re: How To Get Smooth Butter Cream that Stands up to Heat and Humidity

If your cake has even a little condensation on the surface you will get air bubbles under your buttercream, so make sure that the cake is completely dry before you apply the buttercream. I usualy compress the icing alot during the smoothing process and this also helps to eliminate the dreaded air bubble bulge.
I lightly spray my cakes before I cover them with fondant.