Just about anything can be decorated using découpage. Découpage consists of covering something with paper or fabric pieces using a paste or gel that adheres and seals the pieces on the object. Découpage paste is both an adhesive and finish. Even uneven surfaces can be decoupaged. Dampening the material that you are decoupaging the surface with will allow it to form better around the uneven surfaces of the object. Experiment with different surfaces and you will be surprised at the different effects that you can achieve. For example, you can achieve a painted effect by decoupaging magazine or art clippings onto slate.
Place the object with the uneven surface on a work surface. Coat the object with an even coat of découpage paste using a foam craft brush. You may need to do one part at a time to avoid the object sticking to the work surface. For example, if you are doing a box, you would have to do the exposed sides, allow them to dry and do the remaining side.
Dampen a sponge in a tray of water. Dab the pieces of paper with the sponge to dampen them as you apply them to the uneven surface. Press your fingers over the paper as you press them in place to smooth them over the uneven surface. If the material is still not adhering smoothly over the uneven areas you can go over it with a damp sponge and continue to work it over the surface with your fingers.
Brush over the top surface of the paper pieces with découpage paste. Allow the paste to dry for at least four hours. If you don't have other areas that you need to découpage on the object then you can apply a second coat. If you had areas that needed to be flipped, you will need to flip the object and follow Steps 1 through 3 to découpage it and allow it to dry for at least four hours. You may then apply a second coat to the first side, allow that to dry and repeat the process for the remaining side.
Découpage paste comes in matt and gloss finishes. You can experiment with the different finishes to achieve different effects. You can also achieve different effects by using different brush strokes to apply additional coats of paste. One example would be to use a cross hatched pattern similar to a finish on a painting.