So, I made a full sheet cake the other day. First time doing a sheet cake that big (I usually try to stay away from sheet cake). It was a donated cake so I wasn't too worried but I have a new contract for full sheet cake once a month starting in Nov. for a corporate client, so I need some answers....
I bought a full size board and box at the local cake supply store. Bake my two 12 x 18 ('cause the size is supposed to be 18 x 24, right?), put the cakes on the board and lo and behold there is barely enough room for icing on the sides let alone any borders!!!!! 
What's up with that? I trimmed the cake down a bit on the two long sides to give me some room 
!!!
Did I bake the wrong size? What should I know for next time?
Oh, yeah...and I doubled the board and I still had some little cracks (that I could see- no one else could) in my crusting buttercream. How do I prevent that????
Help me!!!!
TIA!
Yes, that's the amount of edging left when using standard boards. (My cake supply shop has a GREAT supply of everything, so I can get even bigger boards from her.)
If I'm not getting the board back, I will use 3 or 4 cardboards. I may use 3 Plus deliver it on a board I cut from Lowe's. Upon arrival, I slide the cake-n-cardboard off of the delivery board onto their table.
I have had sheet cake boards cut out of plywood. I made mine 21 x 27 . The icing doesn't crack ...of course I covered it several times with contact paper then I cover it with the decorative paper of choice 
Hope this helps you on your cracking question.... It doesn't have to be real thick...mine I think is a little over a inch thick
I do however ask for the boards back and they have no problems with that.
HTH
Have a great day!!
christi
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