My early customs had base-coats of painted-on gesso, but as soon as I discovered the joys of spray primer I abandoned my gesso for this fast, smooth, easy alternative. Recently I’ve only dug out the gesso for use in making messo to use for wrinkles and veining.
There is one situation in which I prefer gesso as my primer, and that is when the model in question has a textured coat (such as many Schleich and Safari horses or the Breyer Stablemate Donkey). Unless you want to spend hours sanding, customization of these models requires embracing all of their fuzzy glory.
The main reason I quickly moved away from gesso is because the application left the model with brushstrokes and showed plainly under pastels. But when you’re starting with a textured horse, brush strokes in gesso can enhance the existing texture and add further hair detail while still providing a nice base coat. Plus, you avoid the smelly spray primer, which is always nice.
It’s lovely to not have to worry about brush strokes as you work. The only thing you really need to remember is to reflect the hair patterns- you want most of your brush strokes to go vertically down the horse, not horizontally, always following the hair growth around areas like the flank and belly. The muzzle should be smoother to reflect the shorter, softer hairs, and of course the hooves should be as smooth as possible.
Like spray primer, gesso is sandable when dry, so don’t be afraid to redo an area if it looks wonky. Gesso texture will show under pastels, so make sure you like what you see before you start adding colors.