Jup as Calli says, make sure all surfaces are wet/damp before covering. I always keep a fan on full power on my cake. I ALSO before covering do fill the layers and let it settle with a weight ontop before finishing the sides. I only fridge for about 20 minutes before fondant. I only twice had a ring……or bulge…( luckily not serious) but this was when using a tiny amount of margarine in the ;buttercream, which was for home cakes. I only use lurpak lightly salted for b/c with a 2:1 sugar/butter ratio and 15 ml fluid including extract per 250g butter.
I am no pro but seems to work fine for me xx
Wallace x http://www.facebook.com/AWGHobbyCakes