A drawing surface should be flat, smooth, without dents or scratches. So I bought an 18 mm thick sheet of plyboard to prevent warping and cut it to 18 x 600 x 900 mm (3/4 x 24 x 36 inches) allowing for A1 size paper. I sand papered one side to get a near perfect surface before applying a 50:50 mix of turpentine and varnish for a penetrable stable foundation. I re-sanded once dry and applied a coat of pure varnish followed by another three coats between sanding to buikd up a
