After cleaning up all the sanding dust, etc, it was time to prepare the surface for painting. I checked my Artist Handbook about preparing Masonite. So the first job is to wipe down the whole surface with a rag soaked in Methylated spirits, to wash all handling greases and tannin of the surface. The metho dried very quickly.
Now it was time to start using a paint brush, finally - which I enjoy using. I noticed after the first coat of white acrylic primer, the tannin in the Masonite was getting soaked into the white paint, leaving a discoloration - like old paper. I had to wait a few hours before applying another coat (three coats in all).
The next morning I applied three coats of heavy acrylic Gesso, with a light sanding in between coats. It is all starting to look as good as I hoped it would. "Thank you God".