1You don’t need to understand the intri-cacies of wood’s cellular makeup to bea good woodworker. But knowingabout the basics of wood structure willhelp you produce strong glue joints.

Wood is made up of millions oftiny individual cells, or fibers. Theyvary in type, size, and purpose, but allshare two traits. First, the fibers arehollow. Second, most of the fibers runparallel to the tree stem, meaning theyrun lengthwise in a board.

Take a close look at a board, then,and you’ll see different parts of thosefibers exposed (Illustration, left).

Note that you can clearly see the fiberwalls on the faces and edges of a board.On the ends of a board, though,you seethe open ends of the wood fibers. Asimple way to remember this is to thinkof wood as a bundle of drinking straws.

What it all means to gluing is simple.The faces and edges of a board offer alot of surface area for the glue to bond

with. So these surfaces cansimply be butted togetherand glued effectively.

End grain, though, offersalmost no surface area for theglue to bond with.So an end-grain joint needs more for astrong connection — either amechanical fastener or sometype of machined joinery.

BENCH BASICS | FUNDAMENTAL SKILLS FOR BETTER WOODWORKING

10 TIPS FOR SUPER-STRONG

GLUE JOINTSLearn the right techniques for gluing up joints,

and your projects will go together quickly and

easily — and stay together permanently.

EDGE-T0-EDGE

UNDERSTAND WOOD STRUCTURE

Gluing up a project is anintimidating process formany woodworkers. That’sbecause after many hours

carefully crafting project parts,we knowwe have only minutes once the glue isspread to get everything assembled cor-rectly before the glue sets.And there’sno going back once the pieces arejoined. Many also worry, even after themost successful glue-up, whether thejoints will withstand the test of time.

But instead of being stressful, gluingcan be one of the easiest parts of projectconstruction.You just need an under-standing of what makes a good glue joint,along with how to prepare,assemble,andclean up the project parts afterward.

That’s precisely what we’ll show youover the next few pages.Along the way,you’ll also learn about the three mostuseful types of woodworking glues.Butit all begins with a basic understandingof the material to be joined: the wood.

FACE-TO-FACE END-TO-EDGE

Gluing up anything, from a simple panel to a complex case, will go well if you planahead, dry fit and mark your parts, and haveyour supplies ready when you begin.

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2From Tip 1, we know that end-grainjoints are weak.Yet many projects call forthem. In a door frame, for example, theends of the rails (horizontal members)mate with the edges of the stiles (verticalmembers). If the pieces are just buttedtogether and glued, the joint will fail.

The secret to creating a strong gluejoint is to add surface area.That’s doneby machining the mating pieces to addface-grain to the joints.Several types ofjoints can accomplish this. A few areshown in the Illustrations below.

Half-Lap — One of the simplestways to add face grain is with the half-lap. In this joint, half the thickness ofeach mating piece is cut away wherethey overlap.This forms a strong jointand keeps the faces of both pieces flush.

Mortise-and-Tenon — A mortise-and-tenon is similar to a half-lap in many respects. In this case, a slot (knownas a mortise) gets cut into one of themating pieces.Then, the end of the otherpiece is cut on both faces and edges toform a tongue, or tenon.The mortise-and-tenon offers two advantages overthe half-lap:The glue area is larger, andthe joint is invisible from both sides.

Biscuits — A modern variation onthe mortise-and-tenon is the biscuitjoint. Here, the mortise and tenon arereplaced by matching slots cut in eachmating piece, and a plate (commonlycalled a biscuit) that fits into them.

One notion that’s been around for yearsis that two surfaces that will be gluedtogether should be slightly roughenedup, so the two pieces can get a bit of“bite” on one another. Another mis-conception is that if those surfaces aretoo smooth, all the glue will just squeezeout of the joint when the pieces areclamped together.

As it turns out,both of these ideas aremyths. For a strong glue joint, the twosurfaces to be joined have to be assmooth as possible.

To really understand why,you’d haveto dive further than necessary into the

science of how glues bond. But it’simportant to know that glue bonds ata molecular level,which means the glueand wood actually “fuse” together. Ifthere are gaps between the pieces causedby rough surfaces, this bonding processcan’t happen efficiently.

What you need to do, then, is makethe mating surfaces flat and perfectlysmooth, especially when you’re after a“seamless” joint, such as a glued-uppanel for a tabletop.

To create these smooth surfaces,keepyour saw blades, planer and jointerknives, hand planes, and chisels sharp.

MACHINE JOINTS TO ADD GLUE SURFACE

START WITH SMOOTH SURFACES

By far the most common and usefulglues in woodworking are polyvinylacetate glues (PVAs), most oftenreferred to simply as “yellow glues.”These glues are similar to ordinarywhite glue (school glue) but in amore refined version.Manufacturersgive them names like “wood glue”or “carpenter’s glue.”

When it comes to bondingwood, yellow glues are tough tobeat.They bond with wood fiberson a molecular level to form gluejoints stronger than the wood itself.And yellow glues are the “go-to”glue for about 90 percent of allwoodworking projects.

You’ll find yellow glue in a varietyof formulations from standard gluefor indoor projects to water-resistant,and even waterproof glue.There are also slow-setting versionsthat give youextra time toget complexassemblies puttogether.

Best of all,yellow gluesare inexpen-sive and easyto use.

“YELLOW” GLUES

HALF-LAP JOINT

MORTISE-AND-TENON JOINT BISCUIT JOINT

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Once you spread glue onto your projectparts,you only have a few minutes to geteverything together before the gluebegins to set. So if you find out thatparts don’t fit together properly, or thatyou can’t get everything assembled intime, you’re in trouble.

Thankfully, the solution is easy.Beforeyou spread any glue, assemble the partsdry, without glue.This applies whetheryou’re just edge-gluing several boardsor putting together a complicated pieceof furniture. Always dry-assemble yourproject first.

Most importantly, a “dry run”allowsyou to make sure everything fits togetherproperly, and then fix any problems.

The dry run also lets you work outa logical assembly sequence that willspeed up the actual glue-up.This processoften reveals “sub-assemblies” that shouldbe glued together first.

During the dry run, it’s a good ideato mark each joint with a distinctivesymbol.Then you can just line up themarks during the actual glue-up to ensurethat you don’t accidentally position apiece upside down or backward.

BENCH BASICS

Another debate that commonly arisesabout glue joints centers on how tightlythe joints should fit together.

One side says the joint should haveto be forcibly pounded together. Theother says the joint should slip togethereasily, with just a little “play” to makeroom for glue.

Actually, neither side is right in thisdebate. If the joint is too tight, the gluecan get pushed out during assemblyresulting in a weak joint. If there aregaps between the mating surfaces, on

the other hand, the glue won’t bondwell.Again, this results in a weak joint.

When assembling a machined joint,it should go together with firm handpressure or just a few taps from a mallet.Getting this perfect fit starts long beforethe glue-up begins, with “test joints”to ensure your setups are correct.

With mortise-and-tenon joints, oneother tip helps ensure success.Make thetenon 1/16" shorter than the depth ofthe mortise.This provides space for glueto escape without weakening the joint.

A TIGHT FIT IS THE RIGHT FIT

Most woodworking glues have a shelflife of just one to two years.Glue olderthan that may still work, but it won’thave the holding power of fresh glue.

So, how do you know just how oldyour glue is? Glue manufacturers don’tprint expiration dates on the labels.ButTitebond prints a coded manufacturingdate on the bottle (Photo, right).

To make sure your glue is fresh,don’tbuy more than you can use before itexpires.And write the month and dateof purchase on the bottle.

Also, don’t let glue freeze.This canruin the glue or at least shorten its life.

USE FRESH GLUE

PLAN AHEAD WITH A DRY RUN

Polyurethane glue is the relativenew kid on the woodworkingblock. It works differently than standard yellow glue and can offeradvantages in certain situations.

First of all, polyurethane glue iswaterproof,meaning it can be usedfor projects that sit outdoors.Thistype of glue is also flexible to with-stand climate extremes well.

Polyurethane glue bonds non-porous materials,as well,such as glass,metal, and plastic. So it’s ideal forprojects that include these materials.

Unlike yellow glue,which cureswhen exposed to air, polyurethane

glue cures when exposed tomoisture.That means you’llhave to dampen the woodto ensure enough moisture.

Most of theseglues foam up andexpand a great dealas they cure, too.This causes a lot ofsqueeze-out andcan push apartjoints that aren’tclamped properly.

DECODE THE DATE STAMPTitebond bottles show the year the gluewas made, followed by the month (“A”through “M;” the letter “I” isn’t used).

POLYURETHANEADHESIVES

Last digit of year

manufactured

MonthCode

BatchNumber

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There’s no exact formula for deter-mining how much glue to use in a givenjoint.You can see this by the ambiguousstatements on glue bottles like “coatboth surfaces” or “apply liberally.”

If there’s a general rule, though, it’sthat too much glue is better than toolittle. Excess glue may squeeze out andmake a mess when clamped, but thatbeats a “starved” glue joint.

When applying glue, spread an evenlayer just thick enough to obscure thewood grain, and make sure there are nogaps (Photo, top right). In most cases,coating one of the two mating surfacesshould do the trick.

You’re actually trying to apply justslightly more glue than the jointrequires.That way, when you bring thepieces together and tighten the clamps,a small amount of glue will squeeze outand form a series of small beads alongthe joint line (Photo, bottom right). Nobeads means not enough glue, whileglue dripping from the joint line meansthat you’ve applied too much.

As important as it is to get an adequate amount of glue in a joint, it’salso imperative that you don’t spendtoo much time fussing around whenspreading the glue.Woodworking glueshave a limited amount of working time,

referred to as “open” time, before theybegin to set.For most glues this usuallyaverages about 10 minutes. So you needto work reasonably quickly (though notfrantically) as you spread the glue andtighten the clamps.

VISUAL CUES SHOW THE RIGHT AMOUNT OF GLUESpread glue in a thin, even layer, making sure to coat the entire surface (top). Whenclamped, small “beads” of glue will squeeze out along the joint (bottom).

A LITTLE TOO MUCH GLUE IS JUST ENOUGH

Gluing up a solid-wood panel seemssimple. It’s just a series of straight, squareedge joints.Yet keeping a panel flat andfree of gaps can be challenging.The keyto success is in proper clamp positioning.

To prevent gaps, you need enoughclamps to distribute pressure evenly.Clamp jaws exert pressure at roughly45° angles, and you want the pressure tooverlap slightly (Illustration, left). So forboards 4" to 8" wide,place a clamp aboutevery 8" to 10".Narrower boards requireeven closer clamp spacing. Also, alter-nate the clamps over-and-under thepanel (Photo, left) to keep the panel flat.

Finally, tighten the clamps by eitherstarting at one end and working towardthe other, or starting in the middle andworking toward each end.Tighten themjust enough to draw the joint together.

SPACE CLAMPS EVENLY

Gaps and visible wood grain indicate insufficient glue coverage

Consistent color and an even coatindicate adequate glue coverage.

Look for squeeze-out along the entirejoint line after clamping.

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BENCH BASICS

Squeeze-out is not only inevitable, it’s animportant part of a good glue-up. Butthat means it needs to be removed.Hereagain,we find two schools of thought onhow to best remove this excess glue.

One advocates wiping the squeeze-out away immediately with a damp rag.Often, though,clamps prevent you fromgetting to all of the glue.And it’s easyto push glue into the pores of the wood.This glue residue may not be visibleuntil you apply a stain or finish.

A better way to remove squeeze-outis to scrape it off (Photo, right).Wait untilthe glue beads dry to a rubbery texture

and no longer ooze liquid when youpress on them with a fingernail.

Most yellow woodworking glues willharden adequately in about 20 or 30minutes.And, conveniently enough, thisis about how long you need to waitbefore unclamping the assembly.Thatmeans the clamps won’t get in your waywhen scraping the squeeze-out.

After scraping off squeeze-out,a smallamount of residue may remain.Wait afew hours, and then sand this away.

If squeeze-out hardens completely,use caution to prevent tearing the woodfibers as you scrape off the glue.

SCRAPE AWAY SQUEEZE-OUT

Most of the time, cleaning up squeeze-out is no big deal.But in instances wherethe squeeze-out is hard to get to, you’llneed to take a different approach.

One of the simplest methods is toplace masking tape along the joint linebefore gluing and clamping (Photo, nearright).Any squeeze-out will collect onthe tape, which you can just peel awayonce the glue gets rubbery.

If you absolutely need to preventsqueeze-out, another option that worksin some situations is to cut relief kerfsin one of the mating pieces to catch it (Photo, far right).

STOP SQUEEZE-OUT

SCRAPE ALONG THE GLUE LINEAllow squeezed-out glue to dry untilrubbery (20 to 30 minutes), and thenremove it with a chisel or scraper.

KERFS TRAP GLUETo stop squeeze-out completely, twokerfs are cut into this applied molding.They catch the squeeze-out and stop it.

TAPE TOUGH AREASIn hard-to-reach areas, apply tapebefore gluing. Any squeeze-out willstick to the tape instead of the wood.

EPOXY ADHESIVESEpoxy has long been the adhesive of choice forbonding dissimilar materials and making waterproofjoints and coatings.

Epoxy is made up of two parts: a resinand a hardener.When mixed together,they form an adhesive that is rock hard,waterproof, and won’t shrink.By varyingthe type or quantity of hardener,manufacturers can manipulateeverything from working timeto strength to spreadability.

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