This is documentation how do I prepare my gesso boards.
I use MDF or hardboard for large formats. Large formats are glued to a frame to suport it.
I size the surface with 60g/1000g water size solution and use bologna chalk for filler. I cover it with about eight layers and then when dry I scrape them smooth. I dust them with charcoal to see ridges and keep scraping until they are white again and completely smooth.
It is much faster and cleaner than sandpaper, and also cheaper :)