I have decorated 2 cakes with pink colored crusting buttercream lately. Both seem to have "cracked" on me before I even left the house with them.
1st cake applied buttercream the morning of...
2nd cake applied buttercream the evening before...
My recipe is 1/2 cup shortening, 4 cups powdered sugar, 4 tbls of water, and extract.
How can I prevent the cracking?

have you moved the cakes since you iced them? a lot of times i get cracks if i move cakes when the support underneath isn't strong enough and it causes them to bend a little. a spatula dunked in hot water and wiped off can help do the trick to smooth out cracks.

your sugar to fat ratio seems too high.

rule of thumb is one cup shortening to one pound ( 4 cups) of sugar for a nice crusting yet workable BC. also, try a liquid with fat rather than water, water seems to increase cracking, IMO

agree with above that you also need a form board under your cake or any icing will crack when moved.

HTH!

i had a friend that made the most beautiful cakes, and her frosting was wonderful, we lost touch i think she moved, but when i picked up a cake she alway's said support it in the middle, sometimes i'll get a cake that starts cracking it's so moist, i watched Edna's frost a cake and she uses alot of frosting, so i do that it hides my mistakes if i don't trim really even, and have used the hot spatula also.

I agree with Sugarshack... too much PS to fat ratio.... it's too dry...

The type of support is key. how many cardboards or what kind of plate was the cake on?

Thanks everyone for the help. I will try the recommendations that were mentioned!! The support also sounds like it could be an issue and will change that also.