I have an order for 5 DZ cupcakes and an 8" fondant covered cake with Nemo fondant figures for Saturday. I just found out the function will be at a park. I use all natural ingredients and therefore don't use shortening in my buttercream. I know butter melts at a certain temp. We are expecting 100 degrees here Saturday. I consulted with my customers and they would still prefer butter not shortening so how long do the cake/cupcakes have in this heat before it's a disaster? The plan right now is party starts at 1, I'll set everything up at 1:30 and cake activities start around 2. Advice greatly appreciated!!

Butter will hold in temps up to 95 degrees. The molecules are to delicate to stand higher temps. That is why most people will use shortening, it withstands heat well. If you keep them in the shade you would have a 50/50 chance. I would try to talk to the client and tell them, there is just no way unless they took a chance but it is up to them.

If they insist on the butter based frosting I'd have them sign a waiver. If temps hit 100 degrees, they might end up with soup on their cupcakes and you don't want them blaming you.
Good luck!

They definitely understand the melt factor. The event is in a pavilion with trees surrounding so they say it's shaded. I guess I just wanted to know if they will melt in 15-30 mins.

Put a stick of butter outside and see how long it lasts. I'm in Chicago where temps are in the high 90's all week. Even in my house with A/C my butter is softening in less than 30 minutes. There is no way I would do an all butter buttercream. Would they consider a mixture of vegetable shortening and butter? I would have them sign a waiver before agreeing to do this. Yes, I think they will be melted in 15-30 minutes, shade or no shade.