Self Priming means that quality of paint for which no separate primer is required i.e. that paint can tolerate ill prepared surface ( of course there should not be any loose rust or debrises etc.) by it's special anchorage charateistics by virtue of special additive formulations etc. This class of propert is often called "Mastic" performances. I have list of advantages and probably the basic limitations with this class of paint is slow cure led to and a bit less productivity. Yes you can apply MIO over that . regards DM