Diy Wood Flag . Place your 2ft x 4ft plywood backer board on a table. I then marked lines 1” a part all the way to 13”. Burnt wooden American flag by CountryboyCraftin on Etsy Wooden from www.pinterest.ca The top and bottom boards should be red. Remove painter's tape and paint the blue portion of the sign using two light coats of blue acrylic paint. Use your sander to give them a quick sanding.