I have had problems with the sides of layered cakes bulging through fondant where there is buttercream between layers. How do I keep thisa from happening
You need to let the cake settle for awhile with weight on it. I place wax paper on top of cake, then put a heavy book on top of it to push some pressure on cake, but not too much to crush it to break. I put that on there for minimum 1/2 hour or if can let it settle by itself, but would need to for hours. Good luck..
Yes, you need to let the cake settle, but you also need to not push down on your cake when you are smoothing fondant on it. Lots and lots of people do this to make the fondant "stick" or make it flat. All it does it make your filling bulge. Make sure you have a light touch!
Another point, make sure your bc is firm enough. I once had a problem with it being too runny and it bulged horribly which I then covered with a 'belt' made from fondant!
You should definately look into SugarShacks Perfecting the Art of Buttercream DVD (www.sugaredproductions.com)
Although it is a buttercream tips and tricks DVD, it addresses the bulge and I have not had bulge problems since using her techniques.