After the car's tyre pressure monitoring system prompted me to check the tyres, I did so at a service station. The front right tyre's pressure was about 100kPa lower than the other three. I drove to the workshop, where the mechanic jacked the car up and found a nail embedded in the front right tyre. He then patched the tyre, pumped all four tyres to the recommended pressure and reset the tyre pressure monitoring system.
How is the tyre patching done and how safe is it to continue driving with a patched tyre? Can the same tyre be patched more than once or in several different spots?
Most tyre shops will remove the tyre from the wheel to repair any puncture. They will then clean the puncture area on the inside of the tyre by rubbing it down with a mild abrasive, ensuring there is no foreign object still embedded in the rubber.
The actual patching involves the fixing of a vulcanised adhesive "plaster" over the cleaned area of the puncture hole.
This method of patching is safe enough for use till the end of the tyre's life. There is no harm doing more than one patch on a tyre. In any case, unless you frequently drive on roads littered with sharp debris, you rarely have a tyre going through multiple punctures in its lifetime.
Some tyre shops still use the old method of inserting a solid rubber stud into the hole pierced by the nail. It is quick, does not require the tyre to be removed from the rim and is effective in plugging the hole left by the nail or a sharp object.
Such repair kits are available off the shelf and useful. Although some car owners refuse to allow this method of repair, it used to be the only way to fix a puncture.
In this case too, more than one plugged hole will not reduce a tyre's lifespan.