How to make a canvas floor cloth
Shrinking & Priming the Canvas
Purchase #10 weight canvas from a fabric store, craft store or art supply store.
Cut out your canvas quite a bit larger than the size of the finished mat to allow for shrinkage.
Staple the canvas to a wood stretcher frame. Using a sponge and hot water, wet the canvas all over. As it dries, it will shrink. Once dry, apply one coat of primer (latex or acrylic gesso) to the underside of the mat and two coats of primer to the top of the mat. Sand between coats of primer and, as well, sand the final coat of primer so that there is a nice smooth finish on which to paint.