A friend of mine claims that porous (very slowly deflating) tires with inner tubes can be treated by the following procedure:

  1. Let the air out.
  2. Elevate the bike so the tire is of the floor (no external pressure on it).
  3. Use a spray-can with silicon grease spray to spray a fair dose of silicon in the nipple. (EDIT: Dunlop/Woods valve with the valve-stem removed.)
  4. Spin the wheel to distribute the silicon and wait 5 minutes to let it dry a bit.
  5. Repeat step 3-4 another 2 times to get the silicon evenly spread along the inside of the inner tube.

The rationale is that the silicon coating will seal the porous rubber from the inside.
(And needs to be applied 2-3 times because the first dose will stick to much to the inside close to the nipple, so it won't make it all through the tire. The 2nd/3rd dose will propagate further as it travels past the area already coated.)

This sort of makes sense at first glance....

Fact of fiction ? Whats your take on this ?

  • 5
    I find that slowly deflating inner tubes can be very easily treated by throwing them away and buying a new one. I have had 100% success with this approach.
    – brendan
    Commented Jan 4, 2017 at 12:05
  • 4
    @brendan Me too. A new inner tube is often cheaper than a can of silicon spray :-)
    – Tonny
    Commented Jan 4, 2017 at 12:23
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    It might possibly work, depending on the variety of spray used (there are several different compositions of such sprays). It would make more sense, though, to use a purpose-made product, or simply purchase less-porous tubes. Commented Jan 4, 2017 at 12:59
  • 2
    Depending on what propellent/solvents are in the grease spray, I could see this even weakening the tube. The MSDS for WD-40 brand silicone grease (wd40company.com/files/pdf/sds/specialist/…) says it contains both a petroleum solvent and a butane/propane propellent. Generally speaking, hydrocarbons are bad for rubber and something I wouldn't want to spray directly into my inner tube.
    – Jamie A
    Commented Jan 4, 2017 at 15:54
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    @JamieA That was my main concern as well. And I know that is the specific brand of silicone spray he would use...
    – Tonny
    Commented Jan 4, 2017 at 16:04

2 Answers 2


Honestly? Sounds like crap.

Here's what proper tyre sealants look like in action:

enter image description here

The latex mix is pushed through a hole and as it passes to the lower atmospheric pressure, the liquid comes out and leaves the salt/latex material in a clump to seal the hole from the inside, which looks like this.

enter image description here

Instead, Your friend has managed to merge the concept of tyre sealant products like Stans or Slime, with canned silicon.

enter image description here enter image description here

Your friend's advice also says nothing about valves. So if you tried to spray through a schrader valve, you'll get exactly nothing in the tube and all the silicon will be on the valve stem. Spraying around a presta valve might get some small amount in if the cap was opened. Instead the advice should have said to remove the valve completely using a valve tool for schrader, or a small spanner for presta.

Next, the bulk of the silicon will pile up on the inside of the tube, straight opposite the valve. It won't "flow" around the inside of the tube much at all.

So my suggestions instead would be

1) Buy a new tube. They're cheap. Just buy one if yours is loosing air. Stick your old one in the saddle bag as a "get-home spare"

2) If your tyres are balding or have gashes, or you can see the threads, buy new tyres. Buy two if you can. This won't really help leak down but will reduce punctures.

3) Optionally remove the valve stem and squirt in some tyre sealant for piece of mind.

Note - some bikes don't even have tubes. Instead they run a setup called "tubeless" where the tyre does all the job of holding the air pressure. These tyres do need sealant added as best-practice.

  • OTT on the pictures? Do the two sample products enhance the answer? By showing they're liquids not gas cans perhaps?
    – Criggie
    Commented Jan 4, 2017 at 10:05
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    As for the valves. He only deals with Dunlop/Woods valves and obviously removes the valve-stem before spraying the silicon in.
    – Tonny
    Commented Jan 4, 2017 at 12:24
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    Note that the OP is discussing "porous" tubes which contain no holes but which leak down rapidly. For these the sealant used need not be as thick and gooey as the anti-thorn variety. Of course, replacing the tubes would make more sense. Commented Jan 4, 2017 at 13:02

Fact or fiction? I have no idea.

I can offer this experience from the last millennium:
When using tubs (singles aka tubulars), they were a pain if they had a slow leak. The effort involved in repairing them never seems worthwhile while the tire is still semi-functional, so we would add a little milk along with the air when inflating it.

It certainly worked, but I can only speculate on how it blocked the leak. I can report that any air that escaped smelled awful.

Could the silicon grease idea work? Maybe. Test it, and report back.

  • That's a new one on me. Somehow there's always more disgusting ideas out there to turn my stomach of a morning. Thanks, Andy.
    – Móż
    Commented Jan 4, 2017 at 21:55

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