Hi there - getting ready to make my moms 70 birthday cake - we are going to use a presentation cake - 3 tiered- made with styrofoam cake rounds and then serve carrot cake cupcakes - the cake with be covered with fondunt and have fondunt shamrocks and other designs on it. I have never done one with the styrofoam and have a few questions -
Do I have to frost the styrofoam to have the fondunt stick?
How long can I start this in advance if it is not going to eaten (sp?)
In order to have the fondunt shamrocks stay on the cake I just brush the underside with water correct?
Do I have too worry about the green shamrocks bleeding onto the white fondunt on the cake?
Do I have to use a cardboard round on the bottom of each layer or can I just lay fondunt layer over fondunt layer?
Think thats it for now....thanks for your help - oh and sorry about the spelling.....
I lightly sand my styofoam to make sure it is very smooth (no bumps or rough edges) I also round the edges. You can lightly mist with water then apply the fondant.
Start whenever you want, dummies last forever! 
Yes, brush the backs of the shamrocks with a little bit of water, they will not bleed.
No cardboard rounds needed, just "glue" the tiers together with royal icing.
HTH!! 
Hi Leslie,
Question #1 - Yes, you have to ice the styrofoam, but what I have found that works very well rather than wasting icing is to brush the styrofoam with light corn syrup. Just make sure it is a light coating otherwise it may bleed out at the bottom. It really works well. 
Question #2 - You can start as early as your heart desires. The beauty of doing dummy cakes is that you can allow yourself as much time as you need.
Question #3 - Yes, just brush the back of your accent pieces with water and they will stick just fine. You can also make a fondant glue by taking a small piece of fondant and diluting it in hot water to make a fondant glue. Something along the lines of Elmer's glue is what you are looking for.
Question #4 - The color will only bleed if you put way too much water on the back of your fondant pieces. If you are going to use water, use a very, very, very light coat of water.
Question #5 - When I do dummy cakes, I never put cardboard rounds when stacking styrofoam to styrofoam. Only with the cake that is going on top of the styrofoam. The styrofoam to styrofoam gives you plenty of support and there is no need for doweling either. 
Good luck and let us know how it turns out!
Can't wait to see the pics!
Liz
thanks for your info - i had a very hard time finding the right size styrofoam so i ended up using hat boxes - so far so good - will post when done
Quote by @%username% on %date%
%body%