Hi, I am painting my bathroom that currently has a bright Benjamin Moore semi-gloss paint. I want to paint the bathroom with Tallow. I told the woman at the Farrow and Ball store what I was painting and she brought out a gallon of what she said was the correct primer for using with Tallow in a bathroom (the white & light tones wall & ceiling primer and undercoat). I am having a terrible time with the primer. It seems very thin and is not covering the green very well. Does it not work over semi-gloss? I had washed the walls, should I have sanded them? I read all through the Farrow and Ball website for information and instructions on using their paint before I started and I did not see anything about this. I'm afraid to put the paint on--I feel like I need another coat of primer, which seems crazy!

Thanks for any help or information.