My wife came home with another nail in her tire today so I patch it again with one of those steelbelted repair patch... you know, one of those sticky black string you push into the hole with some glue and trim the excess off.  This is about 14th time I patch her tires in past year alone.  Front driver side tire was patch about 4 or 5 times now and other 3 were patched atleast once.

Question is, how many times can I repair/patch a tire with this repair kit before I have to replace the tire?  Is the patched spot weaker than rest of the tire?  Every patch has been somewhere along the tread and not on the sidewall.  

I hate to replace them since they cost about $100 per tire and current tires are only about 1 years old and have plenty of treads left but I don't want her to drive around with unsafe tires.
       

Well, I don't have a definitive answer but I've never had a patch fail on my tire.  One tire had at least four or five just like yours.  I think some jacko used to place nails in my tires path of roll.

Anyways, I don't think there's a problem unless maybe the nail falls into the exact same place as a previous one and creates a super hole.

You should have vulcanized patches added on the inside when you have a chance. plugs are good for temp repairs (I have run them along time)  But the
industry says add a patch inside as soon as possible. as long as you keep an eye on the tire pressure often you shouldn't have any problems.
(If your wife runs on low pressure for an extended
period you can suffer thread seperation.)

I don't think there is a limit unless the patches over lap. I too would get it patched from the inside. I would also check the balance soon as well.
And if this is a normal occurace, I would pay the extra 10 bucks for road hazzard and not worry about how many times, as they will replace or repair depending on how safe they think it is.

The correct way to patch a hole in the tread is from the inside. These patches work like the emergency rubber string types but there is also a big 2" round flap attached to it that covers the hole from the inside. Double protection.

I've never had one of those over the counter emergency patches fail. 70+ miles. But I think that it might be time for a new set of tires if there are more than 2 or 3 punctures per tire. Try to see if you can buy a heavy duty tire next time. I think that there are some brands that are highly resistant to punctures.

According to my father--indefinately.  And then you shoot that goop in the tube

Until it stays flat...

I patched and plugged hundreds of tires when I was a station boy in college. Plugs are okay for nails and such. I plugged my own tires many times and never had a problem other than the occasional slow leak. Hell, I had the same plugs in my tires for years. I don't recommend them for jagged punctures, but if the puncture is clean and small, like a nail, plugs are fine.