I once made a sandcastle cake and I used graham cracker crumbs but instead of worrying about sticking the crumbs to fondant I just used buttercream which worked well enough. Maybe you could make buttercream that matches your fondant color (or even a sand color) and spread that where you need to attach sand?
I have also seen people use brown sugar for sand but in my opinion if there is going to be a lot on the cake rather then just a sprinkle for decoration the graham cracker crumbs are much tastier in large amounts.
© 2011-2017 CakesDecor.com. All Rights Reserved.
DISCLAIMER: Any posts on CakesDecor.com (CD) are posted by individuals acting in their own right and do not necessarily reflect the views of CD. CD will not be held liable for the actions of any user.