They were quick to make apart from letting the caulk dry, but some sponges just didn't adhere to well to the caulk or the other way around, so I spent ages easing them fully apart and got out my trusty hot glue gun and re stuck them. I don't think they will handle a lot of play before they fall apart. They were sent to my beautiful niece and nephew, who will enjoy them and have wonderful pretend play with them.
I did get some strange looks packing them into the postage box at the post office lol.
Update...28/05/2015.....the sponge cakes are still being played with and there has been some little separation but nothing major..although they are very expensive to buy at the "Pop Up Coffee and Cake Shop" run by my niece and nephew :)