Originally Posted by indydebi
It's hard to say with a situation of "I used the same recipe except I changed this and this and this......"
I love when people review recipes and give it a negative review with a statement like that.
I'm always careful about changing too many things in a recipe at one time, because things do react differently.
What is the original recipe you used? Is this a recipe you have used with success? What was the 'new' recipe that you actually used?
I have suggested people add corn starch to thicken up icing, but I'm not sure that it helps with humidity issues. I do use a tablespoon of meringue powder per lb of sugar to help with stability.
From my experience, heavy cream is thicker than water, so when I have used (whipping) cream I have found that I needed to add more than I would if I was using water. Is it possible that the water/coffee creamer mixture was thinner and you didn't need as much?
In my experience icing that looks like it is separating is usually too thin. But then again icing that doesn't want to stick to the cake is usually too thick, so it's hard to really know with out being able to see it.
My thought would be, if you have the stuff, go ahead and make a fresh batch of icing, especially if this is a cake for someone else.
Once that cake is done you can play around with this one to see if you can fix it. Maybe taking a small amount of it and adding some powders sugar to it?