Fondant can stick to buttercream, but it is important to take a few steps to ensure a good bond.
First, make sure that the buttercream is completely dry and has formed a crust. This usually takes about 15-30 minutes, depending on the recipe and the environment. If the buttercream is too soft or sticky, the fondant may not adhere properly and could slide off or become misshapen.
Once the buttercream has formed a crust, lightly brush the surface with a small amount of water or piping gel. This will create a slightly tacky surface that will help the fondant adhere to the buttercream.
Next, roll out the fondant to the desired thickness and carefully drape it over the cake. Smooth the fondant gently with your hands, starting at the top and working your way down the sides. Use a fondant smoother to help remove any air bubbles and to create a smooth, even finish.
If the fondant starts to tear or crack, you can patch it by applying a small amount of water or piping gel to the tear and pressing it back together. Be careful not to use too much water, as this can cause the fondant to become sticky and lose its shape.
In general, fondant can adhere well to buttercream, but it is important to work carefully and patiently to create a smooth, seamless finish. With a little practice, you can achieve a beautiful and professional-looking cake.