8b.8 Tube and Tire Casing Repair
Description
This article is from the Bicycles FAQ, by Mike Iglesias with numerous contributions by others.
8b.8 Tube and Tire Casing Repair
From: John Forester <JForester@cup.portal.com>
There sure seems a dearth of knowledge about patching both tubes and
casings.
Yes, the idea that tubes could be patched without liquid cement was a
good idea, but only as an idea to research to see whether an adequate
adhesive could be developed. So far as I know, all the peel and stick
adhesives are very viscous liquids. That means that they don't harden and
therefore that the air pressure will slowly leak into and through them. If
the viscosity is high enough it will take the air under pressure a long
time to form another leak. A glueless patch of the peel and stick variety
cannot have effective solvents in it, because the solvent would evaporate
during storage. Even if the patch were sealed inside a container that
prevented the evaporation of the solvent, the system would have the problem
of getting enough glue onto the tube and then letting the solvent partially
evaporate from the open joint for the joint to be made. You might as well
use the old system.
The problem that some experience is that they find the cement hardened in
the zinc dispensing tube. The answer to that is to buy the cement and its
solvent in bulk and carry a small quantity in a small jar with a screw cap.
A metal jar would be most useful, but I do not know of any common source for
such. Small glass jars are commonly available and last well enough.
Periodically, examine the cement inside and top up with solvent if it gets
too thick. Because the cement tends to glue the cap to the jar, it is
desirable to wrap both the jar and the cap with several layers of adhesive
tape to provide a better gripping surface at a larger radius.
Two kinds of cement are available. The traditional cement is rubber cement,
Camel #12-086 Universal Cement, available at tire shops. The other cement is
contact cement, available from hardware stores. While the modern
formulations often are non-flammable and use chlorinated hydrocarbons as
solvents, buy the flammable kind, if available, because the chlorinated
hydrocarbons are detrimental to rubber. (Very important for diluting rim
cement for tubular tires. Not so important for just tire patches or boots
because the solvent evaporates.) In any case, use toluol as the replacement
solvent, available at hardware stores.
The tube must be cleaned before applying the cement. Stick medium sandpaper
to tongue depressors and cut to lengths that fit your patch kit.
Cut casings are repaired with an internal boot. Satisfactory boots are
made from cotton trouser fabric or from lightweight dacron sail fabric.
These must be cemented by contact cement, not tube cement. Cut pieces of
suitable size, so that they run almost from bead to bead when laid inside
the casing. Coat one side with several layers of contact cement and let it
dry completely before storage. Before applying, coat the inside of
the casing with contact cement and press the boot into place before the
cement dries. Wait about ten minutes before inflating the tire. If you wait
too long, the cement really hardens and there will be a narrow spot in the
casing because of the greater strength where the patch reinforces the
casing.
It is probably possible to use contact cement as the tube patch cement.
Do not use tube cement for boots; it slowly creeps and allows the boot to
bulge. So carry a small jar of each cement, or one of contact cement.
Contact cement is suitable for closing the outside of the cut also, but
it must be applied in several layers and allowed to dry thoroughly before
use, or it will pick up particles from the road. Duro Plastic Rubber is a
thicker black rubber paste that can be applied in one layer and left to
harden.
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