I made a 3D sculpted cake using Anne Reardon's template and instructions but the almost-finished cake started to melt and fall apart. We had extreme heat, and I had it in an air conditioned room (but didn't put it in the fridge after covering with fondant). Appreciate any tips on avoiding this next time?? In hindsight, I think that if I had covered the cake in ganache instead of buttercream, it might have held up. Or, I could have put the constructed cake in the fridge and then only covered it in fondant and finished decorating as late as possible close to the party. I was so happy I didn’t leave it right to the last minute (covered late Friday night so I could finish on Saturday for a Sunday morning party), but it had a whole day in heat and air conditioning for the buttercream to soften, and fondant to both soften and crack.

It had good support inside, so the structure was intact but the fondant & cake softened and melted from the outside in.

I learned a long time ago to keep my cakes in the refrigerator all the time.  If I don't, invariably, they sag and droop, even in the winter and our house is air conditioned.  When delivering, I always use a cool box, again, even in the winter.  So far, so good.  Also, when I do a 3D sculpted cake, I always cover it in ganache, even if I put buttercream over the ganache before covering it with fondant.  It does wonders for strengthening the structure.