A flat tire is always inconvenient, especially if you do not have the money to replace the tire with a new one. The alternative is to have a tire service repair the tire, but some things can affect whether a technician can fix the tire or not.
One of the most common causes of flat tires are punctures that occur when you run over an object like a nail or a screw on the road. The object will often stay in the tread and partially seal the hole so that the tire loses air slowly until it is finally flat.
The puncture location often dictates whether or not a tire repair service or garage can fix the damage. In general, punctures that occur in the tread of the tire are repairable as long as they are at least three-quarters of an inch away from the sidewall. If the hole is very large, and can not be sealed with a single plug, it may not be repairable even if it is within the guidelines, but the technician doing the tire repair will have to inspect the damage to be sure.
If a puncture in the tire will take a plug, but you want to add some extra protection to the repair, the technician doing the tire repair can add a vulcanizing patch to the inside of the tire where the puncture occurred. The plug needs to be put in first, so the patch is not damaged by the plug insertion tool, and the tire needs to come off the rim to place the patch correctly.
Often, tires that have a puncture in the tread that falls into the repairable area, but are a little larger than a standard nail or screw hole, can use the patch and plug method to ensure the puncture does not leak. Some tire repair services will use two plugs in the hole and a patch to ensure a tight seal, but that is not common and requires a knowledgeable tire repair technician to determine if that method will work for your tire.
If your tire suddenly goes flat because of damage to the sidewall, the tire will not be repairable. Tire repair services use plugs and patches to seal a tire after it is damaged. The sidewall of any tire is flexible and does not have the rigidity to hold a plug. Once it is cut, the tire's structural integrity becomes compromised enough that the tire would not be safe to use, even if the tech could patch it.
For more information about tire repair, contact a local auto repair shop.