In this painting I had major problems laying down multiple coats of plaster and when I sanded through to the previous coats it looked Splotchy....spotted....you coud tell it was a previous coat. It is mos noticiable on the ladies umbrella, and sidewalk. I quess I am asking for advise on blending multiple layers of plaster and sanding through them to bring out the details of the previous layers I have laid down....Please Advise