I obtain one sq. foot 'Peel N' Stick' floor tiles at close-out sales. I apply two coats (four for oil painting) of gesso (or "Kilz" primer) for acrylics. I sand after each coat. I take cardboard and spray both sides with 'Loctite' adhesive (to preserve the carboard) and allow to dry. I adhere the floor tile and press.
This can be cut in sections as desired. It is an inexpensive platform for beginning artist and those wishing to carry out a study.