cast iron texure

Ive never done this myself, but having worked with the real thing im guessing a stiff brush used perpendicular to the surface stabbed down to give a bumpy look, then the paint going over top should round it out enough to look realistic. but thats just a guess. correct me if im wrong please guys

Not familiar with Mr. Surfacer but have had good results using auto body filler (Bondo brand) stippled on with a stiff brush.  MEK (methyl ethyl ketone) can be used to thin it if necessary.  You can also use liquid model cement or MEK stippled right into the styrene, sand lightly if the texture becomes too rough.  Last but not least is terra cotta texture spray paint but some feel this gives too uniform a result although it worked out good for the trans cover and mantlet on my M-36 Jackson.

I use the Mr. Surfacer method. I use a small flat brush which by design is stiffer than say a round brush. Keep some brush cleaner nearby as the brusch will get gunked up at times and need to be cleared.

I presume all of the other methods also work which are listed above, The spray on Terra Cotta is great for making the "uniform" factory applied non-slip coating used on modern vehicles.

Rounds Complete!!

Thank you all for replies, I do appreciate the help. Never tried to sim cast iron before.