I may have been a bit premature with my praise of POR-15. When installing the seat today I scuffed the POR-15 coat with the seat track and it peeled up easily.
I sent the following email to POR-15:
To whom it may concern-
I recently used the POR-15 series of products on my 1979 Mercedes and am quite dissatisfied with the results. The POR-15 was used on the car’s floor panels as part of a rust repair job following welding in some patch panels. The surface was a mixture of paint, surface rust and bare steel. I cleaned and prepped the areas using Marine Clean and Metal Ready following the instructions on the packaging, then applied three coats of black POR-15 using a brush after through stirring of the product. Several days later when reinstalling the seats in the car one of the seat tracks impacted the POR-15 coating causing it to chip and peel. Further investigation revealed that the POR-15 coat could easily be pealed off with a finger nail. I have attached a photograph of the area. The surface of the area that has peeled is a combination of wire wheeled surface rust and original paint. Unfortunately it seems that the POR-15 did a better job sticking to my skin than the floor panels. Because the POR-15 has formed a “skin” with poor adhesion to the panel it seems that it will provide worse rust protection than standard paint because it will trap water against the metal and hid the rust rather than bubbling up as paint would do. I selected POR-15 because I did not want to worry about these areas rusting ever again, but it seems that I was mistaken.
I'm torn on what to do now. The POR-15 seems to have stuck quite well to the lid, so it is possible it has adhered better in other areas of the floor. I could try removing it but I think it would be time consuming. My other choice is to leave it and keep an eye on it. I am sick of this rust repair job and want the car to be drivable again so I really don't want to spend another month of weekends pealing and re-coating the area.