How To Flatten Painted Cardboard. This is especially pronounced with the cheap cardboard panels simply because they are if not you are kinda out of luck and will need to try to flatten it with books and perhaps a little heat. If you've created a painting on a piece of paper and are experiencing buckling or waviness after it has dried, we've got two methods you can try to flatten it. When using cardboard for art projects, which types of paint can you use on cardboard?
Painting on cardboard is the real thing;
Cover a work surface with newspaper, setting the box atop the paper. However, unlike the sheets of paper you can paint water colors on, bare cardboard isn't especially suited for lasting painted finishes. Notice that in the flattened artwork some areas turned into pixels. To paint on cardboard, use either acrylic or spray paint. Cover a work surface with newspaper, setting the box atop the paper. If your rug still won't lie flat, apply some heat to it. This is especially pronounced with the cheap cardboard panels simply because they are if not you are kinda out of luck and will need to try to flatten it with books and perhaps a little heat. Cover the back of the poster with a normal cotton sheet and set.
