Hi. If my buttercream is NOT crusting AT ALL what did I do wrong? That is the first question! Second is, I've decided to use MMF over this cake since it is not crusting to smooth with VIVA etc......... will there be a problem with the fondant adhering to the cake? When they go to cut it will the fondant just slide off?????
Post your exact recipe so we can see what might be causing it to not crust. It almost always a problems with the ratio of fat to PS. As far as using fondant, you'll be fine. I've never used a crusting buttercream myself and haven't had any problems from it.
I have used Wilton BC and put fondant on top w/o any problems. Crusting BC should work just as fine.
Yep, I've also used plain-old non-crusting buttercream under fondant and never had any problems (except when I made the layer of buttercream too thick and my fondant started to slide).