7.3: Adhesives and Basic Glue-Ups

7.3 Adhesives and Basic Glue-Ups

Most woodworking projects eventually reach a point where separate parts must become one assembly.

In WMT 101, the primary adhesives used are Titebond Original and Titebond III.

Both are woodworking glues in the PVA family and are appropriate for many common solid-wood assemblies.

Later woodworking courses may introduce other adhesives for more specialized applications.

Learning Outcomes

After completing this section, you should be able to:

• Explain the basic purpose of woodworking adhesive.
• Identify the two primary glues used in WMT 101.
• Recognize several common adhesive types used in woodworking.
• Prepare parts for a successful glue-up.
• Explain the importance of dry fitting, clamping, alignment, and cure time.

Adhesives Used in WMT 101

Titebond Original

Titebond Original is commonly used for interior woodworking assemblies.

It is useful for many:

• furniture joints;
• edge-to-edge glue-ups;
• frame assemblies; and
• general classroom projects.

It develops strength relatively quickly and is easy to use for typical indoor woodworking.

Titebond III

Titebond III is another PVA woodworking adhesive.

It provides greater water resistance than standard interior woodworking glue and has a somewhat longer working time, which can be useful for assemblies requiring more time to position and clamp.

In WMT 101, your instructor will specify which adhesive is appropriate for the project.

Other Common Woodworking Adhesives

You may encounter other adhesives as you continue in woodworking.

Adhesives and their uses

Adhesive Type	Common Uses
PVA woodworking glue	General furniture, cabinet, and solid-wood assembly
Polyurethane glue	Some moisture-resistant and mixed-material applications
Epoxy	Gap-tolerant bonding, repairs, difficult materials, specialty work
Cyanoacrylate (CA)	Small repairs, quick positioning, jigs, and specialized applications
Contact adhesive	Laminates and surfaces that must bond immediately on contact
Hide glue	Traditional furniture work, restoration, and specialized assembly
Hot-melt adhesive	Temporary holding, jigs, patterns, and some nonstructural applications

You do not need to master all of these in WMT 101.

The purpose of this table is to recognize that different adhesives are designed for different jobs.

Do not substitute an unfamiliar adhesive without understanding its properties and receiving instructor approval.

Dry-Fit First

Before opening the glue bottle:

Assemble the project without glue.

This is called a dry fit.

During the dry fit, confirm:

• all parts are present;
• joints fit properly;
• clamps fit where needed;
• the assembly can be brought square;
• you understand the assembly order; and
• you can complete the glue-up within the available working time.

Glue-up is not the time to discover that a part does not fit.

Prepare Before You Apply Glue

Before starting:

1. Arrange the parts in assembly order.
2. Gather the required clamps.
3. Prepare cauls or blocks if needed.
4. Have measuring and squaring tools nearby.
5. Protect the work surface when appropriate.
6. Make sure the mating surfaces are clean.
7. Review the assembly sequence.

Once glue is applied, the available working time becomes limited.

Preparation reduces unnecessary rushing.

Apply Enough Glue

Apply enough adhesive to create a thin, continuous film across the mating surface.

The goal is complete coverage.

Too little glue can leave dry areas.

Too much glue creates unnecessary squeeze-out and cleanup.

Do not use extra glue as a substitute for poor-fitting parts.

Spread the Glue

Spread the adhesive evenly over the intended bonding surface when necessary.

Pay particular attention to:

• edges;
• corners; and
• areas that may have received too little adhesive.

The entire intended glue surface should participate in the joint.

Assemble the Parts

Bring the mating pieces together while the adhesive remains workable.

Make sure:

• joints are fully seated;
• parts are aligned;
• reference faces remain flush; and
• the assembly has not shifted while clamps are being added.

Clamp Pressure

Clamps hold the pieces in close contact while the adhesive cures.

The goal is firm, even pressure.

More clamp pressure is not automatically better.

Excessive pressure can:

• distort an assembly;
• damage soft wood;
• cause joints to shift;
• bow parts; or
• squeeze out unnecessary amounts of adhesive.

Use enough pressure to bring the mating surfaces into full contact.

Clamp Placement

Place clamps so the pressure supports the intended shape of the assembly.

Whenever possible:

• distribute clamps evenly;
• place pressure near the joints;
• alternate clamp positions when useful; and
• watch for parts being pulled out of alignment.

More clamps are useful only if they are helping.

Cauls

A caul is a temporary piece used to distribute clamp pressure or help maintain alignment.

Cauls may be used to:

• keep surfaces flush;
• spread pressure over a larger area;
• protect the project from clamp marks; or
• help keep an assembly straight.

Not every glue-up requires cauls, but they are useful tools when an assembly becomes more complex.

Check Square Before the Glue Sets

After applying clamps, inspect the assembly.

Check:

• squareness;
• alignment;
• flatness;
• joint closure; and
• overall dimensions.

For rectangular assemblies, comparing the two diagonal measurements can help determine whether the assembly is square.

If the diagonals are equal, the assembly is generally square.

Make adjustments while the adhesive is still workable.

Squeeze-Out

A small amount of glue appearing at the joint line is normal and usually indicates that adhesive coverage reached the edge.

Large amounts of squeeze-out often mean more glue was applied than necessary.

Follow your instructor’s demonstration for the appropriate cleanup method.

The important point is that cured glue left on a visible surface can interfere with sanding and finishing.

Allow the Adhesive to Cure

Do not remove clamps simply because the glue has stopped looking wet.

Adhesives require time to develop strength.

Follow:

• the adhesive manufacturer's instructions;
• the conditions in the shop; and
• your instructor's directions.

Temperature, humidity, wood species, joint type, and adhesive type can all affect working and cure time.

When in doubt, allow more time rather than less.

Glue-Up Sequence

A basic glue-up can be summarized as:

Dry-fit → Prepare/Adjust → Apply glue → Assemble → Clamp → Check → Clean up squeeze out → Cure → More Clean up/Touch up

The actual procedure will vary with the project, but the principles remain similar.

Professional Habit: Slow Down Before the Glue Comes Out

The best glue-ups often feel uneventful.

That is usually because the work was done beforehand:

• the parts fit;
• the clamps were ready;
• the sequence was understood; and
• the problems were solved during the dry fit.

Good preparation makes glue-up controlled rather than frantic.

Check Yourself

1. What two woodworking glues are primarily used in WMT 101?
2. Why should an assembly be dry-fitted before gluing?
3. What should the glue film look like on the mating surface?
4. Why is excessive clamp pressure unnecessary?
5. What is a caul?
6. Why should squareness be checked immediately after clamping?
7. Why can dried glue create problems during finishing?
8. Why should adhesive cure time not be rushed?