[header] How to build forms for a curving concrete sidewalk [title] Use 12-inch (30. 5 cm) hardboard siding (sometimes called masonite) ripped down to 6-inch (15 cm) strips in 16-ft. [step] ( 4.8 meter) lengths. ( full-service lumberyards and home centers carry all this forming material. 
) flex it to the desired shape of your sidewalk and stake it down. Use marking paint to mark the ground next to the form.