Technical question: when I paint on the beach, I usually get a little sand in the paint. At first this was a nuisance, but I came to like the textural change. Are there any negative effects on the permanence of the paint, or anything else? I would like to try a painting with sand mixed in the paint.
Suggest you look at the work of Anselm Keifer, he uses sand and lots of other textures to provide him with his muse.
Yes you can even gesso your canvas with sand as it is inert ..also marble dust was often used by masters when priming canvases. I use it myself to make my own pastel boards and to add texture when i need to.