Place strips of Washi Tape slightly longer than the coaster next to one another making sure if there is a pattern on your tape you are matching it.
Once you've completely covered the coaster, press your Washi Tape down so it is nice and smooth on the surface. Flip it over on a cutting mat and, using your X-acto knife, cut the excess Washi Tape as close to the edges as possible.
Take your Mod Podge and foam brush and, following the instructions on the back of the Mod Podge, coat the tops and sides of the coasters and let dry. When they are thoroughly dry you can spray a coat of Clear Acrylic Sealer over top to waterproof them.