I tried canvas squares and they did get moldy. I just don't have the
room to lay them out to dry. I have kids work right on the formica.
They have a square of paper for the artwork itself, set lump clay
directly on the formica, roll out coils, etc. I ask them to "snowplow"
the bits of clay onto piles away from the edge. I am fierce about
health issues and they are good about having no clay debris fall on the
floor. Then we wipe down the tables with sponges. I have enough small
sponges that everyone can have a sponge at cleanup time. There are no
footprints on the carpet outside my room. My tables always look great.