I was hoping someone could give a Newbie some advice...I am making a 2 layer cake and want to put the diamond mat impression on the top layer. Do I do the impression before I place the cake on the bottom layer or when it's already on the bottom layer.

HELP!

I do the impression mat before.
I fondant the cake (you're using fondant right?)
Then lay the impression matt against it and push all over (usually with my fondant smoother while I hold the opposite side with another smoother .. or the top) then repeat on all sides.
Then I use my extremely scientific tool (the back of a butter knife) to make the indentations deeper.
Hope that helps...

I am actually using the crusted buttercream...does this matter? Should I then do after I place the cake on top of the bottom layer?

hmmmm.. maybe you should stack it first. Since you can't really pick up a buttercream cake like you can a fondant cake.

I really dont think it would hurt to do them either way. You can stack the fondant ones first too. But I'd definitly stack the buttercream before using the impression matt.

I have the same question. I tried practicing and my mat stuck to the buutercream. Guess I should have let it crust some more. Or could I give thwe mat a light dusting with corn starch or icing sugar to help it from sticking.

I will definitely stack first! And I will let it harden for a while before I try it!

If you stack it first, you are going to mess up the top of that bottom tier using the impression mat on the top one. You need to do it just like it is fondant - use the mat FIRST then stack. I have done it several times, no problem. (with buttercream) You may have to lightly dust the mat with cornstarch to keep it from sticking - and occasionally you have to go over the impression with another tool (knife or spatula) to make it look even all over.

Thank you so much everyone for the friendly and very helpful advice! It is greatly appreciated!