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Tyre repairs: how do tyre sealants work?

By Dan BezerTyre Advice8th August 2019

Tyre sealants are a handy way to keep a tyre running when it has picked up a puncture.

However, they are not fool-proof – and there are some good reasons why you might not want your tyre to run ‘as normal’ if it has been significantly damaged. With a few different options to choose from, it’s also important to know what type of tyre sealant you have.

Here are the main types of tyre sealant and a little more information about each.


Pre-puncture tyre sealant

The pre-puncture tyre sealant is a material that goes into the tyre when it has not yet been damaged, and stays inside ready to go to work if a puncture should ever occur. When the tyre is punctured, the sealant automatically patches over the wound, keeping the air in the tyre so you can continue driving on it.

This is good because it allows you to get to a place of safety before calling in a mobile tyre fitting service like Tyres on the Drive.

The disadvantage here, however, is that you might not notice your tyre is damaged. That can lead to driving on a punctured tyre for long distances, or in the worst cases, blowing out a tyre at high speeds.

Pre-puncture tyre sealants are found inside some new tyres as standard, so if you have one of those, you don’t need to inject your own aftermarket sealant via the valve. Alternatively, you may have a run flat tyre which doesn’t use sealant, but instead has a rigid structure that allows it to travel a limited distance at limited speeds even when flat.


Post-puncture tyre sealant

There are no prizes for guessing what the alternative to pre-puncture tyre sealant is. A post-puncture tyre sealant is designed to be injected after a puncture has occurred. After injecting the sealant – often commonly known as tyre weld – you wait for it to cure, then pump up the tyre again and continue on your way.

The downside to this is the slightly longer delay to your journey while you administer the tyre weld and put the air back in your tyre. But the good thing is that you know for sure if you have a puncture – so you’re not always second-guessing the health of your tyres every time you park up.


How does tyre sealant work?

In both of the above cases, the tyre sealant works by filling the hole caused by the puncture, and then curing, similar to any other kind of glue or filler.

You might be able to see some of the sealant from the outside of the tyre, as it sometimes oozes through the puncture to leave a visible scar on the tyre tread. This will tell you if your tyre is damaged. Then you can avoid driving on it for any longer than you need to.


How long does tyre weld last?

Neither solution should be considered to be a permanent repair. It is just a temporary patch job to get you to a safe place, where you can get the tyre permanently repaired or replaced.

Any permanent tyre repair requires that the tyre be completely removed, checked for structural damage and only refitted if it’s in good enough condition.

Because of this, injecting sealant into the valve or letting pre-puncture tyre weld seal a puncture can never be considered an adequate permanent repair. What’s more, you must always be sure to get the tyre removed and looked at by a professional.

There is also the question of how long pre-puncture tyre weld lasts inside the tyre. If your wheels are several years old, there is the risk that the sealant is past its best and would be unable to fully seal a puncture if one were to occur.


Benefits of tyre sealants

There are some clear benefits of tyre sealants:

  • Complete your journey or find a place of safety on the existing tyre.
  • Pre-puncture sealants activate automatically, preventing delays.
  • Post-puncture sealants can be administered yourself, wherever you are.


As long as you remember that they are only a temporary fix, tyre welds are a relatively good way to continue on your journey following a puncture.


Disadvantages of tyre sealants

The disadvantages are as follows:

  • Not always obvious the tyre has been damaged.
  • Not a suitable permanent repair.
  • Post-puncture sealants still leave a flat tyre that needs pumping up.


One last disadvantage comes if the puncture can be repaired, as filling the tyre with sealant can cause more problems than it fixes. You might have to get the tyre cleaned out to remove the sealant and any remaining residue before you can get the puncture repaired and refitted.


It’s often better to just call out our mobile tyre fitting or puncture repair service and get it done professionally. Contact our team of friendly advisers today by calling 0333 016 6550 or emailing

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