Mixing Mud for Skim Coat

why not use a glazing putty like Icing,Half-Time,Dolphin,Metal-Glaze,e.t.c. there are dozens of them, none will have sticky surface if mixed properly and they are made just for that, to skim over pinholes and scratches,

I would not take a chance of mixing not enough hardener or adding some junk into the filler and year later have problems showing in the paint