Acid 8 is a linking coat which works in a similar way to Tie-Coat but dries in approximately 2 hours.
Application over cured POR-15 Rust Preventative Paint with a light coat, .allow to dry and then most paints / fillers can be applied directly onto it.
This saves sanding the hard POR-15.
It's available in either the handy 450 ml aerosol or 1lt normal cans.