Nylon is ideal for acrylic paint. Flecto Varathane is a good one. I like the semi-gloss finish. I've been making floorcloths for several years now, and nothing makes an apartment look groovier. In one day, you can have the best-dressed floors in the neighborhood, and discover a new creative outlet.
Size matters Art stores carry both primed and unprimed canvas.
Let the cement dry for a while before you press the edges together. The fun part begins. Maybe you want a border, or a diamond pattern. Measure the geometric design if you decide on one, and mark it with a coloring pencil. Keep your brushes wet.