I'm making a dummy cake covered with fondant. I had no trouble covering the 9" round but I tried to cover the 12" round twice and each time the fondant along the top edge is cracking. Could it help to roll the fondant thinner? Do I need to bevel the top edge of the styrofoam (if so what should I use)? I just opened the fondant so it shouldn't be too dry. Maybe I'm not kneading the fondant long enough (how long should i knead the fondant before I roll?). Thanks for your help!

Press the top edge of the foam on a table to round it off. I roll my fondant to just under 1/4". After I do a fast smooth out of the top, the first thing I do is to quickly press the top inch of the side into place all the way around. This takes the pressure of the weight of the hanging fondant off that top edge. Then I can take my time smoothing the rest of the side into place. I also don't place the cake on a can as some suggest because that just lets the extra weight hang. I always place the cake on something that allows the excess fondant to rest on something so it doesn't pull down as much while I'm working it.

i havn't actually done a dummy cake before but i am going to very soon so here are the tips i heard:

You want to soften the top rim of the styrofoam with anything really just to give it a softer less sharp edge therefore less chance of cracking.

You don't want to roll the fondant too thin otherwise it might rip but too thick makes it hard to smooth the sides so i guess in between would be good (thats prob not very helpful lol)

Well sorry thats all i can think of to say lol