Adhesion is best on sanded steel surfaces (2,5 SA). If blasting is not possible the surface should be rubbed with very coarse sandpaper. Do not use Briosil primer on smooth steel, as there is a greater risk of complete loss of adhesion after heating. Iron or zinc phosphatation isn’t recommendable either, as loss of adhesion occurs at 400 °C.
The Briosil primer is not to be used on corrosion resistant steel either. See also the FAQ about stainless steel.