Gluing Wood Together

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Gluing Wood Together

Choose the right glue for your wood and joint

by Bob Duncan

 

Two factors contribute to the success and longevity of a glue joint: the gluing process and the type of glue. To explore the types of glue used in woodworking, read on.


 The Gluing Process

Flat Surfaces and Clamping

Glue molecules bond only with wood, not with other glue molecules. The tighter the space between the boards, the stronger the joint will be. Because smooth, flat pieces will fit together more tightly, make sure the wood is smooth and flat before joining. Use clamps when gluing to reduce the space even more. Apply enough glue to cover the surface, and clean up any squeeze-out before you finish the project.

Finishes and Oily Woods

Raw wood glues best to raw wood, so for the strongest glue joints, glue the pieces together before applying any finish, or use tape to mask off the areas that will be glued. Naturally oily wood, such as teak or ebony, does not bond well. Before applying glue to these types of wood, wipe the mating surfaces with acetone and quickly apply the glue and clamps.


 Types of Glue

PVA Glue (Elmer’s Wood Glue, Titebond I, Titebond II, Gorilla Wood Glue, Aleene’s Tacky)

PVA glue makes a strong joint between two porous surfaces, like wood, and therefore is the most common adhesive used by woodworkers. Yellow wood glue is more water resistant than white wood glue, but none of these glues are waterproof. PVA glue is not good at filling gaps. Tacky glue tends to be thicker than wood glue, and it gets tacky faster, but it does not create as strong a bond.

Cyanoacrylate (CA) glue

  • Standard CA glue (Super Glue): Cyanoacrylate glue lacks the strength of wood glue but dries much faster. This glue was designed to bond everything from wood, ceramics, and fabric to metal and plastic. A CA glue bond is strong if you try to pull it apart (remember the commercial with the man dangling from his helmet?), but the bond is weak if you apply sideways pressure. Some CA glues fill small gaps, but you sacrifice strength for the gap-filling ability. Some newer CA glues have rubber mixed in to create a more flexible joint. CA glue can be a good choice for fretwork projects or to quickly connect pieces while stronger glue sets, as for intarsia projects.
  • Nexabond 2500: A company called Bioformix has designed a new CA glue specifically for woodworking and claims this glue is stronger than white glue. Ordinary CA glue contains water, which causes wood to swell slightly when the glue is applied. As the wood dries, it shrinks. This expansion and contraction weakens the joint. Nexabond 2500 removes the water to eliminate the wood movement and make a tighter joint. It’s comparable in price to other CA glues and sets up as fast.

Polyurethane Glue (Original Gorilla Glue, Elmer’s Polyurethane, Titebond Polyurethane)

Polyurethane glue uses moisture to activate a sticky foam joint. This glue fills gaps and is waterproof, but, according to a test by Fine Woodworking magazine, is not as strong as PVA glue. Polyurethane glue is also messier than PVA glue because you must apply water to the two surfaces and the glue creates foam as it cures. You must clamp these joints tightly; the foam can actually push the joint apart.

Epoxy and Silicone Glues (5-minute epoxy, JB Weld, Goop, E6000)

If you need to join wood with some other material, you have a gap to fill, or you need to join end grain with something, use silicone or epoxy. They are not as strong as other glues in tight joints, but they are much stronger when used on gaps, end grain, or non-porous material. Silicone glue often contains harmful chemicals and does not smell good. Most epoxies must be mixed before using.


This article was first published in Scroll Saw Woodworking & Crafts Holiday 2013 (Issue 53).

 

 

 

 


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