Need to finish sandblasting a get a coat of epoxy primer on the metal before filler work.
Just a suggestion- - - - -it's OK to apply a (thin) temporary prime coat after blasting to prevent surface rust, but be sure to grind back to bare metal before applying any type of body filler. Leave some pretty definite grinding scratches, 40 grit or so, to give the filler some "tooth" to grab onto. Filler applied over primer will lose its grip and fall off.
Jerry
