I'm making a wedding cake and as a "sample", I covered an 8" cake with fondant so the bride-to-be could decide if that is what she wanted. I used Satin Ice. I crumb-coated the cake and covered it. I didn't have a fondant smoother so I just did the best I could with my hands. It looked perfect. I forgot to buy a box and the cake store was closed so I used my old-fashioned cake-taker to keep the cake in overnight. The next day I took the cake to the bride-to-be which happens to be a co-worker, and lifted the lid. Lo and behold, there was a huge bubble on one side, and other smaller ones throughout. Also, the fondant showed some "droop" at the bottom. I used rolling pin rings (smaller ones) so I know the fondant couldn't have been too thick. What gives??? Humidity? Needless to say, she decided against the fondant which was fine by me!
Oh, I should mention, I painted on some luster on one side. Maybe the moisture seeped through?
did you let the cake mellow for a bit after baking to let the gasses escape? I usually bake one day and then it hang out for a day to let gasses escape. Then I fill, stack and crumb coat and let it hang out in the fridge again to settle for a couple hours... then when I fondant the cake I leave it on the counter in a cool dark spot. I never seal a fondant cake in plastic or cake taker or anything. I think maybe its important to let the fondant dry a touch in the air. I feel like it helps it hold its shape... maybe I am making stuff up here... but thats my logic. I am interested to see what others have to say.
Ahh...yes the dreaded bubble. I remeber when this happen to me. It could be a lot of things. Could be the temperature change. Could be icing to soon. Also did you give the cake a good push on top to lock in the filling to cake. Since my experience I make sure my cakes are completely cooled. I then make a thick dam of BC & spread the filling to the edges. Then when it's all filled & stacked I give a push on top to make sure there is no air bubbles trapped inside. Let the cake sit awhile then crumb coat of frost. Hope this helps.