Do not dip a knife in hot water. You shouldn't have to spread your flood icing enough to need to use a knife, and you certainly shouldn't be adding any extra moisture or heat to the icing. My recipes all come from this book, which I would totally suggest. http://www.amazon.ca/gp/aw/d/1580176941/ref=mp_s_a_1_1?qid=1396400529&sr=8-1 I use icing sugar, pasteurized egg whites, and warm water, with a bit of extract or lemon juice. The only difference between my piping icing and my flood icing is a tiny bit more warm water. I pipe, and let the borders dry for about an hour, then flood (getting into the edges with a toothpick) and allow to harden overnight before adding any details. Sorry I can't share the recipes - I lent the book out!