/media/ClassicBoatAppendix.pdf Larry Pardey, "Superior Adhesives for the Millennium", retrieved 2009-11-08