I have a small leak in the roof over my porch. It seems as if a shingle has cracked and I have determined that is causing the leak. Is there a permanent type of roof cement that will work even on a damp surface? It is an asphalt shingle roof. (I think)

The roof isn't even six years old and I am not ready to do a tear-off and replacement.

no there really aren't any permanent roof tar products that you can use to patch your roof...the best bet will be to replace the damaged shingle ...however in the meantime there are products that will adhere to the damp/wet shingle to buy you time...just go to your hardware/home improvement store and look for it in the roofing supplies...it will state clearly on the package that it will work in wet applications

A. Look at the whole roof. If this crack repeats itself multiple times in a roof this young, you have other problems which might include bad product form the manufacturer and need to file a claim against the warrantee.
B. If it is just in one shingle, you can take a piece of metal slip and slide it up under the damaged shingle to back it up byu catching the water that leaks through the crack and shedding it back out on top of the lower course of shingles.
BTW, I have never seen a leak caused by a single crack in a single shingle.

good call, id look for excessive wear on the shingle as well like shedding loads of granules and if the shingles are brittle and hard or worse yet flaking off.

what store has roof batch

I agree with piffin, unless they rolled the last row up the wall, wich is poor application to begin with, that would come right in. Cracking can be traced from poor ventalation and frame movement (stress cracks). Factory defects usually don`t produce cracking. Chipping ice and walking or objects hitting it like ice,trees, ect....do.

Before putting the stepflashing under it, use a garden hose, start at the low points, without wetting above, work your way up in ten minute intervals, waiting for drips between moves. You`ll isolate it !! Please do not attempt this on your roof alone or without expieriance. A professional roofer could.