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SELECTING AND USING ADHESIVES 137

100%

Curing
Setting
50%

Figure 13-8 Adhesives have both a
setting time and a curing time. So- called
instant glues have a short setting time, but
10%
their curing time can be minutes, hours,
1 hr 2 hrs 12 hrs 2 days 5 days 7 days even days.
or paste to a gel or solid. Though the adhesive may look to be “hard” when set, it is not yet
very strong. This requires curing. Setting times for most adhesives are measured in minutes
or even seconds. But curing takes a lot longer— typically 12 to 24 hours (see Figure 13-8), and
often more.
For most adhesives, curing time is greatly dependent on several factors:
• Surface temperature. Warm surfaces tend to promote faster curing. This is most notable
when gluing metal.
• Adhesive volume. The more adhesive that is applied to a joint, the longer it takes to cure.
That’s why you shouldn’t apply too much glue.
• Air temperature. The warmer the air, the faster the curing (and setting time, for that matter).
• Air humidity. Adhesives differ in their affection for moisture in the air. Some, like Super
Glue, cure faster when the air is moderately humid. Others, like epoxy, cure faster when
it’s dry.

ALL ABOUT “HOUSEHOLD” GLUE
The term “household glue” is a large, diverse, and not very accurate way to describe glues that
you’d use for normal household chores, like fixing broken plates or mending a busted chair.
They’re also good for most robotics chores because they’re easy to get, inexpensive, and most
won’t kill you the moment you uncap the bottle.
PVAc
PVAc- based adhesives are among the most popular general- purpose glues now available, and
they are often sold as white and yellow “woodworking” glues. They are water- based, easy to
clean up, and inexpensive. They’re best with porous material, like wood.

Silicone
Silicone- based adhesives are used for both gluing and sealing. They can bond most any non-
porous surface to another, such as metal to hard plastic. A common trait of silicone adhesives
is that they remain elastic. Use only in well- ventilated areas. After use, be sure the bottle or
tube is recapped tightly so that no moisture can enter.
Contact Cement
Contact cement is based on various volatile organic compounds, which I personally can’t tol-
erate without getting a major headache. So I tend to stay away from it. Still, it’s great stuff for
cementing just about anything to anything else.

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