Many people use Masonite or birch boards rather than canvas for painting supports. Usually, artists use boards because they desire a smooth surface, allowing for great detail. But sometimes there may be a reason to create a textured surface for interesting and unusual effects. One way I have discovered to do this is by using a foam roller, purchased from the hardware store, to apply the ground or "gesso". By varying the amount of gesso used, it is possible to create rather interesting and useful textures. Sometimes, gesso that has become "stiff" will result in small craters on the board - interesting to experiment with. As an aside, it is probably good practice to use a board as support for canvas, to reduce the flexibiliy of the canvas which can lead to problems with paint cracking.