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138 ASSEMBLY TECHNIQUES

As its name implies, this adhesive is designed to bond more or less instantly on contact.
This is accomplished by applying a thin layer of the cement on one or both surfaces to be
joined, then briefly waiting for the cement to partially set up. Applying pressure to the joint
aids in creating a strong bond. Popular contact cements include Weldwood and Fastbond.

Solvent Cement
Solvent cement uses a chemical that dissolves the material it is bonding. It can be tricky to use
because if the solvent isn’t precisely matched with the material, nothing happens!
The most common solvent- based adhesive is for bonding PVC irrigation pipe, which can
also be used with expanded PVC sheets, detailed in Chapter 9, “Working with Plastic.” Other
solvent- based cements are available for ABS plastic, polycarbonate, acrylic, and styrene.

APPLYING HOUSEHOLD ADHESIVES
With very few exceptions, household adhesives (those grouped above, at any rate) use
single- part chemistries, so there is nothing to mix. Just open the tube, can, or jar, and apply
the adhesive to the surfaces to be joined.
• Use all adhesives sparingly. A common mistake is to think that if a little bit of adhesive will
do the job, a lot must be better. In fact, the reverse is true.
• For adhesives with a watery consistency, apply with a small brush or cotton- tipped swab.
For thicker consistencies, apply directly from the tube or with a wooden toothpick or a
manicure (orange) stick.
• Very few adhesives will stick to grease and dirt, so be sure to always clean the surfaces to
be joined. Household- grade rubbing (isopropyl) alcohol does the trick.
• Avoid moving the glued joint until the adhesive has had a chance to set. As needed, clamp
the or tape the bonded parts together.

ALL ABOUT TWO- PART EPOXY ADHESIVES
When normal household adhesives aren’t enough, you need to turn to the “big guns”: two- part
epoxy adhesives. They’re called two- part because at the time of application you combine a
separate resin and a hardener (also called a catalyst). Separately, these materials remain in a
liquid form. But when combined at the time of use, the hardener reacts with the resin and the
mixture sets quickly. During this process, a bond is created as the epoxy liquid fills pores,
cracks, and crazes in the surfaces of the material.

Why Is Epoxy So Special?
Epoxy sets up relatively quickly, generally in from 5 to 30 minutes. Epoxy tends to be a thick
and gooey adhesive, so it has good gap- filling qualities. That’s great for assembling parts that
don’t quite fit together. And epoxies can bond to many surfaces, including paper, wood,
metal, fiberglass, most plastics, and fabric.
The typical package of epoxy adhesive consists of two tubes or bottles: one is the resin,
and the other is the hardener. The tubes are separate in some products, and in others they are
joined as one unit, with a single “plunger” in the center for accurately metering the resin and
hardener. Figure 13-9 shows a typical plunger- style tube applicator. These are a lot easier to
use than the two- tube products.

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