A buddy of mine used Por15, was chipping away about a year later, it was like it was rock hard. Wasnt empressed, I been useing this stuff since its been on the market, sold only by Eastwood, Rust Encapsulator, Stuff is awesome, you dont even have to blast, I spray though a gun, spray paint over the top with stuff, let it sit for a couple of days , scuff then start with your primer, awesome stuff for rust
http://www.eastwood.com/rust-encapsulator-4.html