|Why I Gesso Everything First|
Gesso is an acrylic primer and an excellent base coat to assure your paints will adhere to the surface.
I paint on both canvas and paper. Canvas typically has a thin coat of acrylic gesso that has already been applied when you purchase it. Regardless, I still apply a base coat of gesso. I get "ownership" of the surface with plenty of brush strokes and texture. Utrecht Professional Gesso is my favorite. It is the best, yet affordable. Less expensive gessoes are very problematic - either too gritty, runny, plus acrylic paints tend to flake off the painting surface.
The real reason I prime every substrate is no matter what I paint on, the reaction and results will be the same. I literally trowel the thick gesso on EVERYTHING, one side only. Let dry. Then begin painting.
Plus, my paint does not "absorb" right away into the surface, thus more time to move my paints around because I sealed the surface with acrylic gesso.