Glues

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Glues keep everything together.

    Trees make lousy furniture.  The bark flakes and scratches, the wood cracks, and the roots embedded in the ground make it rather difficult to "pull up a chair."  So we cut the tree down, strip off the bark, saw the wood into boards and dry it (thereby making it much lighter), then go about reassembling the tree into something better suited to our needs.  The key ingredient to rearranging the wood to fit our design is joinery, and most wood joints commonly used today rely ultimately on glue to hold the wood together.  Glue goes back at least 3,000 years (that we know of), and the earliest glues were based on animal-derived proteins, known today as hide glue, and still in everyday use.

    The modern woodworker has a full array of glues to fit every need (except fixing lousy joinery), and most project timetables.  Choosing the right glue for the job can make the difference betwen a joint failing in the shop, or in use, or fifty to a hundred years from now.  The right glue cannot, however, make up for poorly cut joints, fill gaps with a bond as strong and flexible as the wood, or accept stain if it gets on the exposed face of the wood.  (So, clearly, there's some room for  technological improvement; right?)  Until then, make sure your joints are tight, and take care to remove all glue squeeze-out before staining. (Tip: look for the shiny spots, that's glue -- and wipe down with mineral spirits  before staining to highlight any errant glue spots.)

Safety First!
Safety in the workshop is YOUR RESPONSIBILITY alone; I make no warranty as to the safety of any technique or tool shown or described on this site.  Before beginning any project, you must understand woodshop safety, know how to safely operate any machinery that is to be used in the project, and understand the safe use and any potential safety hazards involved in the use of all materials to be used in the project.  See the General Safety Notice and the Chemical Safety Note for additional information.

G L U E   S E L E C T I O N   C H A R T 

Glues Commonly Used in Furniture and Cabinetry

Bond Strength

Bond strength on hardwoods.  Very high means even a very strong wood will break before the glue bond does (in a properly formed side grain joint).

Water Resistance

Very high is suitable for use below waterline, medium is suitable for often damp locations such as shower rooms, when the wood is properly protected by a polyurethane finish.

Working Time

Working time refers to the approximate time  (in minutes) between assembling glued surfaces and applying clamping pressure.  It is the amount of time you have to make adjustments to the assembly.  Open time is the time between spreading the glue and assembly, and clamping time is the time the assembly needs to be clamped before it reaches full bond strength.  Read the product label for specific information about these various times.

* Contact cement sets up for use in about 10-30 minutes, but bonds instantly when the two treated parts make contact.  Thus, its actual working time would technically be zero.

Multi Material

The ability of the glue to produce a full-strength bond on various dissimilar materials, such as wood, metal, most plastics, ceramics, and rubber.  For best results, the mechanical properties of the glue (flexibility, strength) should be matched to the properties of the materials being bonded.  Cyanoacrylate, for example, does not usually bond well to flexible, rubbery materials.

Flexibility

Relative flexibility or resilience of the glue line.  Flexible glues tend to withstand shock loads and bond rubbery materials better, and may make for more a more tenacious grip when wood warps as the result of exposure to moisture.

Resistance to Creep

Hard or tough glues usually work better for bent laminations, as they do not let the two sides of the joint slip over time, thus preventing the bent curve from straightening out.

Removable

Some glues can be un-done easily by heat, moisture, or solvents.  Others cannot, which makes repairs difficult or impossible.

Chemical Resistance

Resistance to acids, alkalines, solvents, etc.

G L U E   T Y P E S   &   P R O P E R T I E S 

Note: the following selection of glues is limited to those that are commonly used for bonding wood in household or light industrial settings.

Aliphatic Resin (Yellow Carpenter's Glue, e.g. Franklin Titebond™)

Non-toxic, non-flammable, type I is not water resistant, type II is water resistant, type III is waterproof; solvent & heat resistant, sets in 45 min, fully cured in 24-72 hrs.  Strong to very strong, dries hard & translucent, can be colored with water soluble dyes, sandable.  Comes in liquid form.

Contact Cement (Neoprene or Styrene-Butadine base)

Solvent flammable unless water based, may be toxic, somewhat water resistant, applied as thick liquid, left to dry 10-20 min., then it bonds on contact; fully cures in 72+ hrs.  Moderate to weak bond strength; not for load bearing applications.  Comes as 1 part liquid.  Used in applying plastic and metal laminates to wood.

Cyanoacrylate Ester (CA Glue or Super Glue, e.g. Krazy Glue™)

Non-flammable, oil, chemical, & water resistant, sets in 5 seconds or less, bonds skin instantly!  Poor shock & peel resistance, consistency varies from watery thin for good penetration to a gel for gap filling.  Comes as 1 part liquid, also available with accelerator & debonder.  Its brittleness can be of use in temporary joints, if it is used sparingly.  More flexible formulations are now available as well.

Epoxy

Non-flammable, may be toxic, waterproof, resistant to most solvents & acid, sets from 5 min. to days, depending on the application.  Strong bond, useful for difficult-to-glue woods or acidic woods, does not shrink, dries transparent to honey colored, hard but not brittle, gap filling.  Unlike many glues, requires little pressure for bonding.  Comes as 2-part liquid.  Mixing ratios vary.  The slower setting epoxies have more penetrating power, and thus have better water resistance.

Hide Glue (Protein Base)

The oldest of the wood glues.  Protein based, non-flammable, not water resistant, liquid form is somewhat heat resistant, also resists most sealers, lacquers, mold, & varnish, sets in 15-20 min., cures in 8-12 hrs.  Strong bond, dries opaque & hard, sands well, stains acidic woods.  Comes as 1 part liquid, or as beads or flakes which are mixed with water and heated to melting.  Useful as the glue in temporary "papered" joints, as it can be heated or steamed to open the joint.  Also used in musical instruments.  The liquid glue made from dry flakes or beads is perishable due to the natural protein content and absence of preservatives.

Hot Melt Glue

Comes in solid form as rods, pellets, sheets, etc.  Heat and pressure required for melting and bonding.  Sets in 30 sec. to 5 min. upon cooling.  Not as stong as conventional wood glues, water resistant, gap filling.  Hot melt polyurethane glues are considerably stronger than conventional holt melt wood glues, which are, in turn, considerably stronger than holt melt craft glues.

Polyurethane Glue (e.g. Gorilla Glue™)

Highly water resistant (urethane glues actually use moisture to dry), but not for prolonged wet-dry-wet cycles.  Resistant to oils and solvents, gap filling.  Very high strength, bonds dissimilar materials.  Dries to clear or a brown color, and expands (foams up) as it dries, thus filling adjacent wood cells and improving the bond.  Somewhat expensive, and messy to clean up (due to foaming).  Requires high clamping pressure (also due to foaming).  Cures in 45 min. to 4 hrs.  Will stain skin, so gloves are highly recommended.

Polyvinyl Acetate Resin (PVA Glue, White Glue, e.g. Elmer's™)

Non-toxic, non-flammable, not water resistant, sets in 45 min., cures in 24-72 hrs.  Strong, but not as strong as aliphatic resin glues; dries hard & clear, does not sand as well as aliphatic resins, not recommended for load bearing applications as it will creep and fail.  Comes in liquid form.

Resorcinol  / Phenol Resorcinol Resin

Completely waterproof, highly resistant to heat, gas, oil, solvents, alkalis, acids, weathering.  Setting time varies with temperature from 10 hrs. @ 70° to 3 hrs. @ 100°F.; do not use at temperatures below 70°F.  Very strong bond, good gap filler, sandable & paintable, dries to a very dark red color.  Comes as 2 parts: liquid & powder.  The sale of resorcinol is now banned in the state of California, due to the formaldehyde fumes produced.  Substitutes include epoxy and polyurethane glues for their waterproof qualities, or Franklin Titebond™ Original (red label) for its strong, creep-free bond.

Urea-Resin (Plastic Resin) / Urea Formaldehyde

Resistant to water, oil, gas, & many solvents, sets in 3-7 hrs.  Very high strength, non-staining, dries light tan to black.  Comes as powder, mix with water to form a cream.  Sale of plastic resin glues is banned in California, due to the formaldehyde fumes.  Substitutes include epoxy and polyurethane glues for their waterproof qualities, or Franklin Titebond™ Original (red label) for its strong, creep-free bond.

Other Glues:

Albumin Glue / Blood Glue (Protein Base)

Made from blood and casein, not as strong as animal glues, more moisture resistant than hide glue, doesn't resist mold or fungi, typically used in cheap plywood construction.  Powder mixed with caustic chemicals and water.

Construction Adhesive (Elastomeric Mastic)

Solvent or water base, low bond strength which builds slowly over weeks, must be nailed to reinforce joint and hold while adhesive sets.  Moisture resistant, gap filling, flexible.  Comes as thick paste (caulk).

Casein Glue / Protein Glue (Protein Base)

Milk-based, non-flammable, water resistant, grease, gas, & oil resistant, sets 15-20 min., cures 8-12 hours.  Dries opaque, sands well, stains acidic woods, good gap filling, useful on oily woods.  Comes as 1 part powder.

Isocyanate

High bond strength, waterproof, bonds wood, plastics and metals well.  Working and cure times vary.  Used mostly in industrial applications such as making flakeboard.  Comes as 2-part liquid; requires high pressure and ,usually, heat to cure.

Soybean Glue (Protein Base)

Made from soybean cake, better water resistance than most vegetable pastes and better adhesive power, but lower water resistance and bond strength than hide glue.  Sometimes used in plywood construction.  Powder mixed with caustic chemicals and water.  May be blended with blood glue for better properties.

Tapioca Paste / Vegetable Paste (Starch Base)

Starch glue.  Used in cheap plywoods, postage stamps, envelopes, & labels; quick tack & cheap, but low bond strength and the glue deteriorates.

References:

Pocket Ref, Thomas J. Glover, Sequoia Publishing, 1989

Cabinetmaking - The Art of Woodworking Series. Time Life Books, St Remy Press, 1992

The Encyclopedia of Wood, U.S. Dept. of Agriculture, Skyhorse Publishing, 2007