Hi Norcalbaker59 and Becky
Thank you so much for your replies!
I am planning to make a square cake with royal icing covering it, with the New York skyline and buildings as decorations on the top and sides of the cake. I have made a 3D flat iron building (I have attached a photo of it IMG_8218, it's not great but i'm making a few different buildings so they will be hidden in between each other) and as I am not very good with piping icing I attached every dot for the windows using sugarpaste and water, which took me quite a while haha). I have put a little stick in that to pop on top of the cake. But knowing how long it took me to make the 3D building I’d imagine it will take me a while to make the several flat ones to go all the way along the side of the cake. I was worried if they were a week or so old if they would be too dry that water wouldn’t be strong enough to attach to the royal icing? I have seen some amazing ones online which I have attached a photo of, it is the look i am trying to do.
Thank you very much
Kind regards Lel
I’m glad you clarified as working with 2-D and 3-D are not the same.
Large 3-D sculpture cannot be glued to the side of a cake. It doesn’t matter what the cake is covered in. 3-D sculptures like these have to be attached with wires or dowels.
3-D large pieces need it to be as light as possible. Is your piece made from a solid piece of fondant?
If it is a solid piece of fondant, its not going to work well as the bulk and weight make it impossible to position and stay in place.
I would recommend you create a form of the building using rice crispy treats. Then wrap the form in fondant.
RIce crispy forms are pretty standard for large 3-D pieces as it reduces weight. Also, a solid piece of fondant takes forever to dry.
Rice crispy treats for sculpting is made a little bit differently than rice crispy treats for eating. The link below demonstrates how to make it. It also explains the basics in working with it.
https://sugargeekshow.com/recipe/rice-krispy-treats-recipe/
The form can be covered in fondant or modeling chocolate. It’s a personal preference. If you use fondant you need to apply to layers.
This video demonstrates how to cover in fondant.
I don’t use modeling chocolate so I can’t advise you on how to use it for sculpting.
Large heavy 3-D sculptures like this cannot be easily attached to the side of a cake. You have the added challenge of a hard royal icing.
With large 3-D pieces, you will need to build the rice crispy treat around a wire support. The wire is used to support the sculpture and give you something to insert into the cake for positioning.
The video link below explains how to create a wire form. While this is for a fondant cake topper the process is essentially the same. You would just simply use rice crispy treats.
NOTE: You should never stick plain wire into a cake. Use covered wire AND insert covered wire into a plastic straw. Trim wire so it does not stick out beyond the straw. Then insert in cake. I purchase small cocktail straws from the party supply store for this purpose.
In creating a sculpture around a wire form, orient the wire form in the direction you want to attach the sculpture to the cake. In other words, if the building is going to be attached to the cake from the back of the building, you would build the wire form and the rice crispy sculpture with the wire supports coming out of the back, rather than the side or bottom of he building.
Attaching such sculptures to royal icing is problematic. Royal icing dries hard. Royal icing is normally applied in two coats with a long drying period between coats. So inserting wire supports into the dried royal icing could cause cracking.
You could try inserting tiny cocktail straws into the cake where you want to attach the sculptures. Ice around the straws. Let the royal icing set up slightly then remove the straws. Before applying a second coating of royal icing insert fresh straws into the holes. Then remove them before the icing completely sets up. Then when you’re ready to attach the sculptures slide the straw covered wires in the preformed holes.
Water will never work to attach a sculpture of this size and weight to a cake. Your best bet would be to use edible glue. Edible glue is made with tylose powder. Also called CMC powder. It’s sold in most specialty cake stores as well as online.
Edible Glue
MAKE 24 hrs. BEFORE NEEDED!
1 cup boiling hot water
3/4 tsp tylose powder (CMC)
Boil water
Remove from heat
Stir in tylose powder until powder is thoroughly mixed in
Let cool and stir every 5 minutes until the tylose is completely dissolved, about 15-20 minutes.
Transfer to airtight bottle
Refrigerate overnight to allow the mixture to thicken and tylose to completely dissolve.
Write date on container. Tylose edible glue keeps up to 60 days refrigerated in an airtight container.
As 
