You can't expect to paint a masterpiece on untreated cloth. Here's how to gesso, or prime, a homemade canvas in a hurry. You will need gesso, water, a plastic mixing bowl, a drop cloth, fine grit sandpaper and a house paintbrush. Tip: some painters prefer to use a squeegee to apply gesso, instead of a brush. The edges of your canvas will drip a little, so use a smaller brush to work the excess gesso back into the sides.