hints on working with liquid latex
Brian Glueck
I'm repairing a bunch of tubular tires and want to use liquid
latex to reattach the base tapes. Can anyone give me any advice
on using liquid latex? How dilute should the solution be?
Thanks,
Brian
Jobst Brandt
Brian Glueck writes:
You shouldn't dilute the latex unless it is too thick to be painted
onto cloth with an expendable brush. The reason for the expendable
brush is that latex sets as rubber on any dry surface it contacts.
Paint the tire and base tape, put tape in place, stretch tire on rim
and inflate hard. When "dry" overnight, you're done.
In case you didn't catch it before, here is an item from the FAQ:
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Subject: 8.41 Tubular Tire Repair
From: Jobst Brandt <jbr...@hpl.hp.com>
Opening the Tire
To patch the tube, you must get into the tire and this requires
opening the casing by peeling the base tape back and unstitching the
seam. If this is a seamless tire, chuck it. There are two types of
seams, zipper stitch (using one thread) and two thread stitch. The
zipper stitch is identified by having only one thread. It appears to
make a pattern of slanted arrows that points in the direction in which
it can be 'unzipped'.
Never open more tire than is necessary to pull the tube out of the
casing. Remember, the tube is elastic and can be pulled out of a
three cm long opening pretty well. Even if there are two punctures
not too far apart, the tube can be pulled out of a nearby opening. If
you must insert a boot, you'll need to open about 6 cm or about the
length of the boot and a little bit more.
Base Tape
Never cut the base tape because it cannot be butt joined. Always pull
it to one side or separate it where it is overlapped. Don't cut the
tire seam, because it takes more time to pull out the cut stitches
than to pull out the thread in one piece. When working on the stem,
only unstitch on one side of the stem, preferably the side where the
machine finished. Use latex to glue down loose threads on a sidewall
cut. Paint the exposed casing zone that is to be covered by the base
tape and the base tape with latex emulsion, allow to partially dry and
put the tape in place. Put the tire on a rim and inflate hard.
Zipper Stitch
Cut the thread at some convenient place at the upstream end of the
intended opening and with a blunt awl, like a knitting needle, pull
out several stitches in the direction the stitch pattern points. When
enough thread is free to pull on, the stitching can be opened like a
zipper. When enough seam is open, thread the loose end through the
last loop and pull tight, to lock the zipper. Don't cut off the free
end because it is often good enough to re-sew the seam.
Two Thread Stitch
One of the threads makes a zig zag as it locks the other thread where
it penetrates the tire casing. Cut both threads near the middle of
the opening and, with a blunt awl like a knitting needle, pull out
only the locking thread in both directions, stitch at a time. The
locking thread is the one that is easier to pull out. Remove as many
stitches as the opening requires. The other thread pulls out like a
zipper. Tie a square knot with the loose ends at both ends of the
opening and cut off the rest.
Patching
Patch butyl (black) tubes using patches from a bicycle patch kit.
To patch a latex tube make patches from an old latex tube that are
fully rounded and just large enough to cover the hole plus five mm.
For instance, a thorn hole takes a 10 mm diameter patch. Use Pastali
rim glue (tire patch glue also works but not as well) wiped thinly
onto the patch with your finger. Place the patch on the tube
immediately and press flat. Latex will pass the volatile solvent
allowing the glue to cure rapidly with good adhesion to the tube.
Casing Repair
Repairing tubular tires requires latex emulsion. You can get it from
carpet layers, who usually have it in bulk. You must have a container
and beg for a serving. If you are repairing a tubular you probably
ride them, and therefore, will have dead ones lying around. The best
tubulars generally furnish the best repair material.
Most cuts of more than a few cords, like a glass cut, require a
structural boot. For boot material, pull the tread off a silk sprint
tire, unstitch it and cut off the bead at the edge of the fold. Now
you have a long ribbon of fine boot material. Cut off a 50cm long
piece and trim it to a width that just fits inside the casing of the
tire to be booted from inside edge of the bead (the folded part) to
the other edge.
The boot must be trimmed using a razor blade to a thin feathered edge
so that the tube is not exposed to a step at the boot's edge,
otherwise this will wear pinholes in a thin latex tube. Apply latex
to the cleaner side of the boot and the area inside the tire,
preferably so the boot cords are 90 degrees from the facing tire
cords. Insert the boot and press it into place, preferably in the
natural curve of the tire. This makes the the boot the principal
structural support when the tire is again inflated, after the boot
cures. If the casing is flat when the boot is glued, it will stretch
the casing more than the boot upon inflation. After the boot dries,
and this goes rapidly, sew the tire.
Tube Replacement
To replace the entire tube, open the tire on one side of the stem, the
side that seems to be easier to re-sew after the repair. Open about
eight to ten cm the usual way, so that the old tube can be pulled out
by the stem. Cut the tube and attach a 1/16" thick nylon cord to the
loose end of the tube to be pulled through the casing as you pull the
old tube out.
Cut the "new" latex tube about 5 cm away from the stem, tie the cord
onto the loose end and pull it gently into the casing. Dumping some
talc into the casing and putting talc onto the tube helps get the tube
into place. With the tube in place, pull enough of it out by
stretching it, to splice the ends together.
Splicing the Tube
This procedure only works with latex tubes. Overlap the tube ends so
the free end goes about one cm inside the end with the stem. With the
tube overlapped, use a toothpick to wipe Pastali rim cement into the
interface. The reason this MUST be done in place is that the solvent
will curl the rubber into an unmanageable mess if you try this in free
space. Carefully glue the entire circumference and press the joint
together by pressing the tube flat in opposing directions. Wait a
minute and then gently inflate to check the results. More glue can be
inserted if necessary if you do not wait too long.
Sewing the Tire
Sewing machines make holes through the bead that are straight across
at a regular stitch interval. For best results, you must use the
original stitch holes when re-sewing. Get a strong thread that you
cannot tear by hand and a (triangular) needle from a Velox tubular
patch kit (yes I know they are scarce). Make the first stitch about
one stitch behind the last remaining machine stitch and tie it off
with a noose knot.
With the beads of the tire pressed against each other so that the old
holes are exactly aligned, sew using a loop stitch pulling each stitch
tight, going forward two holes then back one, forward two, back one,
until the seam is closed. This is a balanced stitch that uses one
thread and can stretch longitudinally.
Now that you know everything there is to know about this, get some
practice. It works, I did it for years.
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