Thank you guys!
Answering your questions:
@tullo: it would be better if I could cut away the bases but in this way it is stronger. Next time I will dilute what I use as groundwork a bit more so it can flow better around teh bases of the figures.
@Erik: I gave him only one match! One is enough to .......... OMG I think I hear a firetruck coming this way!
@Patrick: what I use for the groundwork is woodfiller and birdsand. The grass is from Games Workshop and is added by hand over some white glue, tipped of the excess grass and then I blow over it. Works well and I need no tools.