Gesso over Pastel and Colourfix?

[Brenda Ellis]

I've got a hardboard panel (24"x36") that I had primed with ArtSpectrum Colourfix Primer. i started a sketch for a pastel on it, but have sinced changed my mind and want to use it for an oil painting. I know that Colourfix can be used as a base for oil paints, but I am concerned about the ghost remains of the pastel drawing underneath. (It's just a line drawing of a head and torso.) Do I need to remove every last trace of pastel before I re-prime the board? I will probably use acrylic gesso to reprime it.

I'm thinking I could sand it very thoroughly and get most of the pastel off. I am wondering about washing it with a wet (water) rag?

I am assuming that acrylic gesso would be okay over Colourfix Primer.

It's not as simple as just going and buying another board. I am one of those fabled starving artists.

Any suggestions? Will it be okay to sand it and then wash it and then reprime with gesso and not worry about minute traces of pastel under the gesso?

Also, at this size of board do I need to worry about any sort of support to keep it from bowing? Would gesso-ing both sides help keep it from bowing?

Am I worrying too much?