Latex tubes, Sealant to minimize air loss

I have poked around a bit and have not found any discussion of whether
the slow air loss typical of latex tubes (or overstretched butyl) can
be minimized by using a sealant such as "Stan's," "True Goo" or
"Slime." I realize those are intended for air leaks caused by actual
breaches in the tube (or tire) but am curious how the leakage due to
porosity of an intact tube may be affected.
Does anyone have any experience with this?

DR

Dirtroadie wrote:
I have poked around a bit and have not found any discussion of whether
the slow air loss typical of latex tubes (or overstretched butyl) can
be minimized by using a sealant such as "Stan's," "True Goo" or
"Slime." I realize those are intended for air leaks caused by actual
breaches in the tube (or tire) but am curious how the leakage due to
porosity of an intact tube may be affected.
Does anyone have any experience with this?

DR

Enough sealant to completely coat the entire inside of the tube would
make it like it was filled with liquid...just get the pump out each
morning.

On 20 Sep 2006 06:43:32 -0700, "Dirtroadie"
wrote:

I have poked around a bit and have not found any discussion of whether
the slow air loss typical of latex tubes (or overstretched butyl) can
be minimized by using a sealant such as "Stan's," "True Goo" or
"Slime." I realize those are intended for air leaks caused by actual
breaches in the tube (or tire) but am curious how the leakage due to
porosity of an intact tube may be affected.
Does anyone have any experience with this?

DR

Dear DR,

Slime would probably have little effect on air loss in latex.

Overnight, most of the stuff pools at the bottom of the tube, so most
of the inside of the inner tube isn't coated with it. (As soon as you
pedal off, the wheelspin distributes the stuff around the inner tube
again.)

In any case, it's not porosity that causes latex tubes to lose air.

About 80% of the atmosphere is N2, 20% is 02, and a smidgen is CO2.
(Plus milli-smidgens of a few other rare gases.)

These gases are soluble in both butyl and latex rubber:

http://www.madsci.org/posts/archives...2329.Ch.r.html

As that short article explains, CO2 is about 15 times as chemically
soluble in rubber as N2. That's why tubes inflated with CO2 cartridges
lose "air" so quickly compared to tubes inflated with 80% N2 from a
hand pump.

Just as CO2 is much more soluble than N2, latex is much more
chemically soluble than butyl. So expensive latex tubes lose gases
much more quickly than ordinary butyl tubes. It's not a mechanical
matter of "pores" being larger in latex--it's a chemical process in
which latex is more reactive.

In the process, the gases are attracted to the rubber and are drawn
into it, between its atoms. There's less pressure on the other side of
the tube, so that's where the gas atoms come out of solution.
Eventually, the tire goes flat.

This is why party balloons filled with helium last longer when they
have that shiny metal foil coating. Neither the rubber nor the metal
have "pores" like the pores in our skin, and the size of the gas atoms
doesn't matter. It's just that the gases are chemically soluble in
rubber, but not in metal.

Cheers,

Carl Fogel

I have poked around a bit and have not found any discussion of whether
the slow air loss typical of latex tubes (or overstretched butyl) can
be minimized by using a sealant such as "Stan's," "True Goo" or
"Slime." I realize those are intended for air leaks caused by actual
breaches in the tube (or tire) but am curious how the leakage due to
porosity of an intact tube may be affected.
Does anyone have any experience with this?

In the way-back days, using tubulars (sew-ups) with very thin latex tubes,
the trick was to let some milk sit out for a day or two (turn sour), and
then, using an old frame pump we didn't care about (for obvious reasons),
suck up some of the milk into the pump and then inflate it into the tube.
This actually did seem to help for very slow leaks in latex tubes. Of
course, you didn't want to be around when you had to let the air out of the
tire.

--Mike-- Chain Reaction Bicycles
www.ChainReactionBicycles.com

Mike Jacoubowsky wrote:


In the way-back days, using tubulars (sew-ups) with very thin latex tubes,
the trick was to let some milk sit out for a day or two (turn sour), and
then, using an old frame pump we didn't care about (for obvious reasons),
suck up some of the milk into the pump and then inflate it into the tube.
This actually did seem to help for very slow leaks in latex tubes. Of
course, you didn't want to be around when you had to let the air out of the
tire.

--Mike-- Chain Reaction Bicycles
www.ChainReactionBicycles.com

That one definitely needs to be added to the tubular FAQ. But wouldn't
fresh milk go sour in the tube?

In article ,
wrote:

On 20 Sep 2006 06:43:32 -0700, "Dirtroadie"
wrote:

I have poked around a bit and have not found any discussion of whether
the slow air loss typical of latex tubes (or overstretched butyl) can
be minimized by using a sealant such as "Stan's," "True Goo" or
"Slime." I realize those are intended for air leaks caused by actual
breaches in the tube (or tire) but am curious how the leakage due to
porosity of an intact tube may be affected.
Does anyone have any experience with this?

DR

Dear DR,

Slime would probably have little effect on air loss in latex.

Overnight, most of the stuff pools at the bottom of the tube, so most
of the inside of the inner tube isn't coated with it. (As soon as you
pedal off, the wheelspin distributes the stuff around the inner tube
again.)

In any case, it's not porosity that causes latex tubes to lose air.

About 80% of the atmosphere is N2, 20% is 02, and a smidgen is CO2.
(Plus milli-smidgens of a few other rare gases.)

These gases are soluble in both butyl and latex rubber:

http://www.madsci.org/posts/archives...2329.Ch.r.html

As that short article explains, CO2 is about 15 times as chemically
soluble in rubber as N2. That's why tubes inflated with CO2 cartridges
lose "air" so quickly compared to tubes inflated with 80% N2 from a
hand pump.

Just as CO2 is much more soluble than N2, latex is much more
chemically soluble than butyl. So expensive latex tubes lose gases
much more quickly than ordinary butyl tubes. It's not a mechanical
matter of "pores" being larger in latex--it's a chemical process in
which latex is more reactive.

In the process, the gases are attracted to the rubber and are drawn
into it, between its atoms. There's less pressure on the other side of
the tube, so that's where the gas atoms come out of solution.
Eventually, the tire goes flat.

This is why party balloons filled with helium last longer when they
have that shiny metal foil coating. Neither the rubber nor the metal
have "pores" like the pores in our skin, and the size of the gas atoms
doesn't matter. It's just that the gases are chemically soluble in
rubber, but not in metal.

Rubber has `pores' or at least a labyrinth that allows
for diffusion of the gas molecules. Contrast nylon-metal
film helium balloons. The rate of effusion or diffusion
through the membrane does depend upon chemical affinities.
It also depends on the mass of the molecule, faster for
lighter molecules. Also a chemical affinity for a
particular gas will swell the membrane making it more
permeable. CO2 will diffuse more quicly through rubber
than the lighter He, because of the affinity of the C in
CO2 with the C in the rubber. And the He will diffuse more
quickly than N2 and O2 because it is much lighter, hence
moving faster.

--
Michael Press

Dirtroadie wrote:
I have poked around a bit and have not found any discussion of whether
the slow air loss typical of latex tubes (or overstretched butyl) can
be minimized by using a sealant such as "Stan's," "True Goo" or
"Slime." I realize those are intended for air leaks caused by actual
breaches in the tube (or tire) but am curious how the leakage due to
porosity of an intact tube may be affected.
Does anyone have any experience with this?

I can tell you for certain that my tubulars with latex tubes that I
have used Tufo sealant in have held air better than they did before it.
I can't swear that it's better than a brand new tubular, but it
definitely got better. What happened was something like this timelne:
1. The tire doesn't have a leak, I pump it up every time I use the
bike.
2. The tire gets a pretty big puncture, I fix it with Tufo.
3. I notice that the tire needs less air pumped into it for every use
than it did before the big puncture.

It didn't get me out of having to pump up my tires every morning before
my ride, I just had to pump it up noticeably less. This was with a
small amount of sealant, maybe 10-20cc, IIRC.

At the risk of getting into yet another argument with Brandt, my
experience seems to have been that latex tube tubulars become more
leaky as they are used, in a way I have never noticed with butyl tubes,
hence my uncertainty about whether the tubes hold air better than new
after using Tufo sealant.

Dirtroadie wrote:
I have poked around a bit and have not found any discussion of whether
the slow air loss typical of latex tubes (or overstretched butyl) can
be minimized by using a sealant such as "Stan's," "True Goo" or
"Slime." I realize those are intended for air leaks caused by actual
breaches in the tube (or tire) but am curious how the leakage due to
porosity of an intact tube may be affected.
Does anyone have any experience with this?

It would be much simpler, and less messy, to just get thicker butyl
tubes.
-----------------
Alex

Alex wrote:

It would be much simpler, and less messy, to just get thicker butyl
tubes.

Since I did not describe a goal and merely requested information, what
makes you think that thick butyl tubes would address my concerns,
assuming that I had some and this was not merely an academic exercise?

DR

wrote:

I can tell you for certain that my tubulars with latex tubes that I
have used Tufo sealant in have held air better than they did before it.
I can't swear that it's better than a brand new tubular, but it
definitely got better. What happened was something like this timelne:
[snip]
At the risk of getting into yet another argument with Brandt, my
experience seems to have been that latex tube tubulars become more
leaky as they are used, in a way I have never noticed with butyl tubes,
hence my uncertainty about whether the tubes hold air better than new
after using Tufo sealant.

Thanks. That was exactly the type of "full disclosure" anecdotal
feedback I was looking for. Contrary to the known tendencies of some, I
was not seeking to establish what *should* be happening with an added
sealant.

Actually, all the responses posted so far have help helpful,
enlightening or entertaining. Well, almost all.

Thanks also for reminding me of "Tufo" sealant. I gather it is in the
group of lower viscosity sealants, which SLIME is not.

DR