How can I successfully thicken my IMBC in order to pipe a stiff dam between layers? Thank you!!

Personally, I use a regular bc for the dam, as my imbc doesn't get stiff enough. JMO

I do it all the time. Just pipe a dam then if it's not stiff enough, put it in the freezer for 10 minutes and you'll have a really stiff dam. I am interested in knowing where you're located because my IMBC gets nice and stiff if I add really cold unsalted butter chips to the icing during the mixing process.

I agree with the previous poster. Just pipe it soft and pop it in the fridge. In 10 minutes it will be rock hard and you can fill it.

Annie

But when you go to serve the cake and it is sitting out and gets warm won't it settle and bulge?

Nope.

I have a theory about bulging and settling, and I think I'm right. I don't think I ever see anyone who uses a meringue bc complain of bulging. Why? Because that type of icing is very light weight. I don't have to let my cakes settle after filling. I still do for maybe a half hour, out of habit only at this point. American BCs have the weight of not only the shortening, but pounds and pounds of powdered sugar. The largest batch of MB I make, which fills a 6 qt bowl to the brim, has only 4.5 cups of sugar. 21 egg whites. I know the weight of that doesn't come close to the same amount of American BC. I fully believe bulging and sagging issues, are a result of using such heavy buttercreams.

And in my experience, when I fill and ice immediately afterwards, putting it in the fridge locks the cake in, if you will.