No, but I find it helps. Another thing that helps is just letting the cake sit overnight, well-covered of course so it doesn't dry out. This can be either at room temperature, in the fridge or in the freezer. Apparently there is some air that needs to escape the cake before you put fondant on it, or else air pockets tend to form under your fondant layer. But whatever you decide to do, I think you'll find using fondant is a lot of fun.
I have never used a weight on my cakes - but I also press on each layer after I fill to make sure that everything is level and all air leaks out. I also let my cakes set in the fridge for at least a half hour between each step (i.e. fill all layers - sit. Crumb coat - sit. Completely frost cake - sit. Then fondant).
Also - I read this somewhere but can't remember where, if you spray your cake with a little water before putting your fondant on, it really does help keep the fondant stuck on the cake and prevent air bubbles.
Good luck - I'm sure you will have lots of fun!
I actually wrap my cakes in plastic wrap while they are still hot. Then stack them on top of each other (wrap them seperatly) Then like an hour later I put swap them so they push the air out of themselves.
They take about 4 hours to fully cool. But I never ever get airbubbles. and the steam in the plastic wrap seems to keep them extra moist
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