I've heard that vikings were heavily tattooed is this true? If so how were they done?

I'm no expert but I think I can weigh in here, as I do have a passion and knowledge for Viking history.

According to the documentation by Ibn Fadlan of the Rus people, there were some who were tattooed. That being said, the Rus are arguably more of a Slavic people than a Scandinavian one, and to my knowledge nobody is really sure which is more prevalent in their culture. It is known that they travelled down the Volga River and had some origins in Eastern Sweden.

There's not a lot known on this topic in all honesty, but it's a good question, and one that I've had difficulty finding proper answers to myself. Hope that helps!

http://en.m.wikipedia.org/wiki/Ahmad_ibn_Fadlan