I've tried a denser cake, and thicker icing, but lately, once my cake is covered with fondant, the icing seems to bulge out between the tiers! How do I make it smooth?

And Merry Christmas & Happy Holidays to all!

Try putting yourcrumb coated cake in the freezer for 10 to 15 mins before you cover it. So it is nic:e and firm then leave it in the fridge over night. Hope this helps you

Are you using a dense icing dam around the edge of the filling layer? Do a search for 'filling dam', or 'buttercream dam' on this website. There are many informative threads on this very topic, and will instruct you on the importance of using a dam (or ganache), building your cake tier, weighting it for several hours until it settles, then applying a crumb coat, then fondant etc.

HTH!

I will try both of those tips! I've never had this problem before but lately it seems like it's happening all the time :s it looks ghastly!

Thanks so much for the advice!

The weight of the sugarpaste is squeezing the filling out from between the layers.

Perhaps use
1. a thicker filling
2. a thinner layer of filling
3. dam the edges with a thick bead of icing
4. a thinner cover of sugarpaste to lessen it's weight

A denser cake adds to the weight that is compressing the filling ..
A cold/chilled/frozen crumbcoat under sugarpaste may lead to condensation that will dissolve the sugarpaste. Or the sugarpaste may slip on the condensed surface .. It will not affect the weight issue. Once it warms up again, it will soften ..

layers and tiers are two separate things...i'm glad everyone else figured this out! another reason could be temperature in your area or where you're baking...if you pull a cake from a cold fridge into the heat then you might get bulging. also, after filling your cake you need to let it settle for at least an hour...you can rest a small plate or something on top of it to help speed the process; but in the case of settling you want your cake and fillings to sore of meld together and compress the air out.

also, don't fill your cakes when they are warm

One point no one has pointed out yet is that your layers *must* be level. If no nothing you do will solve this problem.