Auto body repair & detailing: Primer problem, urethane primer, no hardener

Question
While teaching my grandson body work and painting we decided he could mix and spray the primer coats for his grandmothers car.  He failed to mention that he mixed the paint wrong.  He acknowledged he had used the wrong can of hardener (it was actually reducer) and did the last coat with the right hardened.  We have two light coats of urethane with no activator covered with one light coat of activated.  The top coat is hard to the touch but will scrap off with a finger nail.  I feel I know what the answer already is going to be....How do I fix this?  Thanks much, Bill

Answer
Hi William,
     
        I hate to say but you will have to remove the primer. If you paint over it and encapsulate it in, it will gas off and bubble the paint right off when it gets hot. The truth is, even the most experienced painters have done things such as this. Tell him not to get too discouraged and just use it as a life lesson. "Always double check your chemicals before pouring them in." Sorry I don't have better news.