I can never get my buttercream completly smooth even with viva and a hot spatula. Seems like i miss the "right" time. My icing will be to soft n next time will have crusted, then i have a big mess. i check it often for the transition. Please Help.

Smoothing with a paper towel should work fine after the BC has crusted.  What exactly is happening when you try to smooth after crusting?  I usually give it 15 minutes or so after finishing smoothing with a pastry scraper, then check to see if it has crusted, then use the paper towel and a fondant smoother.  Can you describe the "big mess" you get after it has crusted?

the buttercream gets all rough looking from the crusting then the movement of the smoothing attempt. looks like u tried to smooth an already crusted cake n now it appers with little lumps from the previously dried crust

What buttercream recipe are you using?

Watch Jenniffer from cupadee, awesome tutorial,saved my life, I used to get so stressed smoothing buttercream.

http://cupadeecakes.blogspot.ca/2010/11/how-do-i-get-my-cakes-smooth.html