After I finished this cake, it kept its structure for hours. For probably at least 8 hours. Just before it was time to cut and eat it, the sides started falling off. What did I do wrong? It was 3 nine inch layers stacked. Should I have supported the layers? Did they shift?

This cake was just for a family gathering. It lasted long enough that the collapse didn't matter. But, I'm making it again next week for a friend. I would like it to be a disaster free cake!

.........It was 3 nine inch layers stacked. Should I have supported the layers? Did they shift?........

Without seeing any picture or having more information it is very hard to help you.
You say 3 layers -yes, it could have shifted. It would help to put some straws in to help keep it together. Did you put filling between the layers? Did you use a dam to hold the filling in? What kind was it? Is it hot/humid in your area? What kind of icing did you use?
Info, we need info

I think I figured out how to post a picture!



It was 3 layers that were from a 9" pan. I put icing between the layers, then iced the outside and put the planks against it.

Did the buttercream come off with the planks or did the planks separate from the buttercream? Nice cake!

Very cute cake, but if you didn't have a cake board under the top 2" layer and dowels in the bottom 4" tier, the weight of the fondant apples were just too much.

Rae

I didn't think about the weight of the apples. They are actually RKT, but they were still pretty weighty.

What if I put a board and dowels on the top layer and then did the apples on the board? It would be nice to have the 3 layers together. Do you think it would work?

Well, it would have helped, but the truth is, if those are 2" layers with buttercream and/or filling in between, as said above, the rule of thumb is to have a board and supports every 4" inches of cake.

Another option would have been to bake 4 layers, 1.5" each. This would yield 2, 3" tall tiers, each on it's own board with supports in the lower tier.

Personally, I would have done the 1.5" layers, 2 "tier" cake, and then put supports in the TOP tier, too, put a fondant covered board on it & added the apples. This would have supported the weight of the apples and also made serving easy.

I did something very similar with this steamer pot cake:


The cake was 8" tall--2, 4" split & filled tiers, 5 supports in bottom tier, 3 in top tier holding up a fondant covered board decorated with clams, lobster, & corn cobs. Client removed "topper" before serving.

Rae

The lobster cake is amazinig! I like the idea of the 1.5" tiers also. I will definitely do it that way. Thanks for the advice!