Auto patch problem advice- opinion needed

[kathy]

Hello & Thanks in advance for any help offered. I really need some info from anyone with knowledge of automotive body repair. Short version of long story: I have a 1991 chevy blazer, with factory sheet metal. I took it in to a shop to be painted w/ very minor body repair. One specific repair was to an 3x5" rust area on the top of cab, in the center of the area the rust went completely thro, causing a line of holes. The repair was to "Cut out rust, Weld a patch". As far as I knew this is what was done. It was not. 5 yrs. pass, the patch begins to lift off. When the patch was removed it was discovered it had been bonded directly on top of the rust with adhesive( 3m duramix) the rust is still bonded to the underside of the patch. I know the area was not prepped properly for either welding or any bonding alternative. My questions are:* IF* the prep had actually been done, how long would either application, welding or bonding of a patch, reasonably be expected to last? What are the pros/cons of adhesive -vs-welding? Again thanks for any assistance.

[kathy]

~I'm sorry, did'nt realize I posted to the wrong Forum~

[Aerometalworker]

Hmmm hard to say. My experience with repairs like that is strictly welding. If the condition the backside of the repair is the same as the factory left it, I would expect the repair to last as long as the original panel did from the factory before the corrosion set in. If the original panel and repair were protected better, and effort was made to resolve what caused the corrosion in the first place, then the patch should last almost forever under normal care.
I would think the same logic applies to bonded repairs.

[kathy]

~Thank-you~