I used this gorgeous paper I found in the Tate Modern shop that is covered in all my favourite comic and sci-fi heroes. There was a "Heroes and Villians" and a "Heroines and Villainesses" so I made half and half - I now have boys and girls placemats!
It really was so easy. As you can see from my little collage, firstly get your old placements ready by giving them a quick sand - this gives a surface the paint can stick to. Then spray paint in your chosen colour - following whatever instructions are on your paint.
Once you are happy with the coverage, cut out whatever paper or papers you want to put on your placemats, then spray the back of the piece/s with spray mount. This wont affect any of the colours on the front, will give an even cover and most importantly allow you to reposition it if you get the placement wrong. Once happy leave to dry, then cover with 2 or 3 coats of spray varnish.
That's that, They work brilliantly, no peeling of the paper (its been a good 2 months of use now) and although I wouldn't recommend submersing them in water, they hold up to moisture perfectly fine. Quick, easy, and everyone thinks I paid megabucks for them!